I am experimenting with the Python library PyEphem for astronomy, and I am trying to recreate/understand some of the basic calculations there.
There is a function called separation that, given two planets and a date/time, it calculates the separation (angle) between those 2 planets with respect to their "x" projection in a plane.
So for 2018/1/1 for planets Mercury and Mars, we have:
import ephem import math mercury = ephem.Mercury('2018/1/1') mars = ephem.Mars('2018/1/1') s1 = ephem.separation(mercury, mars) print(math.degrees(s1))
But if I wanted to calculate this without the separation function, then I think that the calculation would be as simple as the "right ascension" of 1 minus the "right ascension" of the other:
math.degrees(mercury.ra) - math.degrees(mars.ra)
Why are the angles different? Since I am not including a latitude and longitude of the observer, all the calculations are supposed to be geo-centric, according to PyEphem.
Is anybody familiar with the calculations going on behind PyEphem, or another library with built-in ephemeris that can produce consistent results for separation?