Magnitude, stellar:
A scale for expressing the brightness of a celestial object. Each unit change
of a magnitude implies a change of 2.512 times in brightness. Thus 5
magnitudes correspond to a brightness ratio of 100 times, 10 magnitudes to
10,000 times, and so on. A star barely visible to the naked eye on a clear,
moonless night is approximately of 6th magnitude. The
brightest stars are of 1st, zero, or
even negative magnitude.
Meridian, celestial:
The great circle passing through the north and the south points of the horizon
and the observer's zenith.
Meteor:
A body of rock or metal that on entering the earth's atmosphere is heated to
incandescence by friction. More about meteors can be found in the
glossary for comets and meteors by Gary
Kronk.
Meteor Shower:
A display of meteors related to one another by motion in parallel path. A list
of meteor showers can be found in the
meteor shower calendar sorted for each month of the year (by G. Kronk).
A very brief overview is available, too.
Meteorit:
Surviving portion of a meteor after traversing the earth's atmosphere and
striking the earth.