At the moment I'm trying to put together a little spreadsheet calculator. The idea is to roughly indicate the position of an object based on a viewing time and date.
To do this I need to work out how RA coordinates are is calculated from the J2000 epoch.
From what I understand RA is calculated from an equinox at a given point in time. Throughout the months of the year the object gains time behind the Sun and ends up in the same position behind Sun 12 months later.
What I need to know is from which equinox (if it is an equinox) is the RA from J2000 epoch calculated.
Is it the northern hemisphere vernal equinox (roughly March 21 2000)?
Or is it not an equinox and January 1st 2000 12:00 Terrestrial Time?
Slightly confused, if anyone could shed some light on this it would be appreciated.