Lunar parallax and Indian astronomy

mgansten at mgansten at
Wed Mar 26 09:54:40 UTC 1997

Here is a question for all pancaanga-wallahs on the list: Due to the
relative closeness of the Moon to the Earth, the Moon's apparent zodiacal
longitude will sometimes differ by anything upto one degree depending on
whether the calculation is based on the centre of the Earth or on any given
location on the Earth's surface. (That, at least, is how I have understood
the term "lunar parallax".) Obviously, this could affect the time of the
Moon's entry into a given nak.satra by a couple of hours. So what did the
ancient Indian astronomers do -- did they base their calculations on the
Moon's position as seen from the place of observation, or did they use
formulae involving the Earth's centre? And what is common practice today?

I would greatly appreciate any elucidation from those who know their
Suryasiddhanta (or whatever) better than I -- or even just a pointer to
which person/s or book/s I might consult. 

Thanks in advance,
Martin Gansten

mgansten at

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