What is a meteor shower?
A meteor shower is a period when many more meteors than usual are seen, all appearing to fly out from the same point in the sky, because Earth is passing through a stream of debris left by a comet or asteroid.
On any clear, dark night you might see a few random meteors, the brief streaks of light made when specks of space dust burn up high in the atmosphere. During a meteor shower that rate climbs, sometimes to dozens an hour under ideal conditions, and the meteors share a common direction. Trace their paths backwards and they seem to spring from one small patch of sky called the radiant.
Showers are named after the constellation that contains the radiant. The Perseids appear to come from Perseus, the Geminids from Gemini, and the Leonids from Leo. The radiant is a perspective effect, like the way parallel railway lines appear to meet in the distance: the meteoroids are actually travelling in parallel, and we see them converge because they are heading towards us.
Showers return at roughly the same date each year because Earth crosses the debris stream at the same point in its orbit. Dates and peak strengths vary slightly from year to year. Well-known examples include the Quadrantids in early January, the Perseids around 12–13 August, the Orionids in October and the Geminids around 13–14 December, often the richest shower of the year. Rates are usually quoted as a zenithal hourly rate, the number an observer would see under a perfectly dark sky with the radiant overhead; real counts are usually lower.
Shower meteors are almost always tiny, from sand-grain to pea size, and they burn up completely. No meteorite has been confirmed as coming from a meteor shower, so a shower is a show for the eyes rather than a chance to collect space rocks. All you need is a dark sky, warm clothing and patience; no telescope is required.