Many people have probably noticed satellites passing overhead on a clear night and wondered what they were. Heavens-above.com maintain a set of dynamic Web pages which generate predictions of visible satellite passes for any point on the Earth's surface. To the best of my knowledge, this site is unique on the Internet because it is the only one to offer dynamically generated predictions for ANY location using the latest orbit data.
There are over a hundred objects orbiting the Earth which can be seen
with the naked eye, and this means that there will be several passing
over your location every evening, wherever you are. Due to its large
size and relatively low orbit, the Russian space station Mir is a very
bright object and can be easily seen, even under poor viewing conditions.
Satellites can be seen as star-like objects moving quite rapidly across
the sky, and most newcomers are surprised at how fast they move. They
can be distinguished from a high-flying aircraft because they normally
don't blink, make no sound, and occasionally can be seen entering or
leaving the Earth's shadow. The apparent speed is similar to a high-flying
aircraft, because Mir, for example, travels about 30 times faster but
is 40 times higher up. Satellites in higher orbits will have a slower
apparent motion which is roughly inversely proportional to their height.
Sometimes, a satellite will suddenly become much brighter for a few
seconds, when the angle between the observer, the satellite and the
sun is just right and the sunlight glints off the solar panels or some
other part of the structure. Many of the visible objects are spent rocket
upper stages which are tumbling and this causes a periodic increase
and decrease in brightness with a period of a few seconds which can
easily be observed.
My favorites are Iridium flares!