Re: [time-nuts] establishing your position w/o gps
Finding your location without GPS is not all that difficult. You need a quality theodolite, but even an ordinary one will read to 1 second of arc. You observe circumpolar stars at night to obtain a true azimuth. (North and South) and also the latitude by the inclination of the pole. On a time photograph these stars draw circles around the pole, the centre of the circle is the celestial pole and its elevation above the horizon gives the latitude. You can also use an almanac and a calendar to determine your latitude by observing stars with the theodolite. You observe the sun at noon to find the local time and set your local clock. You then wait for an event like an eclipse of a planets moons to establish the relationship between your local time and the time at a known site. A theodolite has a telescope that can be plunged i.e. used upside down and this technique is used to get a very accurate level from a striding level. No pool of mercury is needed. The setting up of a theodolite uses sitings and reversed sitings to set the vertical level. The main error is the atmospheric refraction which scatters individual observations, so many repeated observations are needed. The local time observations need to be repeated for good accuracy. A sextant is a less accurate instrument that has the main redeeming feature that when reading it you superimpose the image of a star or the sun with the image of the horizon. Although the image seen may be rolling around, the position of the sun on the horizon is rock steady and is adjusted by the thimble for coincidence. The elevation is then read off the vernier. A theodolite needs a solid base to work from and would be useless on a ship. cheers, Neville Michie On 25/01/2012, at 12:52 PM, Jim Lux wrote: On 1/24/12 3:19 PM, J. Forster wrote: Is the USNO almana/ephemeris still published in hard copy every year? That had moon timing, etc. You can download pieces from the Astronomical Applications website at USNO. Or you can buy a copy of the Nautical Almanac for about $20 from a variety of sources. You could also download the pdf (but printing it would cost you more than the $20).. Amazon has it, for instance. http://www.usno.navy.mil/USNO/astronomical-applications/ publications/naut-almanac will find it, but the GPO version is more expensive than the commercial versions.. ___ 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] establishing your position w/o gps
Finding your location without GPS is not all that difficult. You need a quality theodolite, but even an ordinary one will read to 1 second of arc. Ordinary? You mean something like a Wild T-2 or Kern DKM-2. Even then getting close to 1 arc-second requires a lot of care. You observe circumpolar stars at night to obtain a true azimuth. (North and South) and also the latitude by the inclination of the pole. Not quite so straight forward. You have to have accurate siderial time and an almanac. Polaris is only near the pole, not at it. On a time photograph these stars draw circles around the pole, the centre of the circle is the celestial pole and its elevation above the horizon gives the latitude. You can also use an almanac and a calendar to determine your latitude by observing stars with the theodolite. Not so easy. At the celestial equator the stars are moving in Hour Angle at 15 arc-seconds per second. -John == You observe the sun at noon to find the local time and set your local clock. You then wait for an event like an eclipse of a planets moons to establish the relationship between your local time and the time at a known site. A theodolite has a telescope that can be plunged i.e. used upside down and this technique is used to get a very accurate level from a striding level. No pool of mercury is needed. The setting up of a theodolite uses sitings and reversed sitings to set the vertical level. The main error is the atmospheric refraction which scatters individual observations, so many repeated observations are needed. The local time observations need to be repeated for good accuracy. A sextant is a less accurate instrument that has the main redeeming feature that when reading it you superimpose the image of a star or the sun with the image of the horizon. Although the image seen may be rolling around, the position of the sun on the horizon is rock steady and is adjusted by the thimble for coincidence. The elevation is then read off the vernier. A theodolite needs a solid base to work from and would be useless on a ship. cheers, Neville Michie On 25/01/2012, at 12:52 PM, Jim Lux wrote: On 1/24/12 3:19 PM, J. Forster wrote: Is the USNO almana/ephemeris still published in hard copy every year? That had moon timing, etc. You can download pieces from the Astronomical Applications website at USNO. Or you can buy a copy of the Nautical Almanac for about $20 from a variety of sources. You could also download the pdf (but printing it would cost you more than the $20).. Amazon has it, for instance. http://www.usno.navy.mil/USNO/astronomical-applications/ publications/naut-almanac will find it, but the GPO version is more expensive than the commercial versions.. ___ 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] establishing your position w/o gps
