Re: GMT and UTC
Earlier I wrote: The Explanatory Supplement to the Astronomical Almanac, mentions alternatives to atomic time under study that may offer improvements. (I don't have the book handy and cannot recall what they are. I will try to post a follow-up on Monday.) I believe that atomic timing technology is about fifty years old now... [...] Jim On pages 60-61 of the Explanatory Supplement to the Astronomical Almanac, is a discussion of modern timing technologies. 2.321 Quartz-Crystal Oscillators ... The performance characteristics may range from 10^-4 to 10^-13 in frequency stability per day. ... 2.322 Cesium Beam Standards ... laboratory cesium-beam frequency standards ... realize the second with the utmost accuracy (currently, 1.5 x 10^-14) and are, therefore, stable in the long term. ... 2.323 Hydrogen Masers ... The optimum stability reaches about 1 x 10^-15 for integration times of 1000 to 1 seconds. ... [S]ome hydrogen masers equipped with automatic tuning of the cavity and kept in temperature-controlled rooms have a long-term stability of the same order as the best cesium standards. ... 2.324 Rubidium Vapor Cells The rubidium clock is an appropriate device when a relatively low-cost clock is needed that has better stability than a quartz crystal clock. The rubidium clock can reach a stability of 1 x 10^-13 per day under the best conditions, but is subject to temperature- and pressure-induced frequency variations. Ringer et al. (1975) describe the design and performance of a clock for the GPS satellites. This clock has achieved stability of 2 x 10^-13 per day. 2.325 Mercury Ion Frequency Standard The mercury-ion frequency standard uses ions that are confined in a small region of space by an electromagnetic field trap. Thus the particles can be observed without having them collide with the walls, which would disturb the atomic resonance. The mercury-ion isotope Hg-199 has an extremely narrow microwave resonance line at 40507 MHz. Although this type of frequency standard should be a large improvement over the cesium standard, it has an unfortunately low signal-to-noise ratio, resulting in limited short-term stability. However, the long-term stability is very good, since integration can take place over a number of days (Winkler, 1987). I suppose I was incorrect to call these alternatives to atomic timing. Quartz is molecular; the maser is ultimately atomic in nature (or perhaps molecular, I'm not sure); and the others are all atomic. But they are alternatives to atomic cesium clocks. Jim --- -- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric| Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | --- -- Have you noticed how the hole in the ozone layer has grown progressively larger since rap got popular? -- Dave Barry
Re: Sunset times (was: GMT and UTC)
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] wrote: snip ...as the time of sunset varies by as much as 6 hours from solstice to solstice (here in Michigan). end snip Hmmm... can someone help me out? A quick check of my astrolabe, with a plate for St. Paul, MN, gives sunset at about 1618hrs for the winter solstice, and about 1943 for summer - about a 3 1/2 hr variance. Am I missing something? Mike Blackwell For Detroit (assuimg EST is the time zone) xephem computes Limb 6/21/1999 4:55:05 EST: RiseTm SetTm HrsUp Sun 4:55 20:13 15:18 Limb 12/21/1999 4:55:05 EST: RiseTm SetTm HrsUp Sun 7:57 17:03 9:06 which agrees with your astrolabe computations. My guess is he was thinking of a six hour daylight delta. Jim --- -- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric| Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | --- -- Your emotions are often a reverse indicator of what you ought to be doing. -- John F. Hindelong
Re: Slowing Rotation
I stand corrected, if the Moon had greater gravity than the sun, the Earth would orbit the Moon instead of the Sun. Troy They all orbit each other.The path of the Moon relative to the sun is, however, *always* concave to the Sun. In that geometrical sense the Moon could be considered to be orbiting the Sun. Les Cowley Atmospheric halos http://dspace.dial.pipex.com/lc/halo/halosim.htm
first italian sundial mail list on internet!
