Q: New Year

[AmitaSarin at aol.com]

Now that we have decided that it is perfectly appropriate to discuss
astrology/astronomy on Indology, I'd like to continue by restating what I
have learned from the discussion thus far in simple language (in reln. to my
question on festivals).
Some festivals in India are based on the cycles of the moon and their dates
change from year to year on the western calendar. 
 Festivals that have a constant date are based on a sort of solar/sidereal
system ie. the entry of the sun into certain stellar constellations.  Pongal,
Lohri, Makara Sankranti etc. which are celebrated around the 13th-14th of
January coincide with the sun's entry into the constellation of Capricorn.
 Once upon a time this event coincided with the sun being over the tropic of
Capricorn (winter solstice), but because of precession (slippage) this is no
longer the case.  Currently, the winter solstice is on December 23rd, the
shortest day of the year.  (However, according to at least one Hindu temple
calendar that I have seen, Uttaraayana, or the sun's journey to the north,
still begins on the 14th of January, which is apparently still considered the
winter solstice according to some traditions).
April 13th, when the sun enters the constellation of meshasamkranti, is
celebrated as New Year by many communities all over India.
March 21st, the spring equinox, when days and nights are equal, sort of
coincides with Navroze, the Persian New Year.  However, from what I have
understood from Mughal sources, this was also calculated according to the
sidereal system, and was based on the time the sun entered the constellation
of Aries.  As far as I know, no Hindu festivals are based on the spring
equinox.
I beg your indulgence for the above.  This discussion has refreshed and
deepened my understanding of the subject.   I request the astronomy/astrology
gurus to correct my mistakes.  Many thanks, 
Amita Sarin