ecn-ec:ecn-pc:ecn-ed:vu@pur-ee.UUCP (09/02/83)
My answer to the question is in net.wanted .( I typed 'f' ) Hao-Nhien Vu (pur-ee!vu, soon pur-ee!norris)
abdali@teklabs.UUCP (09/16/83)
The division of a year into 12 months is not by convention, but is
forced on us by the definition of year and month. Basically, the
month is derived from the motion of the moon and the year from the apparent
motion of the sun on the ecliptic. Next to the daily apparent
motion of the sun, the two most noticeable recurrent phenomena to provide
units of time have historically been: 1) The phases of the moon
and 2) the seasons. The cycle time for these are respectively used to
define the month and the year. It so turns out that a year contains
(very nearly) 12 months.
This is a very simplified explanation. To be more rigorous, one
needs to distinguish between various kinds of year (e.g., solar,
sidereal) and month (synodal, etc.). Most textbooks of astronomy
give the detailed definitions. There is an excellent book giving the
historical development of calendars, but its title escapes me now.mark@cbosgd.UUCP (09/18/83)
Actually, if we went by the moon, we'd have 13 months/year. It isn't quite exact, but it's amazingly close. I wonder how we got 30 and 31 day months out of a 28 day lunar cycle?
dave@utcsrgv.UUCP (Dave Sherman) (09/19/83)
The Jewish calendar is a lunar calendar. The months are 29 or 30
days, and there are normally 12 months in a year. However, in seven
out of every nineteen years, there is a 13th month, adding another
29 or 30 to the normal 354. Every 19 years it comes back in sync with
the solar calendar. (The Jewish holidays come out this year on the
same days they did in 1964 and 1945, give or take one day.)
Dave Sherman
--
{cornell,decvax,floyd,ihnp4,linus,utzoo,uw-beaver,watmath}!utcsrgv!lsuc!davebill@utastro.UUCP (09/19/83)
ews. Bill Jefferys 8-% Astronomy Dept, University of Texas, Austin TX 78712 (Snail) ihnp4!kpno!utastro!bill (uucp) utastro!bill@utexas-11 (ARPA)