GNOMONICA Storia, Arte, Cultura e Tecniche degli Orologi Solari Bollettino della Sezione Quadranti Solari dell' U.A.I. con la collaborazione degli Gnomonisti Italiani Redazione - Nicola Severino, Via Lazio, 6 - 03030 Roccasecca Stazione (FR) Italy- Phone 0776 - 56.65.08 - e-mail: [EMAIL PROTECTED] WEB pages: http://staff.sunrise.it/gnomonica/ For free subscription on first italian sundial mail list send the following message subscribe to: [EMAIL PROTECTED] Dears All, I am very pleasured to write you that the firts italian mail list on sundial have been started. The subscription is totally free and his functions are eguatl to this sundial list. Only, we used the italian language for message. If you wish a subscription, please, write a message subscribe to address [EMAIL PROTECTED] for sending italian message (or short english message): [EMAIL PROTECTED] Thank you. We hope you are interested in our list. Yours sincerely Nicola Severino
Re: Heliochronometers: Equation of Time
My apologies for such late input to this thread, I have been a little behind in my e-mail! I encountered many of these problems and the same questions when designing my Analemmic Equatorial sundial ( http://netnow.micron.net/~petes/sundial ). I hope the following will help. Luke Coletti wrote: I have found the best method of correcting for the periodic variability of the EoT relative to the calendar is to take the EoT as a four year average. Tom Semadeni wrote: How do you do that? Do you pick a 12 month year which straddles the mid point between two leap years, like Jun 30, 97 to Jun 30, 98? The method I used to derive "average" date points for my analemmic gnomon, and a table of the resultant values, may be found at http://netnow.micron.net/~petes/sundial/dialcalc.htm . As others have stated, this does not affect the shape of the analemma, just the location of the date's position on the analemma. This normally does not affect the time accuracy of the analemmic sundial, except near the solstices; a 1 day error near the winter solstice would affect the indication of time by 1/2 minute . Luke Coletti wrote: The temporal variability, as has been discussed in earlier threads, is chiefly due to the phase relation between obliquity and eccentricity as caused by the precession of the equinoxes and the shifting of perihelion. The magnitude of obliquity and eccentricity changes too but on a slower time scale. I prepared several graphs last year, prior to the NASS conference, using Luke Coletti's Solar Calculator program ( http://www.gcstudio.com/suncalc.html - Thanks Luke! ) and Excel to show how the effects of changing obliquity and eccentricity of the Earth's orbit may be expected to change the accuracy of my sundial long-term. The graphs show the necessary shape of the analemmic gnomon for the years 2000 BC, , 2000 AD, 4000 AD and 6000 AD. I found them rather interesting, and so I hope you will forgive me for attaching them to this e-mail. Thanks. Pete S. ( http://netnow.micron.net/~petes ) Attachment converted: MAC Hard Disk:Millen.gif (GIFf/JVWR) (000127E6)
proposed sundial
We are in the process of designing a horisontal sundial for the southern hemisphere with a gnomon height of over 40m. We would be grateful to receive any response with regard to any of the following: -common errors to avoid during concept, detail drawing and construction stages; -flagging of any issues concerning the size shape material of the gnomon/style; -any other information that would help ensure that the practicalities of designing a sundial on this scale are met. Pictures of the proposal are available as jpeg files. Pieter.
RE: sunset times
sorry...It should have read the period of daylight varies as much as 6 hours from solstice to solstice. Troy ([EMAIL PROTECTED]) [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] wrote: snip ...as the time of sunset varies by as much as 6 hours from solstice to solstice (here in Michigan). end snip Hmmm... can someone help me out? A quick check of my astrolabe, with a plate for St. Paul, MN, gives sunset at about 1618hrs for the winter solstice, and about 1943 for summer - about a 3 1/2 hr variance. Am I missing something?
Re: proposed sundial
Hi Pieter, You might want to check out the dial of one third the magnitude at: http://sciencenorth.on.ca/AboutSN/polaris/index.html If you send me some .jpegs, I could comment on your huge project with more focus. Cheers, Tom Pieter M DeKock wrote: We are in the process of designing a horisontal sundial for the southern hemisphere with a gnomon height of over 40m. We would be grateful to receive any response with regard to any of the following: -common errors to avoid during concept, detail drawing and construction stages; -flagging of any issues concerning the size shape material of the gnomon/style; -any other information that would help ensure that the practicalities of designing a sundial on this scale are met. Pictures of the proposal are available as jpeg files. Pieter.
