Monday, April 26, 2021

The albedo in Astronomy

The albedo in astronomy is the fraction of light that is reflected by a celestial object that does not shine with its own light, such as a planet or an asteroid.

The albedo varies between zero when all the incident light is absorbed and one when there is total reflection. The albedo of an object depends on many factors (for example the composition and surface morphology or the presence of an atmosphere) and also depends on the surface region we are observing. For example, the albedo of the Earth will vary if we are above a desert (which reflects 25% of the incident sunlight) or above snow-covered regions, which instead have an albedo of 0.9.

Studying the albedo of the various objects in the Solar System can therefore provide us with important clues about their physical characteristics.

Among the eight planets, the one with the highest albedo is Venus, which reflects about 70% of the sunlight that hits it. This is due to the highly reflective clouds found in its atmosphere.

For comparison, the average albedo of the Earth is 0.30, while the Moon reflects only 7% of the incident light.

The object with the highest albedo in the entire Solar System is Enceladus, a moon of Saturn (shown in the image). In fact, this reflects 99% of the light that hits it!

This high reflectivity is explained by the composition of the satellite. The instruments of the Cassini spacecraft have in fact determined that its surface is made up mostly of water ice, with few small impurities due to organic compounds.

Credit: NASA, JPL, SSI. 

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