← All posts healpix coordinates 2010-06-23 astrophysics Download source Contribute Healpix considers latitude theta from 0 on north pole to pi south pole, so the conversion is: theta = pi/2 - latitude longitude and phi instead are consistently from 0 to 2*pi with zero on vernal equinox (for ecliptic ). zero in the direction from Sun to galactic center (for galactic )