People might be interested in the book "The Sun in the Church" by Heilbron. It's about using meridian lines in cathedrals for solar measurements. http://www.math.nus.edu.sg/aslaksen/teaching/heilbron.html
> 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, >> Playd 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