On 26/01/2012, at 2:49 AM, J. Forster wrote: Finding your location without GPS is not all that difficult. You need a quality theodolite, but even an ordinary one will read to 1 second of arc. Ordinary? You mean something like a Wild T-2 or Kern DKM-2. Even then getting close to 1 arc-second requires a lot of care. A wild T1 reads directly to 6 seconds, but with repetition will get 1 second. Unlike digital instruments you need a little bit of skill and persistence to get the best measurement from an analogue instrument. You observe circumpolar stars at night to obtain a true azimuth. (North and South) and also the latitude by the inclination of the pole. Not quite so straight forward. You have to have accurate siderial time and an almanac. Polaris is only near the pole, not at it. No need for time, you follow the azimuth of the star until it turns around and then again until it turns back. Half the difference gives you the azimuth of the pole very accurately. Fit your observations to a parabola to get a good result. Works best in Winter when the sun is down for more than 12 hours. A good technique as refraction errors cancel. On a time photograph these stars draw circles around the pole, the centre of the circle is the celestial pole and its elevation above the horizon gives the latitude. You can also use an almanac and a calendar to determine your latitude by observing stars with the theodolite. Not so easy. At the celestial equator the stars are moving in Hour Angle at 15 arc-seconds per second. As I said, analogue measurements need some skill and perseverance. If you added more modern technology you could track your theodolite/ telescope with a clock so you would get a longer period to adjust/ observe the observations and set your clock. Neville -John == You observe the sun at noon to find the local time and set your local clock. You then wait for an event like an eclipse of a planets moons to establish the relationship between your local time and the time at a known site. A theodolite has a telescope that can be plunged i.e. used upside down and this technique is used to get a very accurate level from a striding level. No pool of mercury is needed. The setting up of a theodolite uses sitings and reversed sitings to set the vertical level. The main error is the atmospheric refraction which scatters individual observations, so many repeated observations are needed. The local time observations need to be repeated for good accuracy. A sextant is a less accurate instrument that has the main redeeming feature that when reading it you superimpose the image of a star or the sun with the image of the horizon. Although the image seen may be rolling around, the position of the sun on the horizon is rock steady and is adjusted by the thimble for coincidence. The elevation is then read off the vernier. A theodolite needs a solid base to work from and would be useless on a ship. cheers, Neville Michie On 25/01/2012, at 12:52 PM, Jim Lux wrote: On 1/24/12 3:19 PM, J. Forster wrote: Is the USNO almana/ephemeris still published in hard copy every year? That had moon timing, etc. You can download pieces from the Astronomical Applications website at USNO. Or you can buy a copy of the Nautical Almanac for about $20 from a variety of sources. You could also download the pdf (but printing it would cost you more than the $20).. Amazon has it, for instance. http://www.usno.navy.mil/USNO/astronomical-applications/ publications/naut-almanac will find it, but the GPO version is more expensive than the commercial versions.. ___ 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] establishing your position w/o gps
Ordinary? You mean something like a Wild T-2 or Kern DKM-2. Even then getting close to 1 arc-second requires a lot of care. A wild T1 reads directly to 6 seconds, but with repetition will get 1 second. Unlike digital instruments you need a little bit of skill and persistence to get the best measurement from an analogue instrument. Assuming youcan do that w/o bias. A T-2 ius a 1 ard second instrument, a T-3 is 0.1 arc-second. I've never seen a T-4 in the flesh. You observe circumpolar stars at night to obtain a true azimuth. (North and South) and also the latitude by the inclination of the pole. That means observations over more than 18 hours. It'll take you most of a year, unless you are above the artic circle. Not quite so straight forward. You have to have accurate siderial time and an almanac. Polaris is only near the pole, not at it. No need for time, you follow the azimuth of the star until it turns around and then again until it turns back. Half the difference gives you the azimuth of the pole very accurately. See above. Fit your observations to a parabola to get a good result. Works best in Winter when the sun is down for more than 12 hours. A good technique as refraction errors cancel. In practice, the seeing is nowhere near 1 arc-second for 2-3 aperture 'scopes. On a time photograph these stars draw circles around the pole, the centre of the circle is the celestial pole and its elevation above the horizon gives the latitude. And to do that you need a sub-arc second telescope mount. You just can't mount a camera on a tripod. You can also use an almanac and a calendar to determine your latitude by observing stars with the theodolite. Not so easy. At the celestial equator the stars are moving in Hour Angle at 15 arc-seconds per second. As I said, analogue measurements need some skill and perseverance. That's an understatement. I've done it, both for North lines and to adjust a 24 telescope. If you added more modern technology you could track your theodolite/ telescope with a clock so you would get a longer period to adjust/ observe the observations and set your clock. Neville The modern technology just makes the angle readout direct. -John == ___ 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] establishing your position w/o gps
