Doug,
1. You could do what the Egyptians and the Greeks did 1500 years earlier. Use a mural quadrant in the meridian to establish the greatest and least altitude of the noon sun ( from this you could calculate the orbital inclination and your latitude) and mark the mid altitude. You then sit and count the days between each instant that the midday sun attains this altitude in spring. You could refine the measurement by noting the altitude for several days and interpolating to determine the moment of equinox. After just a few years you would determine that the length of the tropical year is about 3651/4 days and the longer you observed the more precise this figure would become. You could also use an equatorial ring to make the observations which should make direct observation of daytime equinoxes possible but this would be more difficult to construct accurately. 2. If you were equipped with a transit telescope and a means of recording transits to the second, then you could adopt the same procedure as the ancients but your results would converge more rapidly on the true length of the tropical year. Best wishes, Geoff On 18 February 2017 at 18:07, Douglas Bateman < [email protected]> wrote: > Given that this group has experts on the calendar and the earth’s orbit, I > have a couple of questions. > > 1. Assuming that I was living a 1000 years ago, and had unlimited time > watching the sun and stars (and *without prior knowledge*) how would I > notice that each year was growing by about a quarter of a day? > > 2. Assuming that in 1850s I had access to a good transit telescope, and a > reasonable clock (daily errors about 1 second a day), how would I refine > the quarter of a day into several decimal places? > > These questions have been prompted by a debate in horological circles that > the astronomers in the 1800s could have benefited by having a clock that > was better than a second a month. My own view is that the 1 second a day > was adequate because the clock is only put to use for *differential* > measurements in time between frequent ‘clock stars’ each night and the > transits of interest. Neglecting cloudy periods for the sake of argument. > > I look forward to receiving good advice. > > Regards, Doug > > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > >
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