Comparing the Albedo of Venus and the Moon

The planet Venus has the highest albedo in the solar system, yet the moon appears brighter to people on earth because it is so much closer than Venus.

Albedo refers to the reflected brightness of a surface, or planetary body, in this case.  Albedo comes from the Latin word Albus, meaning white.  Think of the term “Albino” to remember the whiteness of an albedo.

The moon has an averaged albedo of about seven to twelve percent, which is measured by averaging the three types of albedo that astronomers use for frame of reference.  The first of these is Bond albedo, which measures overall radiated electromagnetic energy. The second is called geometric albedo. This geometric measurement is based on a ratio between actual illumination to an ideal brightness, (as upon a flat reflecting disk). The visual geometric albedo refers to light measurements of the surface within the visual spectrum.  Because these three measurements can vary widely, it can be confusing to measure the albedo of the moon and Venus.

Venus has an albedo of ninety in the Bond Albedo and sixty seven in the visual geometric albedo. So Venus is very bright. Known for centuries as the morning and evening star, Venus can be seen near the horizon as the brightest “star” in the sky.

It is so bright because Venus is covered with churning clouds of greenhouse gasses. Venus, then,  reflects quite a lot of light into space. Because Venus spins slowly on her axis, it is believed that this may contribute to the heavy atmosphere and constant cloud cover. Climatologists study Venus, then, to learn how greenhouse gases affect a planetary body. Given a few million more years, as the sun expands, Earth’s inevitable fate will be as scorching hot as Venus is presently.  But for now scientists are just concerned about greenhouse gases on Earth and trapped heat which is affected by Albedo.

The moon has a dark surface, but it is a mirror reflecting the brightness of the sun.  Depending upon time of day, phase of the moon and position of the observer, the moon varies in brightness. The moon is of course, the nearest celestial object to earth. Venus, on the other hand, is more than 450 times farther away from us. One can imagine that were Venus any closer, the reflected light would be quite blinding!

Both of these celestial objects are renown for their brightness and beauty.  Venus is of course named for the goddess of beauty and love, also known as Aphrodite. And the moon is named for Luna, the Roman name of the bright and lovely, Greek goddess Selene.