Moin, All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? I know that most countries established a coordinate system in the last 100-200 years. But astronomy has been around much longer and had the need for precise timing and postioning. So, how did the gentlemen back in the good old days tell what time it was, where they were and where they were looking? How was the first global geodetic system established? Wikipedia has a few interesting articles, but not much about how it is actually done. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] establishing your position w/o gps
In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Back then the stars were the coordinate system and the position of the telescope the unknown, so you did it by observing stars with documented coordinates with your new telescope and then you set your clock and calculated your lattitude accordingly. Remember: back then longitude and time were as single convolved coordinate. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] establishing your position w/o gps
On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Back then the stars were the coordinate system and the position of the telescope the unknown, so you did it by observing stars with documented coordinates with your new telescope and then you set your clock and calculated your lattitude accordingly. Remember: back then longitude and time were as single convolved coordinate. That's what i'm aiming at. Yes, the lattitude can be calculated using angle measurements relative to a known horizontal plane (mercury mirror) or a vertical line (plumb bob). Still not easy to get below an arc minute, but doable. But how do you untangle longitude and time? How do you know that you are looking exactly south (or north)? Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] establishing your position w/o gps
In message 20120124121642.4a8ad1def54bc32cca928...@kinali.ch, Attila Kinali w rites: On Tue, 24 Jan 2012 11:04:08 + But how do you untangle longitude and time? How do you know that you are looking exactly south (or north)? North/South can be done by timing (widely spaced in inclination) stellar transits relative to each other. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] establishing your position w/o gps
On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know.The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away.But in the 1500's they could only know the location after the fact when they returned -- 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] establishing your position w/o gps
Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know.The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away.But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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] establishing your position w/o gps
Maybe the Longitude Act was issued also because of the disaster occured in 1707 due to a navigation error: the Royal Navy fleet lost 4 of its 15 ships. On Tue, Jan 24, 2012 at 5:50 PM, Azelio Boriani azelio.bori...@screen.itwrote: Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.com wrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know.The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away.But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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] establishing your position w/o gps
If you're looking for a really interesting topic to read about, the development of an accurate ship-board clock is really fascinating! And it wasn't done overnight! Lee K9WRU - Original Message - From: Chris Albertson albertson.ch...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, January 24, 2012 10:36 AM Subject: Re: [time-nuts] establishing your position w/o gps On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. ___ 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] establishing your position w/o gps
I've read the book by Dava Sobel Longitude... not technical but interesting for me. On Tue, Jan 24, 2012 at 6:05 PM, Lee Mushel herbe...@centurytel.net wrote: If you're looking for a really interesting topic to read about, the development of an accurate ship-board clock is really fascinating! And it wasn't done overnight! Lee K9WRU - Original Message - From: Chris Albertson albertson.ch...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, January 24, 2012 10:36 AM Subject: Re: [time-nuts] establishing your position w/o gps On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.**312d60bd4fccce4f3e71c136@**kinali.ch20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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] establishing your position w/o gps
I think James Burke discussed these clocks in one of his documentary series. Besides not using a pendulum, they were temperature compensated by using materials with opposite temperature coefficients of expansion and then gimbaled for use on a rolling and pitching ship. Oddly enough, the phase locked loop came significantly earlier when a clock maker used it to regulate pendulum clocks overnight to quickly calibrate a new clock to a reference clock. On Tue, 24 Jan 2012 17:50:54 +0100, Azelio Boriani azelio.bori...@screen.it wrote: Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know.The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away.But in the 1500's they could only know the location after the fact when they returned ___ 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] establishing your position w/o gps
On Tue, 24 Jan 2012 11:05:58 -0600 Lee Mushel herbe...@centurytel.net wrote: If you're looking for a really interesting topic to read about, the development of an accurate ship-board clock is really fascinating! And it wasn't done overnight! If you have a few references on books to read, you shouldn't keep them for yourself ;-) Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] establishing your position w/o gps
