Re: [time-nuts] Sidereal Time and Lady Heather.
On Thu, 20 Dec 2012 14:39:21 +1100, Neville Michie wrote: I have just found out how to get sidereal time from Lady Heather. (You put t=GMST in the command line, or alias target line, and the Lady comes up in Sidereal Time, ticking away in Sidereal seconds.) (Also you can get LMST, LAST or GAST.) Now, as a time nut, I have questions. How is a leap second handled? Leap seconds are handled by the GPS receiver, not by Lady Heather. Some receivers add a 60th second for the leap second, others insert an extra 00th second. Sidereal time is time observed by watching stars rather than the sun. In fact it is the source of all knowledge about how fast our planet rotates, and the basis for all our time scales. A sidereal second is shorter than a physical second by about one second in six minutes, so as to fit 366.25 sidereal days into the year of 365.25 solar days. At the Vernal Equinox there is a situation where Solar seconds exactly match the Sidereal second count, as zero, but how can a time nut know if this is in error? How accurate is it? In microseconds, nanoseconds? My interest in Sidereal time is because I have two pendulum clocks mounted on the same brick wall and they interfere with each other. By running one one sidereal time they are independent. The problem is to get a source of sidereal time to measure the performance of the sidereal clock. It is no problem to divide 10 MHz down to sidereal seconds, but how do you synch. the seconds? This is where the Lady helps. But I do not know how I can get really accurate seconds markers as convenient as the PPS from my Thunderbolt. Even though Lady Heather can display LMST, LAST or GAST it runs at solar rate, not siderial rate. Each second still rolls over at the top of the solar second. Thus there is a one second sawtooth error in siderial time with a 365+ second repitation period. I have two Thunderbolts running copies of Lady Heather and two other GPS receivers running Tac32. Tac32 also runs at solar rate, but can display siderial time to nearest 0.01 sec. So I was able to compare Lady Heather with Tac32. cheers, Neville Michie Bill Beam NL7F ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
On Fri, Jun 15, 2012 at 9:49 PM, Mark Sims hol...@hotmail.com wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). I think the question was how to get Sidereal time to the microsecond level. A computer display screen only gets refreshed roughly 60 to 100 times per second so a screen can be tens of milliseconds off. How is this done professionally. Basically they don't. What you do is record a UTC time code on a track parallel to the data. Or now that everything is digital, the time code is sampled and multiplexed with the data. Later the display software can convert the time to whatever format is desired. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi, First of all why would you want Sidereal Time to that level of precision? I know this is the time-nuts so 'because I can' is a perfectly acceptable answer. These days Sidereal Time is only used to display to humans in a recognizable format an old and outdated approximation to the current ITRF - ICRF transformations that the professionals would use to find or track a celestial object. See IERS (http://www.iers.org/IERS/EN/DataProducts/data.html) and SOFA (http://www.iausofa.org/index.html) for the details and sample code in FORTRAN and 'C' for these transformations. I suspect if you want microsecond accuracy you will have to use the SOFA routines, and have access to the IERS EOP Data. Cheers Ken On 16/06/12 07:20, Chris Albertson wrote: On Fri, Jun 15, 2012 at 9:49 PM, Mark Simshol...@hotmail.com wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). I think the question was how to get Sidereal time to the microsecond level. A computer display screen only gets refreshed roughly 60 to 100 times per second so a screen can be tens of milliseconds off. How is this done professionally. Basically they don't. What you do is record a UTC time code on a track parallel to the data. Or now that everything is digital, the time code is sampled and multiplexed with the data. Later the display software can convert the time to whatever format is desired. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
It started with trying to run two long case regulators on one brick wall. Although the wall is founded on bedrock they interfere with each other. As I want to study their performance I tuned one to sidereal time, now they are independent. I run a TBOLT and a LPRO to maintain a mean time clock for the clock analysis. I am hoping to get a chip from TVB to divide the TBOLT or rubidium 10MHz down to PPS at sidereal rate to observe the performance of the sidereal regulator. Now I want to be able to set the sidereal time standard so, if I lose power on my rubidium, I can reset it so the longterm record of the sidereal long case will have no phase jumps. Also it seemed like a good idea, and the more it seems difficult, the more it needs to be done. cheers, Neville Michie On 16/06/2012, at 5:51 PM, Ken Duffill wrote: Hi, First of all why would you want Sidereal Time to that level of precision? I know this is the time-nuts so 'because I can' is a perfectly acceptable answer. These days Sidereal Time is only used to display to humans in a recognizable format an old and outdated approximation to the current ITRF - ICRF transformations that the professionals would use to find or track a celestial object. See IERS (http://www.iers.org/IERS/EN/DataProducts/data.html) and SOFA (http://www.iausofa.org/index.html) for the details and sample code in FORTRAN and 'C' for these transformations. I suspect if you want microsecond accuracy you will have to use the SOFA routines, and have access to the IERS EOP Data. Cheers Ken On 16/06/12 07:20, Chris Albertson wrote: On Fri, Jun 15, 2012 at 9:49 PM, Mark Simshol...@hotmail.com wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). I think the question was how to get Sidereal time to the microsecond level. A computer display screen only gets refreshed roughly 60 to 100 times per second so a screen can be tens of milliseconds off. How is this done professionally. Basically they don't. What you do is record a UTC time code on a track parallel to the data. Or now that everything is digital, the time code is sampled and multiplexed with the data. Later the display software can convert the time to whatever format is desired. