Meteor showers

Every year the Earth passes through the same streams of comet and asteroid dust at the same points of its orbit, and the sky shows each crossing as a shower. Here is where the major showers fall, when each one peaks this year, and how much of the Moon is lit at the time.

This year

The Earth’s orbit as a circle of solar longitude, 0° at the March equinox on the left and running anticlockwise, with the months round the rim. Each arc is a shower’s active stretch and the line across it the peak; the small disc on the orbit is the Moon at that peak. The gold dot is where the Earth is today.

The peaks in order

Times are on this device’s clock. The moonlight is how much of the Moon is lit at the peak, whether or not it is above the horizon where you are.

The showers, by the IMO’s figures

Shower	Active	Peak, solar longitude	Peak rate (ZHR)	Radiant
Quadrantids	28 December to 12 January	283.15°	110	Boötes
Lyrids	14 to 30 April	32.32°	18	Lyra
Eta Aquariids	19 April to 28 May	45.5°	50	Aquarius
Southern Delta Aquariids	12 July to 23 August	127°	25	Aquarius
Perseids	17 July to 24 August	140.0°	100	Perseus
Draconids	6 to 10 October	195.4°	variable	Draco
Orionids	2 October to 7 November	208°	20	Orion
Leonids	6 to 30 November	235.27°	15	Leo
Geminids	4 to 20 December	262.2°	150	Gemini
Ursids	17 to 26 December	270.7°	10	Ursa Minor

Solar longitudes are for the equinox of J2000.0, as the International Meteor Organization gives them. ZHR is the hourly rate one observer would see under a perfectly dark sky with the radiant overhead.

What a shower is

A meteor is a speck of dust, most no bigger than a grain of sand, burning up high in the atmosphere at tens of kilometres a second. A shower happens when the Earth crosses the trail of debris left along a comet’s orbit, or in a few cases an asteroid’s: the Perseids come from comet Swift–Tuttle, the Leonids from Tempel–Tuttle, the Orionids and Eta Aquariids both from Halley’s Comet, and the Geminids from the asteroid Phaethon. The trail stays where it is while the Earth goes round, so a shower returns at the same point of the orbit every year, which is why its peak is given as the Sun’s longitude rather than a date. Its meteors all seem to come from one spot in the sky, the radiant, which gives the shower its name.

How the dates are worked out

The page takes each peak longitude from the IMO’s list, adds the precession since 2000, 50.29 seconds of arc a year, to bring it into the frame of the year shown, and finds the minute the Sun reaches it with the same astronomy as the rest of the site. The Moon’s phase is worked out for that minute. A real peak can come hours early or late, some showers have broad maxima that last a day or more, and the Draconids are usually weak but have produced storms. The rates are what an ideal sky would show; real counts are lower, and a bright Moon hides the fainter meteors, which are most of them.

What it claims

Meteor showers are astronomy, not astrology: dust meeting air at a known point in the Earth’s orbit. The page says when each peak falls and how much moonlight there is, and it describes the sky and nothing more.

Questions people ask

When is the best time to see the Perseids?

Find the Perseids in the list of peaks for the year you want: the line gives the minute of the peak on this device’s clock and the share of the Moon’s face lit at that moment. The shower is best seen from the northern hemisphere, from a dark site, and usually after midnight, when the radiant in Perseus stands higher. If the moonlight note says a bright Moon, the fainter meteors are washed out, so watch while the Moon is below the horizon. The shower lasts for weeks, so nights either side of the peak also show meteors.

What does ZHR mean for a meteor shower?

ZHR, the zenithal hourly rate, is the number of meteors one observer would count in an hour under an ideal sky: completely dark, with the radiant straight overhead. It is a standard for comparing showers rather than a count to expect. Real rates are lower, often much lower, because the radiant is rarely overhead, towns and moonlight brighten the sky and most meteors are faint. In the table on this page the Geminids and the Quadrantids have the highest figures, and the Draconids have none, because their rate varies so much.

Where do meteor showers come from?

From dust left by comets and, in a few cases, asteroids. As a comet passes the Sun it sheds grains that spread out along its orbit, and every year the Earth crosses that stream at the same point, so the shower comes back at about the same time. The grains hit the upper atmosphere at tens of kilometres a second and burn up as streaks of light. Their paths run parallel, so by perspective they seem to spread from one point in the sky, the radiant, which gives the shower its name.

Why do meteor shower dates change slightly each year?

A shower peaks when the Earth reaches a particular point in its orbit, measured as the Sun’s longitude, and the calendar does not keep exact step with the orbit: the year is about a quarter of a day longer than 365 days, which leap years correct only in whole-day steps. That moves each peak by some hours from one year to the next. This page takes the IMO’s peak longitudes, allows for precession and finds the minute for the year you choose, though a real maximum can still come a few hours early or late.