If you want to try your hand at position determination in the pre radio nav days you can buy a studen sextent It's a low cost plastic instrument sells for about $60. Better ones start at $200 with $500 to $800 for a good one. But it required much pratice and training to outgrow the plastic instrument.I took the class.I think most anyone who wants to sail on the ocean had better take the class just in case their GPS fails. I know some one who had both his primary and backup GPSes fail and he was still a week from Hawaii. They had to revert to the old techniques from the 1700's Much of pre-GPS position determination is not about finding your latitude and longitude. That is a modern notion.What they did and what sailors still do is find a line of position. That means I am some place on this line but I don't know where on the line There are many ways to do this and they would work every method and find several lines. If they could see land they could shoot a compass bearing and draw a reciprocal bearing and know they were on that line. They would know the ship's heading and could estimate drift and know course over ground was parallel to that. They could always find a latitude line. Then if they did this right some of these lines would roughly intersect and they would know the position without need to know longitude. There were other methods to find lines that required an estimate of your speed and without clocks they resorted to chants and songs (jo ho, jo ho,...) As long as you sing the old pirate song at the same tempo every time you have a decent clock. Then you measure distance by tossing a big chunk of lumber overboard with a measured rope tied to it. The captains hated doing math by hand so they calibrated the rope by tieing knots at intervals so the natural unit was one arc minute at the equator and called it a knot. My buddy who was headed to hawaii put both GPSes in the oven in the galley and after three days was able to get one of them to work a few minutes a couple times a day. That was enough. But he said he was within maybe 15 miles of where he thought he was Basically your estimated course line intersected with a line of latitude gives you longitude. On Tue, Jan 24, 2012 at 8:50 AM, Azelio Boriani azelio.bori...@screen.it wrote: Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know. The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away. But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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. -- 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] establishing your position w/o gps
In addition to the moons of Jupiter, there was a method in direct competition with Harrison. It was the Lunar distance method. The Lunar distance method used the position of the Earth's moon against the zodiac as a clock. The term lunar distance was used because the navigator measured the angular distance from the moon to various stars to establish the moon's position and then the time was deduced from lunar position tables. Developing the lunar distance tables was part of the reason for establishing the Royal Observatory. John WA4WDL -- From: Chris Albertson albertson.ch...@gmail.com Sent: Tuesday, January 24, 2012 11:36 AM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] establishing your position w/o gps On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know.The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away.But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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] establishing your position w/o gps
Hi If you spend some time on the auction sites you can find some fairly good (though not brand name) sextants on the cheap. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Tuesday, January 24, 2012 12:48 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] establishing your position w/o gps If you want to try your hand at position determination in the pre radio nav days you can buy a studen sextent It's a low cost plastic instrument sells for about $60. Better ones start at $200 with $500 to $800 for a good one. But it required much pratice and training to outgrow the plastic instrument.I took the class.I think most anyone who wants to sail on the ocean had better take the class just in case their GPS fails. I know some one who had both his primary and backup GPSes fail and he was still a week from Hawaii. They had to revert to the old techniques from the 1700's Much of pre-GPS position determination is not about finding your latitude and longitude. That is a modern notion.What they did and what sailors still do is find a line of position. That means I am some place on this line but I don't know where on the line There are many ways to do this and they would work every method and find several lines. If they could see land they could shoot a compass bearing and draw a reciprocal bearing and know they were on that line. They would know the ship's heading and could estimate drift and know course over ground was parallel to that. They could always find a latitude line. Then if they did this right some of these lines would roughly intersect and they would know the position without need to know longitude. There were other methods to find lines that required an estimate of your speed and without clocks they resorted to chants and songs (jo ho, jo ho,...) As long as you sing the old pirate song at the same tempo every time you have a decent clock. Then you measure distance by tossing a big chunk of lumber overboard with a measured rope tied to it. The captains hated doing math by hand so they calibrated the rope by tieing knots at intervals so the natural unit was one arc minute at the equator and called it a knot. My buddy who was headed to hawaii put both GPSes in the oven in the galley and after three days was able to get one of them to work a few minutes a couple times a day. That was enough. But he said he was within maybe 15 miles of where he thought he was Basically your estimated course line intersected with a line of latitude gives you longitude. On Tue, Jan 24, 2012 at 8:50 AM, Azelio Boriani azelio.bori...@screen.it wrote: Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know. The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away. But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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. -- 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