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Ok so you really are NOT needing the EOP Data that deals with the irregularities of the Earth Rotation. In fact it sounds to me like you are not really looking for Sidereal time at all. Sidereal Time is not a uniform time scale and so sounds like it is inappropriate for your needs. If you get a source of Sidereal Time, from somewhere that claims to be able to give it to you to microsecond accuracy, there is a high probability that they will be taking things like nutation into account. Certainly if you use the SOFA routines I alluded to earlier they will. Again it sounds to me like what you are really looking for is an independent source of uniform time based on the PPS produced by the divider in the chip TVB will get for you, which is then very close to the MEAN sidereal second. The way Astronomers used to do it, they would have clocks regulated to the mean Sidereal Second, but have to recalibrate them every day (actually every night!). And they were not interested to the microsecond. It was the search for that level of accuracy that forced them to move away from this non-uniform timescale and produced the ICRF/ICRS and ITRF/ITRS that they now use. HTH Ken On 16/06/12 10:57, Neville Michie wrote: It started with trying to run two long case regulators on one brick wall. Although the wall is founded on bedrock they interfere with each other. As I want to study their performance I tuned one to sidereal time, now they are independent. I run a TBOLT and a LPRO to maintain a mean time clock for the clock analysis. I am hoping to get a chip from TVB to divide the TBOLT or rubidium 10MHz down to PPS at sidereal rate to observe the performance of the sidereal regulator. Now I want to be able to set the sidereal time standard so, if I lose power on my rubidium, I can reset it so the longterm record of the sidereal long case will have no phase jumps. Also it seemed like a good idea, and the more it seems difficult, the more it needs to be done. cheers, Neville Michie On 16/06/2012, at 5:51 PM, Ken Duffill wrote: Hi, First of all why would you want Sidereal Time to that level of precision? I know this is the time-nuts so 'because I can' is a perfectly acceptable answer. These days Sidereal Time is only used to display to humans in a recognizable format an old and outdated approximation to the current ITRF- ICRF transformations that the professionals would use to find or track a celestial object. See IERS (http://www.iers.org/IERS/EN/DataProducts/data.html) and SOFA (http://www.iausofa.org/index.html) for the details and sample code in FORTRAN and 'C' for these transformations. I suspect if you want microsecond accuracy you will have to use the SOFA routines, and have access to the IERS EOP Data. Cheers Ken On 16/06/12 07:20, Chris Albertson wrote: On Fri, Jun 15, 2012 at 9:49 PM, Mark Simshol...@hotmail.com wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). I think the question was how to get Sidereal time to the microsecond level. A computer display screen only gets refreshed roughly 60 to 100 times per second so a screen can be tens of milliseconds off. How is this done professionally. Basically they don't. What you do is record a UTC time code on a track parallel to the data. Or now that everything is digital, the time code is sampled and multiplexed with the data. Later the display software can convert the time to whatever format is desired. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
On 6/15/12 9:49 PM, Mark Sims wrote: Lady Heather can do sidereal time. Specify either the LMST, LAST, GMST or GAST time zone (for Local/Greenwich Mean/Apparent Sidereal Time). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. you can do what I do to drive mars time clocks. Hydrogen maser derived 10 MHz into a HP 3325B set for the right rate for the clock (i.e. slightly less than 32kHz). I wouldn't be true sidereal time (because the rate is uniform), but it's an easy and straightforward approach. (and no, the Maser derived 10 MHz isn't needed, but I happen to have it handy, so why not) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
namic...@gmail.com said: I have been trying to set up a clock on sidereal time. My only source of a time calculator is tycho.usno.navy.mil, but this seems to be off the air for the last week or more. Is there any other source of sidereal time? The basic method needs a current almanac and I can not even find a source of one of those. How you would find ST to a microsecond is not obvious. How do radio astronomers do it? cheers, I expect the answer is to receive UTC or GPS time and convert that to Sidereal. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
And to think, I just used a CD4046 phase locked loop to multiply a precise 60 Hz by 1465 and then divide the resultant 87,900 Hz by 1461 to get 60 Hz times 1.00273785 or 60.164271 Hz to drive a digital clock. The error between using 1.00273785 and 1.00273790934, as determined by Reid and Honeycut, was only -0.005 seconds per day or -1.85 seconds per year. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Friday, January 15, 2010 9:47 PM To: j...@quik.com; Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Sidereal time J. Forster wrote: That's the point I was making earlier. Most telescopes have a FOV of at least 15 arc-minutes. You only need to get the guide stars into the field and go from there. Also, a telescope's pointing can be off in BOTH RA and Dec. Dec has nothing to do with siderial time. While displaying Hour Minutes and Seconds of apparent local sidereal time may be fun, the actual need is to calculate an angle in degrees and minutes for which the object of interest position can be converted into suitable pointing angle. The simplest approximation can make use of the fact that on 365,25 normal days, there is 366,25 sidreal days. The error of that approximation is 366,25/366,2425/365,25*365,2425 - 1 = -5,6E-8 days/day or -1,211 arcmin per day or -0,44 arcmin per year. The Gregorian correction was used for comparision value rather than a tabulated value, but I was lazy to get a quick back-off-envelope type of result. My point being that fairly simple approximate gears could be used to give a good-enought result such that remaining drift can be compensated using regular observation. Pointing towards known fix-stars for calibration of local position, local pointing error and clock offset would end up as a single correction factor of pointing angle correction. The only thing one wants is that date, time and position sets the local sidreal time close enought for manual correction to be a matter of minor adjustments. To convert the day (D) of a year into a sidreal day (DS) one gets DS = D*366,25/365,25 = D + D/365,25 For hours we would use the relation HS = 24*DS, D = DI + H/24 and used modulo 24 HS = 24*D + 24*D/365,25 = 24*DI + H + 24*D/365,25 = H + 24*D/365,25 Thus, the time of day is adjusted with the date, but there is no need to calculate the full number of seconds. Similarly may the time of day be converted to degrees. AS = 360*DS mod 360 = 360*D + D*360/365,25 mod 360 = 360*DI + 15*H + DI*360/365,25 + H*15/365,25 mod 360 = 15*H + H*15/365,25 + DI*360/365,25 mod 360 H is then broken into HI, MI and SI for normal wall-clock representation. This approximate convertion on the back-of-envelope level has silently ignored the phase error, but retracing to the USNO webpage should allow a more thorough calculation of a suitable offset. The remaining mod 360 operation needs to handle the addition of three 0-360 degree ranges, so the range only needs to extend over 1080 degrees. From the above formula it becomes apparent that the pointing needs an adjustment of about a degree every day and about 2,464 arcmin every hour. So, a very coarse calculation could be good enought. A fairly trivial calculation with a correction from date and fine-correction for hour and minute may provide enought pointing precission. It is trivial to correct for local offset from the UTC time using the GPS position. Should be doable even for a tiny processor. Should be not too hard to include into a motor control to keep the scope pointed to the right point. