That's still around one part in 10^8 over a year, not quite 6 decimal places of days, but very close!
Sent from my iPhone On Mar 26, 2011, at 11:04 AM, Brooke Clarke <bro...@pacific.net> wrote: > Hi: > > It turns out that because of "seeing" you can not determine meridian crossing > to better than about 5 arc seconds (5 * 55 ms of time). (The exception is > for locations at high elevations or in space.) I've heard that modern CCD > cameras can image sections of the sky and fit the image to a very good star > catalog thus averaging the seeing of hundreds of stars and get orders of > magnitude better time/space resolution. > http://www.prc68.com/I/StellarTime.shtml > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > > > Kevin Karney wrote: >> Brent >> If you measure the transit of a star (or any celestial body) through the >> meridian again and again over many years with telescopes that can >> distinguish less than 1 second of arc, then it's perfectly possible. >> Remember 1 second of time = 15 seconds of arc. These measurements - now done >> automatically - have been done for years by using transit telescopes to >> take photographs of the stars and then by taking measurements off the photo >> plates. >> >> Even without sophisticated instruments, surprising accuracies were >> obtained... >> >> >>> Malik Shah the grandson of Toghril Beg, the founder of the Seljuk dynasty >>> ruled the city of Isfahan from 1073 AD. His vizier Nizam-ul-Mulk invited >>> Omar Khayyam to Isfahan, to set up an observatory. Other leading >>> astronomers were also invited to work at the observatory and for 18 years >>> Omar Khayyam led the scientists and produced work of outstanding quality. >>> It was a period of peace during which the political situation allowed >>> Khayyam the opportunity to devote himself entirely to his scholarly work. >>> During this time Khayyam led work on compiling astronomical tables and he >>> also contributed to calendar reform in 1079. Khayyam measured the length of >>> the year as 365.24219858156 days, we know now that the length of the year >>> is changing in the sixth decimal place over a person's lifetime. It is also >>> outstandingly accurate. For comparison the length of the year at the end of >>> the 19th century was 365.242196 days, while today it is 365.242190 days. >>> >> Omar Khayyam was a real polymath - a notable astronomer, mathematical and >> poet. He famously wrote .... >> >> >>> A Book of Verses underneath the Bough, >>> A Jug of Wine, a Loaf of >>> Beside me singing in the Wilderness -- >>> Oh, Wilderness were Paradise enow! >>> >> and (especially for us gnomonists) >> >> >>> For in and out, above, about, below, >>> ’Tis nothing but a magic shadow-show, >>> Play’d in a box whose candle is the Sun, >>> Round which we phantom Figures come and go >>> >> Best regards >> Kevin Karney >> Freedom Cottage, Llandogo, Monmouth NP25 4TP, Wales, UK >> 51° 44' N 2° 41' W Zone 0 >> + 44 1594 530 595 >> >> On 26 Mar 2011, at 13:57, Brent wrote: >> >> >>> It's amazing that someone was able to calculate these >>> numbers out to 6 decimals. Is that done by some type of >>> observation or is it mathematics? >>> >>> How could you possibly measure something like that? >>> >>> >>> >>> On 3/25/2011 1:14 PM, Kevin Karney wrote: >>> >>>> Nothing is constant in the heavens ! >>>> The 'tropical' year (from equinox to equinox) is 365.242190 days >>>> The 'sidereal' year (fixed star to fixed star) is 365.256363 days >>>> The 'anomalistic' year (perihelion to perihelion) is 365.259636 days - >>>> cycling over a period of some 21000 years >>>> (values for 2009 from Astronomical Almanac) >>>> But these are mean values having averaged out the effects of nutation (the >>>> wobbling of the Earth's axis) and various other effects. >>>> >>> --------------------------------------------------- >>> https://lists.uni-koeln.de/mailman/listinfo/sundial >>> >>> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >> >> >> > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
