Air Signs. The mental or intellectual signs: Gemini, Libra, Aquarius. Considered collectively, sometimes termed the Air asterism.
Albedo. Literally, whiteness. A measure of the reflecting power of a planet, in ration to its absorptive capacity; expressed in a figure which represents the amount of light reflected from an unpolished surface in proportion to the total amount of light falling upon it.
The albedo of the Moon and Mercury is 7; Venus 59; Earth 44; and Mars 15.
Thus, the changeable character manifested by Moon and Mercury is seen to be connected in some way with their low reflective capacity.
An entirely different set of Lunar characteristics comes of the fact that as the Moon approaches an opposition to the Sun its surface temperature rises some 70-odd degrees above boiling point, and in consequence it emits a wide band of infra-red frequencies that are several times more powerful than any of the rays it reflects from the Sun. During the first few minutes of a Lunar eclipse, the surface temperature falls to a sub-zero level and the infra-red emanation ceases.
The dimly-lit surface of the Moon at the Lunation is due to light reflected back from the Earth, which with its high albedo would appear to the Moon-dweller as four times larger and many times brighter than the Moon as seen from Earth.
There are some indications that Jupiter emits a ray of its own in addition to its reflected ray, but astrophysicists are not as yet in accord on that point.