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Sounds good to me, but since this is time-nuts, you need a GPIB connection to the synthesizer so you can tweak it to track the details from IERS. It would be interesting to work out the details and see which is the most-significant digit that changes. Would you need to tweak the synthesizer, or are the changes off the bottom? Plan B: Do it in software. Consider a small CPU running from 10 MHz that can drive a display. If it has a connection to the outside world, then you can tell it how many ticks per sidereal second and when to start using the new value. Small LCDs are not expensive. There are some designed to fit into a disk/CD slot on PCs. SparkFun has Arduinos for $30 and LCDs for $14 and up. Some assembly required. Or get their Serial Enabled LCD for $30 which includes a PIC16F88 and figure out how to reprogram it to keep time. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Really?? you'd better tell USNO, NRAO etc. Bruce mike cook wrote: No such thing as a siderial second. Le 15/01/2010 05:04, Neville Michie a écrit : It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve 2010/1/15 Brian Kirby kilodelta4foxm...@gmail.com: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD A man with one clock knows what time it is; A man with two clocks is never quite sure. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Before the advent of automated telescopes that can point to an object of interest a wall clock displaying local sidereal time was commonly used to help point a telescope using setting circles and the known coordinates of the (astronomical) object of interest. Bruce Steve Rooke wrote: Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve 2010/1/15 Brian Kirbykilodelta4foxm...@gmail.com: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
We still use it at the observatory. For example, my object of interest is up between 0h and 17h LMST and a quick glance at the sideral clock let's me know where I am. Jim 2010/1/15 Bruce Griffiths bruce.griffi...@xtra.co.nz Before the advent of automated telescopes that can point to an object of interest a wall clock displaying local sidereal time was commonly used to help point a telescope using setting circles and the known coordinates of the (astronomical) object of interest. Bruce Steve Rooke wrote: Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve 2010/1/15 Brian Kirbykilodelta4foxm...@gmail.com: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi Gee, there's an idea. Grab a TBolt and a simple micro. Hook them up to something like a Soekris and a big LED display. Network it up to get the latest offsets. Toss in a bit of wire and software and you get very high accuracy sidereal time. If NTP is good enough you could dispense with the TBolt and part of the wire. Tough to see the difference between NTP and GPS on a wall clock Bob On Jan 15, 2010, at 4:27 AM, Hal Murray wrote: If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Sounds good to me, but since this is time-nuts, you need a GPIB connection to the synthesizer so you can tweak it to track the details from IERS. It would be interesting to work out the details and see which is the most-significant digit that changes. Would you need to tweak the synthesizer, or are the changes off the bottom? Plan B: Do it in software. Consider a small CPU running from 10 MHz that can drive a display. If it has a connection to the outside world, then you can tell it how many ticks per sidereal second and when to start using the new value. Small LCDs are not expensive. There are some designed to fit into a disk/CD slot on PCs. SparkFun has Arduinos for $30 and LCDs for $14 and up. Some assembly required. Or get their Serial Enabled LCD for $30 which includes a PIC16F88 and figure out how to reprogram it to keep time. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi There may be a gotcha. If that HP box has their standard time base in it, your idea isn't going to work. The normal HP approach is to lock a local oscillator up to the incoming reference input. That way they can handle a bunch of different time base inputs without much bother. Their standard VCXO does not have enough range to lock to a reference 0.03% off frequency. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Brian Kirby Sent: Thursday, January 14, 2010 10:13 PM To: precise time Subject: [time-nuts] Sidereal time I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
This is all quite interesting. 6 years ago, for the MER rovers, I cobbled together a scheme to drive off-the-shelf 24hr electric clocks off a 3325A to run on Mars time (which is slightly slower than Earth time). Same scheme can be used for sidereal time, or to make an indicator that runs at varying speeds (e.g. If you wanted to make a sophisticated tide clock or moon clock or something). A microprocessor which adds/drops pulses in the 32.768 kHz reference input is probably the cleanest way. On 1/15/10 1:27 AM, Hal Murray hmur...@megapathdsl.net wrote: If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Sounds good to me, but since this is time-nuts, you need a GPIB connection to the synthesizer so you can tweak it to track the details from IERS. It would be interesting to work out the details and see which is the most-significant digit that changes. Would you need to tweak the synthesizer, or are the changes off the bottom? Plan B: Do it in software. Consider a small CPU running from 10 MHz that can drive a display. If it has a connection to the outside world, then you can tell it how many ticks per sidereal second and when to start using the new value. Small LCDs are not expensive. There are some designed to fit into a disk/CD slot on PCs. SparkFun has Arduinos for $30 and LCDs for $14 and up. Some assembly required. Or get their Serial Enabled LCD for $30 which includes a PIC16F88 and figure out how to reprogram it to keep time. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Sure it is.. In observatories, for instance, they'll have a sidereal time display, because that's what's important. You know that Sirius crosses a N/S line at a particular sidereal time (or more correctly, isn't that the right ascension.. When the body crosses the meridian) On 1/15/10 2:07 AM, Steve Rooke sar10...@gmail.com wrote: Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
True. At the observatory where I worked in the 70s there was a very accurate pendulum clock with a contact that incremented the clocks in the domes every siderial second. -John = Before the advent of automated telescopes that can point to an object of interest a wall clock displaying local sidereal time was commonly used to help point a telescope using setting circles and the known coordinates of the (astronomical) object of interest. Bruce Steve Rooke wrote: Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve 2010/1/15 Brian Kirbykilodelta4foxm...@gmail.com: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Heresy: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. -John === Hi Gee, there's an idea. Grab a TBolt and a simple micro. Hook them up to something like a Soekris and a big LED display. Network it up to get the latest offsets. Toss in a bit of wire and software and you get very high accuracy sidereal time. If NTP is good enough you could dispense with the TBolt and part of the wire. Tough to see the difference between NTP and GPS on a wall clock Bob On Jan 15, 2010, at 4:27 AM, Hal Murray wrote: If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Sounds good to me, but since this is time-nuts, you need a GPIB connection to the synthesizer so you can tweak it to track the details from IERS. It would be interesting to work out the details and see which is the most-significant digit that changes. Would you need to tweak the synthesizer, or are the changes off the bottom? Plan B: Do it in software. Consider a small CPU running from 10 MHz that can drive a display. If it has a connection to the outside world, then you can tell it how many ticks per sidereal second and when to start using the new value. Small LCDs are not expensive. There are some designed to fit into a disk/CD slot on PCs. SparkFun has Arduinos for $30 and LCDs for $14 and up. Some assembly required. Or get their Serial Enabled LCD for $30 which includes a PIC16F88 and figure out how to reprogram it to keep time. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
