Albedo
Written by Tega Jessa
Albedo is a measure of an object's reflection of the Sun's radiation. This term is important in Astronomy as many planetary bodies in the Solar System are visible due to the reflection of the sun's light off their respective surfaces. This is why we can see planets like Venus, Mars, and Jupiter.
The measurement of albedo is a subjective scale ranging from 0 for complete dark to 1 for completely bright. For example, snow has an Albedo of 0.9 and coal has an Albedo of 0.1. The Earth has varying Albedo scores. Dark soil has one of the lowest Albedo scores with .05 or 5%. The brightest are snow, deserts, and clouds with albedo scores at .09 or higher. On average the Earth's Albedo is around 30%. Some objects have lower albedo scores than expected. The moon for example has a surprisingly low Albedo of only 0.12.
There are two main kinds of albedo. One is black sky albedo and the other is white sky albedo. Black-sky albedo is the reflection of a surface under direct illumination. The white-sky albedo is reflection of a surface under diffuse or indirect light. Albedo is also important in Astronomy as it can give astronomers additional information about objects in the Solar System such as planets and other rocky objects. In the same way that spectroscopy analyzes wavelengths of light to find out the composition of a star, albedo can hint at the surface of a planet or other body because of changes in brightness. This even has an impact on the current discussion of the Earth's climate change
Another interesting fact about the albedos of objects in the Solar System is that the farther away from the Sun you get, the lower the albedo score. This is because the intensity of the Sun's radiation drops off over greater distances.
Albedo can also be used to detect if an celestial object in the Solar System is likely to have organic compounds. This probably because many organic compounds are carbon based and on the Albedo scale has one of the closest scores of 0.
To return to the more local effects of Albedo the reflection of the Sun's rays can change climates. It is commonly understood that cooling of the Earth is in part caused by the Sun's rays being reflected rather than absorbed. That is why there is concern about the polar ice caps melting since this would reduce the Earth's general albedo meaning more heat absorbed from the Sun which could accelerate global warming.
If you enjoyed there are other astronomical articles you might like. There is a great article about the Moon's Albedo. There is also an article that is more detailed about the Earth's Albedo.
There are also great resources on the web. There is a Georgia State University site which has a pretty concise explanation about Albedo and some comparison measurements to the Albedo of other objects in the Solar System. The National Snow and Ice Center site has an article that talks about the important role albedo has in regulating the Earth's temperature.
You might also like to listen to an episode of Astronomy Cast. Episode 50 Venus is one that might interest you.
Filed under: Astronomy
