These are chat archives for astropy/astropy

29th
Jul 2018
matrixbot
@matrixbot
Jul 29 2018 16:53
akk on Freenode Hi -- I have a program where I'm plotting Mars' retrograde loop and calculating things like opposition and closest approach
akk on Freenode trying to calculate opposition by doing mars = get_body('mars', cur_time); sun = get_body('sun', cur_time); elongation = (mars.ra - sun.ra) and use that to determine opposition
akk on Freenode and PyEphem gets the right answer, but AstroPy sees it happen on the wrong day, and it also shows the planet approaching and receding several times during the month.
akk on Freenode I'm wondering, does get_body(name, time) calculate from some specific point on earth even though I deliberately don't specify one, so I'm seeing parallax issues?
matrixbot
@matrixbot
Jul 29 2018 18:27
akk on Freenode Any advice on calculating opposition/elongation? I seem to be getting the wrong values from get_body('mars', cur_time).ra - get_body('sun', cur_time).ra.
akk on Freenode I'm getting apparently wrong answers for distance too, so I wonder if get_body is measuring from some moving point on earth.