A common slang term for a large apertures . Both the light and the loss of contrast make it difficult to find fainter stars and nebulae. This is becoming a bigger problem for both amateur and professional astronomers. The rocky solid ball of a planet or a satellite. A region in which the electromagnetic force makes itself felt.
Astronomers use magnitudes to describe the brightness of an object in the sky.
It is a non-linear, numerical scale where the smaller numbers represent brighter objects. Generally, the unaided eye can see stars down to magnitude 6 in good skies. Pluto is magnitude 14, and thus, is invisible without optical aid or photography. A diameter passing through the foci and center of an ellipse. See catadioptric .