Distance from the Sun - the further from the sun, the less light an object recieves. The amount is the inverse of the square (i.e. 4 becomes 1/4) of its distance from the sun.

Angular size - the size of an object as seen by an observer, not the actual size.

Albedo - from "albus" or white. The ratio of light reflected off of the surface. Zero is no light, one is all light. All fall somewhere in the middle as nothing is perfectly reflective or absorbative. Magical albedo is the ratio of magic instead of the ratio of light.

Phase - The proportion of the body that is lit in the sky and can be seen from Earth.

These four quantities are all independent of each other.

Interference - magic is influenced by magic reflected by other objects in the sky. Constructive interference is when two or more sources inhance each other. Destructive interference is when the opposite happens. If objects appear to be 90 degrees apart, they do not interfere.