Question: What is the algorithm for calculating Heliocentric Julian date from a given Julian date and object RA/Dec? I would like this for a variable star application I’m writing. — James
Answer: I would start with the online calculator provided by the British Astronomical Association. If you are adventurous and you can program in Python, you might want to try the PyAstronomy routine for this calculation (which is, I believe, a port of the original IDL routine which does this calculation). Finally, if you would like to do the calculations by-hand, check-out the Wikipedia page on Heliocentric Julian Date.