On 1/15/10 9:13 AM, J. Forster j...@quik.com wrote: Heresy: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. -John = Celestial Navigation? Essentially, one determines longitude by figuring out what the difference between local solar time and sidereal time is. Now, what is super accurate? 40,000 km =24hrs, so 1 second is about 460 meters. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
The external input triggers logic (via a selectable divider). It would easily go +/- 50% in frequency. Artek Media has the manual. -John = Hi There may be a gotcha. If that HP box has their standard time base in it, your idea isn't going to work. The normal HP approach is to lock a local oscillator up to the incoming reference input. That way they can handle a bunch of different time base inputs without much bother. Their standard VCXO does not have enough range to lock to a reference 0.03% off frequency. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Brian Kirby Sent: Thursday, January 14, 2010 10:13 PM To: precise time Subject: [time-nuts] Sidereal time I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi Ok, so NTP is indeed good enough for the application. Each millisecond bumps you a half meter... Grab a beater PC or Soekris board and write some code. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Lux, Jim (337C) Sent: Friday, January 15, 2010 12:22 PM To: j...@quik.com; Discussion of precise time and frequencymeasurement Subject: Re: [time-nuts] Sidereal time On 1/15/10 9:13 AM, J. Forster j...@quik.com wrote: Heresy: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. -John = Celestial Navigation? Essentially, one determines longitude by figuring out what the difference between local solar time and sidereal time is. Now, what is super accurate? 40,000 km =24hrs, so 1 second is about 460 meters. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hmm. This gives me an idea of what to do with my second Western Union Self-Winding clock. I currently use a Soekris Net4501, modified in a manner similar to John Ackerman's, driven by a Thunderbolt. I use one of the GPIO pins to provide the hourly synchronization pulse to my clock. If I adjust the pundulum appropriately and modify my little program, the second clock can show sidereal time. Ralph True. At the observatory where I worked in the 70s there was a very accurate pendulum clock with a contact that incremented the clocks in the domes every siderial second. -John = Before the advent of automated telescopes that can point to an object of interest a wall clock displaying local sidereal time was commonly used to help point a telescope using setting circles and the known coordinates of the (astronomical) object of interest. Bruce Steve Rooke wrote: Hi Brian, I really love this group, it appeals to the technophile inside me and it's interesting to see the answers that are given. You should have know that posting to a nuts group would mean you would get lots of highly technical responses but frequently the questions posed are not answered as things go off in a tangent. Perhaps we should have asked you how accurately bang on the sidereal second?? you wish this clock to be or perhaps you just wish it to tick over the sidereal time without some frame of reference? Sounds like an interesting idea, sorry but I cannot answer your questions conclusively but it looks sound to me. What you are doing is fitting a sidereal day into a wall clock day display by driving the clock with fast seconds so it's 24 hours is over in 23 hours 56 minutes and 4.091 seconds. If that's what you want to do, it sounds great even though I'm not sure that a sidereal day is normally presented that way. 73, Steve 2010/1/15 Brian Kirbykilodelta4foxm...@gmail.com: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi So now the question becomes: With only modest / reversible butchery, what's the slowest pulse train it will accept? 1 MHz is not to bad to generate. Something slower would still be easier with a computer. If 1 ms accuracy is good enough then driving it with anything over 10 KHz is kind of overkill. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: Friday, January 15, 2010 12:28 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Sidereal time The external input triggers logic (via a selectable divider). It would easily go +/- 50% in frequency. Artek Media has the manual. -John = Hi There may be a gotcha. If that HP box has their standard time base in it, your idea isn't going to work. The normal HP approach is to lock a local oscillator up to the incoming reference input. That way they can handle a bunch of different time base inputs without much bother. Their standard VCXO does not have enough range to lock to a reference 0.03% off frequency. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Brian Kirby Sent: Thursday, January 14, 2010 10:13 PM To: precise time Subject: [time-nuts] Sidereal time I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Looing at the schematics quickly, it looks like 1 MHz. There is a clock failure circuit on that line. -John = Hi So now the question becomes: With only modest / reversible butchery, what's the slowest pulse train it will accept? 1 MHz is not to bad to generate. Something slower would still be easier with a computer. If 1 ms accuracy is good enough then driving it with anything over 10 KHz is kind of overkill. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: Friday, January 15, 2010 12:28 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Sidereal time The external input triggers logic (via a selectable divider). It would easily go +/- 50% in frequency. Artek Media has the manual. -John = Hi There may be a gotcha. If that HP box has their standard time base in it, your idea isn't going to work. The normal HP approach is to lock a local oscillator up to the incoming reference input. That way they can handle a bunch of different time base inputs without much bother. Their standard VCXO does not have enough range to lock to a reference 0.03% off frequency. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Brian Kirby Sent: Thursday, January 14, 2010 10:13 PM To: precise time Subject: [time-nuts] Sidereal time I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Brian, Last I looked, the solar/sidereal ratio was in fact 1:1.00273790935 though that was a while back. I build precision pendulum clocks and in designing a clock that would beat seconds and tell mean time as well as sidereal time I used a gear train of 15/47x49/97x82/31/x87/37 as I remember, which gave me an error of approximately .0073 secs/year sidereal. I know it's a bit arcane for this group, but the accuracy isn't bad! Doing the equation of time is mechanically a bigger pia... Bill S Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
If you actually need the apparent local sidereal time then the corrections detailed at: http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/approx-sider-time may be necessary. Bruce Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