Re: [time-nuts] establishing your position w/o gps
have you ever tried to measure an angular distance using a hand held instrument while standing on the deck of a moving boat in the open ocean? try it and you will see why they wanted a clock. You really can't measure an arc minute reliably we should expect about 15 arc minute accuracy if you are standing on a moving ship. A few very skilled people could do better. The moon moves what? about 10 degrees per day so in practical terms you can get time to about 30 minutes. But other sources of error would add to that. But still knowing even the hour is very good that puts you in the correct time zone On Tue, Jan 24, 2012 at 9:54 AM, jmfranke jmfra...@cox.net wrote: In addition to the moons of Jupiter, there was a method in direct competition with Harrison. It was the Lunar distance method. The Lunar distance method used the position of the Earth's moon against the zodiac as a clock. The term lunar distance was used because the navigator measured the angular distance from the moon to various stars to establish the moon's position and then the time was deduced from lunar position tables. Developing the lunar distance tables was part of the reason for establishing the Royal Observatory. John WA4WDL -- From: Chris Albertson albertson.ch...@gmail.com Sent: Tuesday, January 24, 2012 11:36 AM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] establishing your position w/o gps On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know. The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons of Jupiter and they could measure the time from local noon some even on Jupitor while a person back home did the same thing. Later when he got back home they compare notes and then know the difference in longitude. Good ocean going clocks were still centuries away. But in the 1500's they could only know the location after the fact when they returned -- 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. ___ 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. -- 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] establishing your position w/o gps
[snip] Then you measure distance by tossing a big chunk of lumber overboard with a measured rope tied to it. The captains hated doing math by hand so they calibrated the rope by tieing knots at intervals so the natural unit was one arc minute at the equator and called it a knot. Nope. A knot is a unit of velocity, not didtance. A knot is 1 nautical mile per hour A nautical mile is that distance, subtended at the earth's surface at the equator, by 1 arc-minute. If somebody tells you the ship was going 22 knots/hour they don't know what they are talking about. A knot/hour is an acceleration. I've only seen knots/hour used correctly once, in an inertial guidance system, for cross-track acceleration. My buddy who was headed to hawaii put both GPSes in the oven in the galley and after three days was able to get one of them to work a few minutes a couple times a day. That was enough. But he said he was within maybe 15 miles of where he thought he was Basically your estimated course line intersected with a line of latitude gives you longitude. -John ___ 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] establishing your position w/o gps by radio
Hi, Here's a little experiment I did while on last summer's Eclipse trip near Tahiti on a ship. I brought along my Sony short wave receiver and a Sony loop antenna. I went out on the deck and did a null and recorded the bearing to WWV, WWVH and JJY. I was able to read the null to within better than 5deg. I was hoping to hear a local LFMF broadcast station in the island group, but didn't get that far. That would have given me a better LOP (line of position) It wasn't extremely accurate but fun. Another time I was sailing to San Clemente Is off of San Diego and about midway my friend wanted to know how far we had sailed. I took out his pelorus (hand held compass) and a small AM radio and did a null bearing from KNX and KSDO which were at about right angles to each other. I later estimated I was well within a mile of our true position. Doug From: Bob Camp li...@rtty.us To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Tuesday, January 24, 2012 10:13 AM Subject: Re: [time-nuts] establishing your position w/o gps Hi If you spend some time on the auction sites you can find some fairly good (though not brand name) sextants on the cheap. