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
