Micro moon versus macro moon: Brightness and size

TL;DR

This paper derives theoretical expressions for the brightness and apparent size of full moons at lunar apogee and perigee, quantifying their differences and confirming observed variations such as super moons.

Contribution

It provides the first theoretical derivation of lunar brightness and size variations at apogee and perigee, quantifying their differences.

Findings

Full perigee moon is about 29% brighter than apogee moon.

Full perigee moon is about 14% larger than apogee moon.

Derived expressions match reported observational data.

Abstract

The moon, moonlight, phases of the moon and its relatively simple recurring cycle has been of interest since time immemorial to the human beings, navigators, astronomers and astrologers. The fact that its orbit is elliptical as well its plane is inclined with the plane of rotation of the earth gives rise to new moon to full moon and solar and lunar eclipses. During the phase of the full moon, the luminous flux and its apparent size will depend on its distance from the earth. In case it is at farthest point known as lunar apogee causes smallest full moon or micro full moon and if it is closest to us termed as lunar perigee will result in macro full moon, also known as super moon, a term coined by astrologer Richard Nolle in 1979. The theoretical expressions for the lunar luminous fluxes on the earth representing the power of lunar light the earth intercepts in the direction normal to the incidence over an area of one square meter are derived for two extreme positions lunar apogee and lunar perigee. The expressions for the apparent sizes of full moons corresponding to said positions are also mentioned. It is found that full perigee moon is about 29 percent brighter and 14 percent bigger than the full apogee moon consistent with the reported values.