I'm not sure your friend needs the time at all. Telescope tracking mounts have a periodic error due to non-perfect mechanical parts. The usual way to remove this error is to train the mount by manually guiding it through one or more periods, or - probably more common these days - use an optical autoguider. Jim On 1:59 PM, Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
j...@quik.com said: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. What's the field of view of a telescope? (or the guide scope?) What's the ballpark distortion of the atmosphere? -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
One needs to know the local apparent sidereal time to aid initial acquisition of the target. Periodic error correction and using an autoguider are of little or no use for this operation. However correction for encoder error axis non orthogonality, encoder eccentricity and bending of the telescope tube an the mount may be required. A pointing model for the telescope is derived from the pointing (not tracking errors) errors for a set of target objects uniformly distributed over the sky. For further details see: http://www.tpsoft.demon.co.uk/ Bruce Jim King wrote: I'm not sure your friend needs the time at all. Telescope tracking mounts have a periodic error due to non-perfect mechanical parts. The usual way to remove this error is to train the mount by manually guiding it through one or more periods, or - probably more common these days - use an optical autoguider. Jim On 1:59 PM, Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
That's the point I was making earlier. Most telescopes have a FOV of at least 15 arc-minutes. You only need to get the guide stars into the field and go from there. Also, a telescope's pointing can be off in BOTH RA and Dec. Dec has nothing to do with siderial time. -John == [snip] - probably more common these days - use an optical autoguider. Jim On 1:59 PM, Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
The two big ones I remember are: A Boller Chivens 24 about 1 degree A 60 about 15 arc-minutes The MMT is about 1 degree, I think. -John = j...@quik.com said: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. What's the field of view of a telescope? (or the guide scope?) What's the ballpark distortion of the atmosphere? -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
J. Forster wrote: That's the point I was making earlier. Most telescopes have a FOV of at least 15 arc-minutes. You only need to get the guide stars into the field and go from there. Also, a telescope's pointing can be off in BOTH RA and Dec. Dec has nothing to do with siderial time. If the axes arent exactly orthogonal or the polar axis (assuming an equatorial mount) then the declination as measured by the telescope encoder is dependent on time. -John If the mount is alt-alt altazimuth etc then both axis coorrdinates are time dependent. An automated telescope doesn't always have an observer available to do the fine pointing corrections. Since there has been no statement about the telescope aperture or field of view the assumption that the FOV is 15 arc minutes or more may be invalid. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
These are all OPEN LOOP corrections. They are better than nothing, but nowhere near as good as properly implemented auto-guiding which is closed loop. They are certainly not as good as even the simplest Adaptive Optics utilizing only a Tip-Tilt tracker. -John == One needs to know the local apparent sidereal time to aid initial acquisition of the target. Periodic error correction and using an autoguider are of little or no use for this operation. However correction for encoder error axis non orthogonality, encoder eccentricity and bending of the telescope tube an the mount may be required. A pointing model for the telescope is derived from the pointing (not tracking errors) errors for a set of target objects uniformly distributed over the sky. For further details see: http://www.tpsoft.demon.co.uk/ Bruce Jim King wrote: I'm not sure your friend needs the time at all. Telescope tracking mounts have a periodic error due to non-perfect mechanical parts. The usual way to remove this error is to train the mount by manually guiding it through one or more periods, or - probably more common these days - use an optical autoguider. Jim On 1:59 PM, Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
J. Forster wrote: The two big ones I remember are: A Boller Chivens 24 about 1 degree Only with a camera, not with an eyepiece. Eyepiece field of view is something like 20 arc minutes with a 2 eyepiece. A 60 about 15 arc-minutes The MMT is about 1 degree, I think. No one uses an eyepiece with the MMT (something of a misnomer now that it uses a single primary mirror). The quoted FOV is for a camera only -John = Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
J. Forster wrote: The two big ones I remember are: A Boller Chivens 24 about 1 degree Only with a camera, not with an eyepiece. True, but telescopes have guide scopes with much shorter focal lengths, typically 1 vs 9 meters. Eyepiece field of view is something like 20 arc minutes with a 2 eyepiece. A 60 about 15 arc-minutes The MMT is about 1 degree, I think. No one uses an eyepiece with the MMT (something of a misnomer now that it uses a single primary mirror). The quoted FOV is for a camera only -John = Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
J. Forster wrote: That's the point I was making earlier. Most telescopes have a FOV of at least 15 arc-minutes. You only need to get the guide stars into the field and go from there. Also, a telescope's pointing can be off in BOTH RA and Dec. Dec has nothing to do with siderial time. If the axes arent exactly orthogonal or the polar axis (assuming an equatorial mount) then the declination as measured by the telescope encoder is dependent on time. That effect is second order at most. Do the trig. -John If the mount is alt-alt altazimuth etc then both axis coorrdinates are time dependent. An automated telescope doesn't always have an observer available to do the fine pointing corrections. Serious telescopes have auto-trackers. You put the cursor on the guide star and put it into track mode. Since there has been no statement about the telescope aperture or field of view the assumption that the FOV is 15 arc minutes or more may be invalid. See other email for examples. -John === Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
