Expert: Philip Stahl - 10/12/2008

Question
How did ancient astronomers figure out it took 365 & 1/4
days to travel around the sun 1 year. Would it not have
been easier to just add a little extra time to each day
than add an extra day every 4 years.I am confused and do
you know who set out the common calendar as we know it. I
presume it was an astronomer as it seems to be linked with
the moon phases.Thank you in advance.

Answer
Hello,

Your question demonstrates it is possible to ask something that (apparently) is relatively simple - but which in fact is enormously complex and requires a lengthy response. To really do justice to it would consume more megabytes than a small pamphlet, and more time than I currently have available.

Anyway, in regard to the first (and most straightforward) part, most scholars of early astronomy believe the Chinese were the first to determine the length of day at 365 1/4 days as early as the 12th century.

This would not be a stretch at all, if they were able to reliably keep track of the positions of specific stars they recognized through a year. That would mean tracking the star's change in position until such date it returned to as close to the original position as possible. The rest would be merely simple counting. (And we know the Chinese also invented the first "computer"  known as an abacus)

The fact that the Chinese astronomer Shih Shen had amassed a star catalog of 800 entries as early as 350 BCE, indicates this was certainly plausible.

As to your question of whether it would be preferable to "add a little bit of extra time" each day, this is not so easy as it seems. For one thing, you'd have to have a reliable means to keep account of this extra time, e.g. as it is aggregated. For another, it would make day to day calculations (especially in an era where people had no computers or calculators with long storage capability) very dicey to say the least. So, easier to simply add 0.25 year every four. More manageable - and once everyone knows and agrees to the rubric there is no problem.

To find out more about the details of who set out the common calendar I suggest going to this site - and clicking the links where you detect the names or issues of interest.

http://www.geocities.com/researchguide/time.html

Also see:

http://www.webexhibits.org/calendars/calendar-roman.html

(part of the same site)


Also doing the searches as they come to mind. This is a lot more efficient than me trying to prepare a small treatise on the history of the calendar starting from the Roman Republican Calendar (used from 70 BCE, with 10 months - the last four of which were: September, October, November and December - corresponding to our own) to the Julian Calendar (with 12 months averaging 30.5 days each) to the Gregorian Calendar introduced in 1582 - which had to make a 10 day "correction" by proclaiming October 4, 1582 actually October 15, 1582.

Now, are you really confused?

Anyway, no problem.  Simply go the links referenced and also use any or all of the above info for googling, e.g. "Gregorian Calendar".  
Good luck, and have fun!