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Tuesday, January 24, 2012 12:48 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] establishing your position w/o gps If you want to try your hand at position determination in the pre radio nav days you can buy a studen sextent It's a low cost plastic instrument sells for about $60. Better ones start at $200 with $500 to $800 for a good one. But it required much pratice and training to outgrow the plastic instrument. I took the class. I think most anyone who wants to sail on the ocean had better take the class just in case their GPS fails. I know some one who had both his primary and backup GPSes fail and he was still a week from Hawaii. They had to revert to the old techniques from the 1700's Much of pre-GPS position determination is not about finding your latitude and longitude. That is a modern notion. What they did and what sailors still do is find a line of position. That means I am some place on this line but I don't know where on the line There are many ways to do this and they would work every method and find several lines. If they could see land they could shoot a compass bearing and draw a reciprocal bearing and know they were on that line. They would know the ship's heading and could estimate drift and know course over ground was parallel to that. They could always find a latitude line. Then if they did this right some of these lines would roughly intersect and they would know the position without need to know longitude. There were other methods to find lines that required an estimate of your speed and without clocks they resorted to chants and songs (jo ho, jo ho,...) As long as you sing the old pirate song at the same tempo every time you have a decent clock. Then you measure distance by tossing a big chunk of lumber overboard with a measured rope tied to it. The captains hated doing math by hand so they calibrated the rope by tieing knots at intervals so the natural unit was one arc minute at the equator and called it a knot. My buddy who was headed to hawaii put both GPSes in the oven in the galley and after three days was able to get one of them to work a few minutes a couple times a day. That was enough. But he said he was within maybe 15 miles of where he thought he was Basically your estimated course line intersected with a line of latitude gives you longitude. On Tue, Jan 24, 2012 at 8:50 AM, Azelio Boriani azelio.bori...@screen.it wrote: Yes, the first real push was the Longitude Act (1714) and the Harrison's clocks. On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali att...@kinali.ch wrote: On Tue, 24 Jan 2012 11:04:08 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 20120124115848.312d60bd4fccce4f3e71c...@kinali.ch, Attila Kinali w rites: All this talk about telling the time using stars or the sun made me wonder how did people tell what position their telescopes had back in the days before GPS? Sailingships and trade was what pushed this. At the time of Columbus he was able to know his latitude within a few 10s of miles but even after returning to Europe he did no know how far around the world he had sailed. Was it 1/3rd or 2/3rds? They had no way to know. The problem was that on one had a clock that should keep time well enough. They used hour glasses on board ship for short duration time keeping but those were of no use on a longer ocean crossing. Later they discovered the idea of common view of the moons
Re: [time-nuts] establishing your position w/o gps
On Tue, Jan 24, 2012 at 10:31 AM, J. Forster j...@quikus.com wrote: Nope. A knot is a unit of velocity, not didtance. A knot is 1 nautical mile per hour A nautical mile is that distance, subtended at the earth's surface at the equator, by 1 arc-minute. If somebody tells you the ship was going 22 knots/hour they don't know what they are talking about. A knot/hour is an acceleration. You are using modern terminology. In the days when they tossed a real log overboard and measured time by singing a song. Issac Newton was still 100+ years in the future and no one new calculus or what acceleration was. Most sailors could not count to 100 out load and many could not even write their own name.I doubt they used the terms as precisely as we do now. History seems to only teach us about the top tier, the Royal Navy and their educated officers and the explorers like Cook and Magellan. Most were not nearly at that level of competence. Most captains followed cook book like directions and did not understand the theory. 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] establishing your position w/o gps
Then, as now, a knot is a unit of speed, not distance! If you counted 7 knots in a standard song, it was still speed. -John == On Tue, Jan 24, 2012 at 10:31 AM, J. Forster j...@quikus.com wrote: Nope. A knot is a unit of velocity, not didtance. A knot is 1 nautical mile per hour A nautical mile is that distance, subtended at the earth's surface at the equator, by 1 arc-minute. If somebody tells you the ship was going 22 knots/hour they don't know what they are talking about. A knot/hour is an acceleration. You are using modern terminology. In the days when they tossed a real log overboard and measured time by singing a song. Issac Newton was still 100+ years in the future and no one new calculus or what acceleration was. Most sailors could not count to 100 out load and many could not even write their own name.I doubt they used the terms as precisely as we do now. History seems to only teach us about the top tier, the Royal Navy and their educated officers and the explorers like Cook and Magellan. Most were not nearly at that level of competence. Most captains followed cook book like directions and did not understand the theory. 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] establishing your position w/o gps
