David McLarty, age 13, of Douglasville, Georgia, for his question:

How often do we see a supernova?

A supernova is one of the most dramatic events that can occur within a galaxy of stars. It is thought to be a mammoth nuclear explosion that turns a total star to cosmic dust. If a star situated at a distance from us of 40 light years became a supernova, its blazing glory would lobk'Y4 times brighter than our full moon. Its actual luminosity could be 200 million times more brilliant than the sun. Supernovae have been observed in our Galaxy only three times in recorded history. One occurred in 1054, another in 1572 and the most recent one in 1604, Astronomers estimate that any galaxy can expect a supernova on an average of once in 400 years.

We have not seen a supernova in our Galaxy for three and a half centuries and we have no way to predict the appearance of the next one. It may burst forth with a blaze of glory next week,...next year or wait for several hundred years. Astronomers, however, often get a chance to observe these cosmic spectacles. Once in a while they appear on telescopic plates of other star studded galaxies far beyond our Milky Way.