How the Brightness of the Moon is Measured

The brightness of a full moon has inspired centuries of creation myth, poetry and even vampire and werewolf mini series and movies.  Yet few people know that the shining moon actually reflects less light than the planet Venus. The albedo of the moon,  it’s reflective brightness, is considered to be low.  To understand more about why this is so, one has to investigate albedo itself.  There is more than one kind of albedo, or reflecting ability, in regards to the moon.

The term Albedo comes from the Latin term for white. It simply describes the solar radiation of light wavelengths reflected by any given surface, or body. To see why the moon is seen as so bright, one needs to clearly understand that as a mirror to the sun, it shines more brightly to human eyes than it is measured to be by more than one albedo reference.

Bond albedo does not refer to 007, but to the moon’s albedo rating of just plain 7 (seven). This refers to the fraction of the total light energy hitting the moon from the sun and sent off in all directions.  Bond albedo has nothing to do with perceived brightness, however.  That type of albedo is called visible geometric albedo.  It is the brightness to the human eye when viewed from earth.

Scientists need only to look at the actual surface of earth’s famous howl inspiring satellite to learn why the Bond albedo is so low compared to other planetary bodies in the local solar system.  They measure the amount of actual energy which is diffused upon the lunar surface.

Visible geometric albedo is measured within a band of visible wavelengths.  As the name implies, visible light is seen as very bright, especially at full moon, to all earth inhabitants.  Physical variations of planetary surfaces are investigated with this kind of measurement. This is the kind of luminous glow that so influences those earth tales of life and death all earthlings have come to create.

Another measure of albedo is gathered by studying the geometry of peaks, valleys, and plains on the moon.  This is called normal or visual normal, albedo. Lighter areas that are high up, such as peaks and crater rims reflect more luminosity than low lying craters and the large moon areas, or plains, called maria. 

It is fascinating that the moon then appears so brightly to human beings.  With the overall albedo being at just a seven, it is amazing that so much of human and indeed, all earth life is influenced by the beautiful moon.  Migrations, menstruation and much of earth’s biology and tides are influenced by it as we know,  as well as all of the humanities,  horror stories, and even Emo teenage tales of romance and angst.