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Meteor showers

Several times a year the Earth drives through a trail of dust some older thing left behind. For a night or two the sky throws sparks. The best seat is a garden chair.

A meteor shower Earth driving through old dust

Naked eye only · a telescope is worse than useless here

A comet going round the Sun sheds grit all along its path. That grit stays in orbit long after the comet has gone. Every year Earth ploughs through the same trails on the same dates. So you can put them in a calendar years ahead with no working out at all.

Not every trail was left by a comet, and the two best showers in the table below were not. The Geminids come from 3200 Phaethon and the Quadrantids from 2003 EH₁, and both of those are rocks rather than dirty snowballs. Nobody is quite sure how a rock sheds a dust trail at all. It may be a comet that has run out of ice, or rock cracking in the heat every time it swings close to the Sun. The richest shower of the year is a thing we cannot fully explain.

The grains are mostly the size of a grain of sand. They hit our air at somewhere between 35 and 71 kilometres a second and burn up about a hundred kilometres above your head. Nothing lands. What you see is a bright line drawn across the sky in under a second.

A shower’s meteors all seem to fly out of one point, the radiant, and the shower is named after the constellation that point sits in — the Quadrantids after one, Quadrans Muralis, that has since been dropped from the maps. Perseids from Perseus, Geminids from Gemini. But you do not look at the radiant. Meteors near it are coming almost straight at you, so they leave short stubby trails. The long dramatic ones appear well away from it.

The ones worth staying up for, the same dates every year:

Shower	Peak night	Per hour	Worth knowing
Quadrantids	3–4 January	110	Sharp peak, only a few hours wide. Bitterly cold.
Lyrids	22–23 April	18	Modest, but the first after the winter.
Perseids	12–13 August	100	The one for children. Warm nights, school holidays.
Orionids	21–22 October	20	Grit shed by Halley’s Comet.
Leonids	17–18 November	15	Every few decades it erupts into thousands.
Geminids	13–14 December	150	The richest of all, slow and bright. Freezing.

“Per hour” assumes a perfect black sky with the radiant overhead. From a garden with streetlights, expect a quarter of that. A meteor every few minutes is still a good night. The Moon matters more than anything else. A full Moon will wash out all but the brightest.

Find my next meteor shower

Try it yourself: count them

Meteor counting is real science. People have been sending in counts for more than a century.

Lie back and face about halfway up the sky, away from the radiant and from any streetlight. Binoculars show a patch of sky far too small. Your eyes take twenty minutes to get used to the dark, and one glance at a phone undoes all of it.

Count every meteor for one full hour, and note anything odd: a colour, a trail that hangs in the air afterwards, one far brighter than the rest. Against the table above, your hour measures how dark your own sky is. Two people lying head to head, facing opposite ways, will get different numbers.