Originally from ticket #4821.
I am using SNP 4.5.2. on an older iMac. How is the image of the
crescent moon determined and displayed when the moon is about 12 hours
from new phase. When I calculate the position angle of the bright
limb, should that point coincide with the center of the illuminated
edge of the moon? I am considering topocentric, and measuring from
the grid in "Surface Guides".