use UTC!
libration lon:
lat:
position angle of axis:
sub-sun lon:
lat:
distance in km:
sub-sun point
sub-earth point
Exclude position angle
Exclude shadow
Horizon: equator sub-earth lon/sub-sun lat's error is less than 20 arc min; sub-earth lat/sub-sun's lon/position angle of axis
eror in less than half
arc min between 1900-2050 (compared to de421).