You have missed the point entirely. Autoguiders etc are only useful for tracking an object once it has been acquired. Pointing is the ability to point the telescope at a desired object or location starting from home or another position in the sky. With large telescopes (or with inexperienced operators) one doesnt have the time for manual correction. It is desirable to place the object of interest close to the centre of the field. Once it is acquired then use of autoguiders and periodic error correction (an open loop process) can be used to track the object. When cloud cover permits, a wide angle (8 to 15 degree FOV) camera fixed to the telescope can be used to implement a high accuracy (1 arc sec or so) encoder. Bruce J. Forster wrote: These are all OPEN LOOP corrections. They are better than nothing, but nowhere near as good as properly implemented auto-guiding which is closed loop. They are certainly not as good as even the simplest Adaptive Optics utilizing only a Tip-Tilt tracker. -John == One needs to know the local apparent sidereal time to aid initial acquisition of the target. Periodic error correction and using an autoguider are of little or no use for this operation. However correction for encoder error axis non orthogonality, encoder eccentricity and bending of the telescope tube an the mount may be required. A pointing model for the telescope is derived from the pointing (not tracking errors) errors for a set of target objects uniformly distributed over the sky. For further details see: http://www.tpsoft.demon.co.uk/ Bruce Jim King wrote: I'm not sure your friend needs the time at all. Telescope tracking mounts have a periodic error due to non-perfect mechanical parts. The usual way to remove this error is to train the mount by manually guiding it through one or more periods, or - probably more common these days - use an optical autoguider. Jim On 1:59 PM, Brooke Clarke wrote: Hi Brian: Why? Do you just want to see the sidereal time on a display or do you need a digital output? The Spark Fun serial enabled displays use what's called a back pack that has the PIC 16F88 uC and it's used to do serial data to LCD parallel data can control lines. I've made some clocks using that chip. http://www.prc68.com/I/PIC16F88.shtml http://www.prc68.com/I/PRC68COM.shtml#07092006 A friend is setting up an observatory where the pointing accuracy of the telescope mount is specified as 7 arcseconds or less peak-to-peak periodic error before correction. Much better after correction. That implies he needs to know what time it is within tens of milliseconds. http://www.prc68.com/I/StellarTime.shtml#StrMov We looked into different ways to get the time into his computer to that accuracy and NTP looks like it will fill the bill, so a GPS receiver may not be required. Have Fun, Brooke Clarke http://www.PRC68.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
---BeginMessage--- Finder charts are of no use with either an inexperienced observer or an automated telescope. Bruce J. Forster wrote: My girl friend is a regular observer (w/ a PhD) at the Smithsonian Astrophysical Observatory and uses the instruments at Mt. Hopkins all the time. I KNOW what she does. Their finder charts got to better than 20th magnitude, NOT just bright objects. -John J. Forster wrote: J. Forster wrote: The two big ones I remember are: A BollerChivens 24 about 1 degree Only with a camera, not with an eyepiece. True, but telescopes have guide scopes with much shorter focal lengths, typically 1 vs 9 meters. It isnt always possible to find an operator who has the time or expertise to use a guide scope together with a finder chart properly. This restricts them to bright objects like the moon Jupiter, Saturn etc. Locating Uranus, Neptune etc is out of the question. If the object of interest is too faint to see in the guide scope then accurate pointing is essential. The technique of offsetting from a visible object in the guide scope or finder scope isn't easy to learn. An automated telescope needs to have accurate pointing to acquire the object of interest. When one is using an instrument (e.g. spectrograph, photometer) with a narrow field of view the pointing accuracy becomes critical to reduce the search time required to acquire the object of interest. Eyepiece field of view is something like 20 arc minutes with a 2 eyepiece. A 60 about 15 arc-minutes The MMT is about 1 degree, I think. No one uses an eyepiece with the MMT (something of a misnomer now that it uses a single primary mirror). The quoted FOV is for a camera only -John = Bruce Bruce ---End Message--- ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
---BeginMessage--- Of course not, but that isn't relevant either to the original thread or the general problem of pointing. But while we are discussing the MMT it has an altazimuth mount, Both axis coordinates are dependent on the local apparent sidereal time when tracking celestial objects. Bruce J. Forster wrote: Inexperienced operators don't get to play with $100,000,000 toys. -John == Finder charts are of no use with either an inexperienced observer or an automated telescope. Bruce J. Forster wrote: My girl friend is a regular observer (w/ a PhD) at the Smithsonian Astrophysical Observatory and uses the instruments at Mt. Hopkins all the time. I KNOW what she does. Their finder charts got to better than 20th magnitude, NOT just bright objects. -John J. Forster wrote: J. Forster wrote: The two big ones I remember are: A Boller Chivens 24 about 1 degree Only with a camera, not with an eyepiece. True, but telescopes have guide scopes with much shorter focal lengths, typically 1 vs 9 meters. It isnt always possible to find an operator who has the time or expertise to use a guide scope together with a finder chart properly. This restricts them to bright objects like the moon Jupiter, Saturn etc. Locating Uranus, Neptune etc is out of the question. If the object of interest is too faint to see in the guide scope then accurate pointing is essential. The technique of offsetting from a visible object in the guide scope or finder scope isn't easy to learn. An automated telescope needs to have accurate pointing to acquire the object of interest. When one is using an instrument (e.g. spectrograph, photometer) with a narrow field of view the pointing accuracy becomes critical to reduce the search time required to acquire the object of interest. Eyepiece field of view is something like 20 arc minutes with a 2 eyepiece. A 60 about 15 arc-minutes The MMT is about 1 degree, I think. No one uses an eyepiece with the MMT (something of a misnomer now that it uses a single primary mirror). The quoted FOV is for a camera only -John = Bruce Bruce ---End Message--- ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Performance of an early pointing model for the MMT is given in: http://www.mmto.org/MMTpapers/pdfs/tm/tm03-3.pdf Pointing error performance was around 1.6 arc sec rms Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
On 1/15/10 9:13 AM, J. Forster j...@quik.com wrote: Heresy: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. -John What if it's a *radio* telescope? Or a DSN dish? Both of those have to track sidereal motion. At Ka-band, the 70meter dish needs pointing on the order of 1 millidegree. That's about 250 milliseconds, I guess. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Lux, Jim (337C) wrote: On 1/15/10 9:13 AM, J. Forster j...