# hcrs_to_hgs¶

sunpy.coordinates.transformations.hcrs_to_hgs(hcrscoord, hgsframe)[source] [edit on github]

Convert from HCRS to Heliographic Stonyhurst (HGS).

HGS shares the same origin (the Sun) as HCRS, but has its Z axis aligned with the Sun’s rotation axis and its X axis aligned with the projection of the Sun-Earth vector onto the Sun’s equatorial plane (i.e., the component of the Sun-Earth vector perpendicular to the Z axis). Thus, the transformation matrix is the product of the matrix to align the Z axis (by de-tilting the Sun’s rotation axis) and the matrix to align the X axis. The first matrix is independent of time and is pre-computed, while the second matrix depends on the time-varying Sun-Earth vector.