Albedo, ratio between the amount of light a body reflects or scatters and the amount of light that is absorbed. A body that has an albedo of 0.3, for example, reflects or scatters three-tenths, or 30 percent, of the light that falls on it while absorbing the rest.

Various physical characteristics of a body determine its albedo. The earth’s moon has a rough surface that absorbs most of the sunlight that strikes it. The moon, therefore, has a low albedo of 0.12. The planet Venus has a highly reflective cloud layer, which gives the planet an albedo of about 0.65, the highest of any planet in the solar system. The earth’s albedo is about 0.37.

Scientists measure two specific kinds of albedo: bond albedo and normal albedo. Bond albedo is the ratio between the amount of energy that a body reflects and the amount of energy that falls on the body. It is used to keep track of the energy balance of a body, or how much energy a body is gaining or losing.

Normal albedo is the ratio between the amount of light that a surface reflects straight up and the amount of light that falls straight down on the surface. Depending on the composition of the surface, the normal albedo of a surface for different wavelengths of light can be different. By looking at the normal albedo of different wavelengths of light, astronomers can infer the chemical composition of the surface.