The Lunar Distance method was not practical, but it was supported by the astronomers who felt that a mechanical contraption was beneath the art. Even Newton, who was the first head of the Longitude Board, would not consider the use of a mechanical clock. One argument from the astronomers was that astronomy could determine time but a clock could only keep time. John WA4WDL -- From: Chris Albertson albertson.ch...@gmail.com Sent: Tuesday, January 24, 2012 1:26 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] establishing your position w/o gps have you ever tried to measure an angular distance using a hand held instrument while standing on the deck of a moving boat in the open ocean? try it and you will see why they wanted a clock. You really can't measure an arc minute reliably we should expect about 15 arc minute accuracy if you are standing on a moving ship. A few very skilled people could do better. The moon moves what? about 10 degrees per day so in practical terms you can get time to about 30 minutes. But other sources of error would add to that. But still knowing even the hour is very good that puts you in the correct time zone On Tue, Jan 24, 2012 at 9:54 AM, jmfranke jmfra...@cox.net wrote: In addition to the moons of Jupiter, there was a method in direct competition with Harrison. It was the Lunar distance method. The Lunar distance method used the position of the Earth's moon against the zodiac as a clock. The term lunar distance was used because the navigator measured the angular distance from the moon to various stars to establish the moon's position and then the time was deduced from lunar position tables. Developing the lunar distance tables was part of the reason for establishing the Royal Observatory. John WA4WDL ___ 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] establishing your position w/o gps
But how do you untangle longitude and time? How do you know that you are looking exactly south (or north)? If I understand what you are asking, it's the same problem as navigating a ship without a clock. Classic navigation with a sextant needs a clock and sightings on 3 objects in the sky. Each sighting gives you a circle on the globe, or a line if you know roughly where you are. The lines form a triangle. The size of the triangle is an indication of the accuracy. You pick the objects so the triangle is roughly equilateral. http://en.wikipedia.org/wiki/Celestial_navigation You can get time from the moon, so in theory at least, that's an answer to your question. http://en.wikipedia.org/wiki/Lunar_distance_%28navigation%29 Years ago, when a friend was learning navigation, he was reading one of the old classic texts. There was a good story about the guy off the coast of England/Ireland who didn't trust his clock, so he did the calculations again assuming his clock was a bit fast and again with it slow. That gave him 3 parallel lines for each sighting. Anybody recognize that story? Longitude by Dava Sobel is a good read, especially for time-nuts. There is also a version with lots of good photographs. One of the techniques they actually considered before Harrison built good enough clocks was to derive time from Jupiter's moons. They knew enough to correct for the time shift due to speed of light delays as the Earth-Jupiter distance changed. (I don't know if they knew if was due to speed of light.) You can synchronize two clocks if both sites can see the same event in the sky, Occultations are often used for this. With modern technology, radio telescopes are very very good at this. In order to do VLBI, you need to know where the telescopes are located. With a big collection of data you can do least-squared fit type calculations to refine the location and clock calibration. -- 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] establishing your position w/o gps
Hi: The basic way to find your location anywhere in the world is to use a photo sensor. This is the method used on tagged fish. The light level is logged and time stamped probably using a watch crystal. When the fish is caught the logger data is read out. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/Brooke4Congress.html ___ 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] establishing your position w/o gps
For a rough determination; you are facing due south, or due north when the elevation of a celestial body stops increasing with time. The elevation is highest when the body is on the observer's local meridian. There are exceptions, for instance when observing a body below Polaris, then the body reaches the lowest elevation when crossing the observer's local meridian, but reaches its highest elevation twelve sidereal hours later. John WA4WDL -- But how do you untangle longitude and time? How do you know that you are looking exactly south (or north)? If I understand what you are asking, it's the same problem as navigating a ship without a clock. Classic navigation with a sextant needs a clock and sightings on 3 objects in the sky. Each sighting gives you a circle on the globe, or a line if you know roughly where you are. The lines form a triangle. The size of the triangle is an indication of the accuracy. You pick the objects so the triangle is roughly equilateral. http://en.wikipedia.org/wiki/Celestial_navigation You can get time from the moon, so in theory at least, that's an answer to your question. http://en.wikipedia.org/wiki/Lunar_distance_%28navigation%29 Years ago, when a friend was learning navigation, he was reading one of the old classic texts. There was a good story about the guy off the coast of England/Ireland who didn't trust his clock, so he did the calculations again assuming his clock was a bit fast and again with it slow. That gave him 3 parallel lines for each sighting. Anybody recognize that story? Longitude by Dava Sobel is a good read, especially for time-nuts. There is also a version with lots of good photographs. One of the techniques they actually considered before Harrison built good enough clocks was to derive time from Jupiter's moons. They knew enough to correct for the time shift due to speed of light delays as the Earth-Jupiter distance changed. (I don't know if they knew if was due to speed of light.) You can synchronize two clocks if both sites can see the same event in the sky, Occultations are often used for this. With modern technology, radio telescopes are very very good at this. In order to do VLBI, you need to know where the telescopes are located. With a big collection of data you can do least-squared fit type calculations to refine the location and clock calibration. -- 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] establishing your position w/o gps