@quik.com wrote: Heresy: Why do you really NEED super accurate siderial time? If you are using it to point a telescope, you only need it accurate enough to get the guide stars into the field. Remember, the atmosphere refracts kinda randomly. -John What if it's a *radio* telescope? Or a DSN dish? Both of those have to track sidereal motion. At Ka-band, the 70meter dish needs pointing on the order of 1 millidegree. That's about 250 milliseconds, I guess. Or better yet, a submillimeter radiotelescope? At the SMT on Mt. Graham, we measure pointing to 0.1 arcsecond and have typical pointing errors of ~2 arcseconds. These are measured at many points in the sky using 5-point data (center, N, E, W, S offsets) from a planet. The pointing model gets updated regularly as needed. The tracking system receives IRIG time from a GPSDO directly. The time accuracy needed is ~1 millisecond. LST is calculated using the canonical 10 digit number cited previously. --David Forbes, the HHSMT, Arizona ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Magnus Danielson wrote: J. Forster wrote: That's the point I was making earlier. Most telescopes have a FOV of at least 15 arc-minutes. You only need to get the guide stars into the field and go from there. Also, a telescope's pointing can be off in BOTH RA and Dec. Dec has nothing to do with siderial time. While displaying Hour Minutes and Seconds of apparent local sidereal time may be fun, the actual need is to calculate an angle in degrees and minutes for which the object of interest position can be converted into suitable pointing angle. The simplest approximation can make use of the fact that on 365,25 normal days, there is 366,25 sidreal days. The error of that approximation is 366,25/366,2425/365,25*365,2425 - 1 = -5,6E-8 days/day or -1,211 arcmin per day or -0,44 arcmin per year. The Gregorian correction was used for comparision value rather than a tabulated value, but I was lazy to get a quick back-off-envelope type of result. My point being that fairly simple approximate gears could be used to give a good-enought result such that remaining drift can be compensated using regular observation. Pointing towards known fix-stars for calibration of local position, local pointing error and clock offset would end up as a single correction factor of pointing angle correction. The only thing one wants is that date, time and position sets the local sidreal time close enought for manual correction to be a matter of minor adjustments. To convert the day (D) of a year into a sidreal day (DS) one gets DS = D*366,25/365,25 = D + D/365,25 For hours we would use the relation HS = 24*DS, D = DI + H/24 and used modulo 24 HS = 24*D + 24*D/365,25 = 24*DI + H + 24*D/365,25 = H + 24*D/365,25 Thus, the time of day is adjusted with the date, but there is no need to calculate the full number of seconds. Similarly may the time of day be converted to degrees. AS = 360*DS mod 360 = 360*D + D*360/365,25 mod 360 = 360*DI + 15*H + DI*360/365,25 + H*15/365,25 mod 360 = 15*H + H*15/365,25 + DI*360/365,25 mod 360 H is then broken into HI, MI and SI for normal wall-clock representation. This approximate convertion on the back-of-envelope level has silently ignored the phase error, but retracing to the USNO webpage should allow a more thorough calculation of a suitable offset. The remaining mod 360 operation needs to handle the addition of three 0-360 degree ranges, so the range only needs to extend over 1080 degrees. From the above formula it becomes apparent that the pointing needs an adjustment of about a degree every day and about 2,464 arcmin every hour. So, a very coarse calculation could be good enought. A fairly trivial calculation with a correction from date and fine-correction for hour and minute may provide enought pointing precission. It is trivial to correct for local offset from the UTC time using the GPS position. Should be doable even for a tiny processor. Should be not too hard to include into a motor control to keep the scope pointed to the right point. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. Hej Magnus No one bothers with such gear ratios for a modern telescope as its cheaper to use a computer than have a set of custom gears made. In any case, direct drive of the axes is sometimes used - no gears: http://www.halfmann-teleskoptechnik.com/e_index.htm Calculating the time is just the beginning if you want to point to Saturn for which the RA and DEC vary over time and the simple model isn't very accurate: http://ssd.jpl.nasa.gov/horizons.cgi Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Magnus, I learned a technique for adjusting time that doesn't require floating point calculations, back when a FP Package significantly slowed micro processing, circa 1980. Use a preset counter to count incoming pulses, perhaps 1 PPS. Set it for the number of pulses that will make a one pulse adjustment, up or down. When it rolls over, double or cancel the next pulse on its way to the clock counter. The maximum clock display error is one pulse. To carry it out to several decimal places, you need successively larger counters to add or subtract a pulse. I know this is heresy, but you don't need any programming skills, or micros and compiler packages and endian calculations and debug tools and training time to do this simple pulse manipulation in hardware. If a person has programming skills, it is possible to implement the counters and adjustments in a micro that doesn't have FP math. Ah, I don't think or -1,211 arcmin per day or -0,44 arcmin per year is correct. More change per day than per year? What have I missed? FWIW, Bill Hawkins -Original Message- From: Magnus Danielson Sent: Friday, January 15, 2010 8:48 PM While displaying Hour Minutes and Seconds of apparent local sidereal time may be fun, the actual need is to calculate an angle in degrees and minutes for which the object of interest position can be converted into suitable pointing angle. The simplest approximation can make use of the fact that on 365,25 normal days, there is 366,25 sidreal days. The error of that approximation is 366,25/366,2425/365,25*365,2425 - 1 = -5,6E-8 days/day or -1,211 arcmin per day or -0,44 arcmin per year. The Gregorian correction was used for comparision value rather than a tabulated value, but I was lazy to get a quick back-off-envelope type of result. My point being that fairly simple approximate gears could be used to give a good-enought result such that remaining drift can be compensated using regular observation. Pointing towards known fix-stars for calibration of local position, local pointing error and clock offset would end up as a single correction factor of pointing angle correction. The only thing one wants is that date, time and position sets the local sidreal time close enought for manual correction to be a matter of minor adjustments. To convert the day (D) of a year into a sidreal day (DS) one gets DS = D*366,25/365,25 = D + D/365,25 For hours we would use the relation HS = 24*DS, D = DI + H/24 and used modulo 24 HS = 24*D + 24*D/365,25 = 24*DI + H + 24*D/365,25 = H + 24*D/365,25 Thus, the time of day is adjusted with the date, but there is no need to calculate the full number of seconds. Similarly may the time of day be converted to degrees. AS = 360*DS mod 360 = 360*D + D*360/365,25 mod 360 = 360*DI + 15*H + DI*360/365,25 + H*15/365,25 mod 360 = 15*H + H*15/365,25 + DI*360/365,25 mod 360 H is then broken into HI, MI and SI for normal wall-clock representation. This approximate convertion on the back-of-envelope level has silently ignored the phase error, but retracing to the USNO webpage should allow a more thorough calculation of a suitable offset. The remaining mod 360 operation needs to handle the addition of three 0-360 degree ranges, so the range only needs to extend over 1080 degrees. From the above formula it becomes apparent that the pointing needs an adjustment of about a degree every day and about 2,464 arcmin every hour. So, a very coarse calculation could be good enought. A fairly trivial calculation with a correction from date and fine-correction for hour and minute may provide enought pointing precission. It is trivial to correct for local offset from the UTC time using the GPS position. Should be doable even for a tiny processor. Should be not too hard to include into a motor control to keep the scope pointed to the right point. