Glossary



Albedo
Albedo refers to an object's measure of reflectivity, or intrinsic brightness. Albedo is calculated as:
Amount of reflected radiation / total amount of radiation wich fell on the object
So a white, perfectly reflecting surface has an albedo of 1.0; a black, perfectly absorbing surface has an albedo of 0.0.

Occultation
The covering up of one astronomical object by another. For example, the Moon occults many stars each night.

Resonance
The selective response of any oscillating system to an external stimulus of the same frequence as the natural frequency of the system. Under such conditions the nodes of the two wave trains coincide, and the waves of the initial system increase in amplitude. The natural mode of oscillation of a star varies inversely as the square root of its mean density; if the sun were to start resonating at its natural frequency, it would have a period of about an hour.

Retrograde
In a backwards direction; in astronomy this means in a direction corresponding to east-to-west.