On 1/24/12 9:48 AM, Chris Albertson wrote: If you want to try your hand at position determination in the pre radio nav days you can buy a studen sextent It's a low cost plastic instrument sells for about $60. That's the Davis Mark 3 (which is basically a copy of a lifeboat sextant). $50 from starpath.com (which also has the more expensive mark 15, and others) Or get a copy of Emergency Navigation by David Burch, and you can make your own instruments from materials close at hand. All the sight reduction tables and such are available online for free now. (although a paper copy is nice, and fairly cheap, being a government publication. ) Better ones start at $200 with $500 to $800 for a good one. But it required much pratice and training to outgrow the plastic instrument.I took the class. It's not that hard to learn yourself, once you get the right conceptual model. The trick is knowing how to use the sight reduction tables. (I figure that if your GPS has died, so has your calculator, so you'd better be able to do it with pencil and paper). I haven't gone to the extreme of calculating the trig functions by hand (wasn't that what Napier's wife did.. calculate log tables by hand during long sea voyages) I think you could probably do some interesting compass/straightedge/protractor kinds of geometric constructions to do sight reduction as well. Doing a fix on land, in one place, is pretty easy. (Much easier than standing on the deck of a boat that is moving). The only trick is having an artificial horizon that doesn't move.. A pan of liquid works nicely (molasses, thick motor oil, or corn syrup are your friends. Water is bad.. ripples in the least wind) Star sights are a bit trickier, just because the stars are dimmer and harder to find. And seeing the horizon at night is also tough. I think most anyone who wants to sail on the ocean had better take the class just in case their GPS fails. I know some one who had both his primary and backup GPSes fail and he was still a week from Hawaii. They had to revert to the old techniques from the 1700's And hey, you can learn while you're on the way, like Jack London did, on his way to Hawaii. Read the cruise of the snark (Project Gutenberg) Much of pre-GPS position determination is not about finding your latitude and longitude. That is a modern notion.What they did and what sailors still do is find a line of position. ___ 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] establishing your position w/o gps
On 1/24/12 9:46 AM, Attila Kinali wrote: On Tue, 24 Jan 2012 11:05:58 -0600 Lee Mushelherbe...@centurytel.net wrote: If you're looking for a really interesting topic to read about, the development of an accurate ship-board clock is really fascinating! And it wasn't done overnight! If you have a few references on books to read, you shouldn't keep them for yourself ;-) Dava Sobel's book is good. The Great Arc by John Keay also has useful information on this kind of thing. the Institute of Navigation (ION) has an $50 CDROM of almost 300 celestial navigation papers (http://www.ion.org/shopping/begin.cfm look down at the bottom) Lots about timekeeping, etc. in there. (got that one loaded on the iPad for long plane trips) ___ 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] establishing your position w/o gps
On 1/24/12 10:26 AM, Chris Albertson wrote: have you ever tried to measure an angular distance using a hand held instrument while standing on the deck of a moving boat in the open ocean? try it and you will see why they wanted a clock. You really can't measure an arc minute reliably we should expect about 15 arc minute accuracy if you are standing on a moving ship. A few very skilled people could do better. The moon moves what? about 10 degrees per day so in practical terms you can get time to about 30 minutes. But other sources of error would add to that. But still knowing even the hour is very good that puts you in the correct time zone you can do much better than that by looking for occultations (and they work with the new moon as well). If you know what day it is, you know about where the moon is, and you can look up in a table which stars get occulted when. Then you just watch through binoculars. I'd say you can get within ten seconds without much trouble, assuming you can find the star. ___ 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] establishing your position w/o gps
On 1/24/12 3:19 PM, J. Forster wrote: Is the USNO almana/ephemeris still published in hard copy every year? That had moon timing, etc. You can download pieces from the Astronomical Applications website at USNO. Or you can buy a copy of the Nautical Almanac for about $20 from a variety of sources. You could also download the pdf (but printing it would cost you more than the $20).. Amazon has it, for instance. http://www.usno.navy.mil/USNO/astronomical-applications/publications/naut-almanac will find it, but the GPO version is more expensive than the commercial versions.. ___ 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.