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hej Bruce, Bruce Griffiths wrote: Hej Magnus No one bothers with such gear ratios for a modern telescope as its cheaper to use a computer than have a set of custom gears made. In any case, direct drive of the axes is sometimes used - no gears: http://www.halfmann-teleskoptechnik.com/e_index.htm Calculating the time is just the beginning if you want to point to Saturn for which the RA and DEC vary over time and the simple model isn't very accurate: http://ssd.jpl.nasa.gov/horizons.cgi I was meaning mathematical gears, not mechanical gears. The simplified approach was just to present an alternative for those in need of a little less precission as their scopes and associated pointing needs is a little less than the large scopes. Just as an idea. The main idea was that the open-loop calculations could be simplified if a calibration would create a closed-loop for the offset part and remaining open-loop errors would be relative negligable for the application. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Bill Hawkins wrote: Magnus, I learned a technique for adjusting time that doesn't require floating point calculations, back when a FP Package significantly slowed micro processing, circa 1980. I still remember those times, even if I did not do any computing then. Use a preset counter to count incoming pulses, perhaps 1 PPS. Set it for the number of pulses that will make a one pulse adjustment, up or down. When it rolls over, double or cancel the next pulse on its way to the clock counter. The maximum clock display error is one pulse. To carry it out to several decimal places, you need successively larger counters to add or subtract a pulse. I know this is heresy, but you don't need any programming skills, or micros and compiler packages and endian calculations and debug tools and training time to do this simple pulse manipulation in hardware. True, while programming isn't prohibiting me from doing fun, back-of-the-envelope design sketches can reduce complexity regardless of implementation form. If you have the fullblown 64-bit (or better) IEEE-754 float to fool around with, then this is less of a problem. If a person has programming skills, it is possible to implement the counters and adjustments in a micro that doesn't have FP math. Certainly, that was my aim. Ah, I don't think or -1,211 arcmin per day or -0,44 arcmin per year is correct. More change per day than per year? What have I missed? I missed a e-3 exponent on the first number... so it is -0,07266 arcsec per dayor -26,6 arcsec a year. Thus, that's the approximate error of the method of mapping 365,25 days onto 366,25 sidreal days rather than using more accurate numbers. I still used approximate numbers (Gregorian correction) to get the rough value rather than a tabulated value from an athorative source rather than the back of my head. The main point was to show that even an very coarse approximate approach may be good enought for simpler cases, and the simplified and reduced math may allow for relativly simple calculations. The ,25 part just begs for a x4 to transform into integer numbers. So its 365,25 = 1461/4 and 366,25 = 1465/4. AS = 15*H + H*60/1461 + DI*360*4/1461 mod 360 H = HI + MI/60 + SI/3600 Using the above H formula with integer second indications (SI) will form a limit of resolution, but then again, I would not point a larger scope using this approximation anyway. AS = 15*HI + MI/4 + SI/900 + HI*60/1461 + MI/1461 + SI/60/1461 + DI*360*4/1461 mod 360 Scale appropriatly, add position and correction values as needed before breaking down into output form. It might be helpfull to reduce further by realizing that 1461 = 3*487 and 3 is used for several of the multiplicative constants, so /487 can be used for all but MI. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Wait 'till EXACTLY the Spring Equinox? -John == Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Hi Depending on exactly how the 59309 works, you might do better by chopping into it and feeding it with a micro that added an extra pulse every so often. That would allow you to stick some math in-between a UTC pps source and your clock. Let the micro go get all the magic numbers from USNO and keep everything right. Bob On Jan 14, 2010, at 10:12 PM, Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
The 59309A is a GPIB interfaced clock unit and can be set to a specific time via the GPIB interface. It also puts out the time and date via the GPIB. So it can be set to a specific siderial time from an external UTC clock w/ the appropriate SW to compute Siderial Time from UTC. -John === It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
Sidereal Time is another form of Earth Orientation angle based time where the orientation angle reference is the fixed stars instead of the mean sun. You need to take such effects as precession, nutation and polar motion into account. The rate isn't uniform with respect to atomic time. The (rate) ratio of UT1 to mean sidereal time is defined to be 0.997269566329084 − 5.8684×10−11T + 5.9×10−15T², where T is the number of Julian centuries of 36525 days each that have elapsed since JD 2451545.0 (J2000). If you are using UTC broadcasts to determine Sidereal time, you first need to correct UTC to obtain UT1 by applying the correction DUT1 ( UTC -UT1). DUT1 predictions etc are available from IERS. Bruce Neville Michie wrote: It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
If you are going to do that computation, HP has a Digital Display (59304A) for the GPIB in the very same family of instruments. -John == Sidereal Time is another form of Earth Orientation angle based time where the orientation angle reference is the fixed stars instead of the mean sun. You need to take such effects as precession, nutation and polar motion into account. The rate isn't uniform with respect to atomic time. The (rate) ratio of UT1 to mean sidereal time is defined to be 0.997269566329084 â 5.8684Ã10â11T + 5.9Ã10â15T², where T is the number of Julian centuries of 36525 days each that have elapsed since JD 2451545.0 (J2000). If you are using UTC broadcasts to determine Sidereal time, you first need to correct UTC to obtain UT1 by applying the correction DUT1 ( UTC -UT1). DUT1 predictions etc are available from IERS. Bruce Neville Michie wrote: It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sidereal time
No such thing as a siderial second. Le 15/01/2010 05:04, Neville Michie a écrit : It is an interesting question, we are so used to WWV and GPS with regular time signals to synchronise clocks to mean solar time. One method is to get a pocket calculator to identify a time in the future when a siderial second nearly corresponds to a UTC second and use the PPS pulse from GPS to jam a preset time into the Siderial clock, (or start a halted clock with the correct time preset. How long you have to wait for corresponding seconds depends on how accurate you want it. cheers, Neville Michie On 15/01/2010, at 2:25 PM, Bruce Griffiths wrote: Brian Kirby wrote: I would like to have an electronic clock to keep sidereal time. I am planning on using a HP 59309A, which can except an external clock of 1/5/10 Mhz. According to Wikipedia sidereal time is 23 hours 56 minutes and 4.091 seconds - a total of 86,164.091 seconds So 86,400 seconds for a normal atomic defined day divided by 86,164.091 = 1.002,737,903,89 If I set the 59309A to 10 Mhz external clock and dial a synthesizer up to 10.0273790, the unit should be able to keep sidereal time. Is my math and theory correct ? Brian - KD4FM That just gives the rate. How are you going to set the actual Sidereal time to better than the 0.9s that can be deduced from UTC? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
