This regular display of “shooting stars” from the Perseid meteor shower peaks in the second week of August. Observing conditions are ideal in 2021, as the Moon’s phase will be a waxing crescent on the night of maximum and will set by late evening, allowing the rest of the night to watch for Perseids in a dark sky.
The build-up to this peak is quite gradual, with the first Perseids being visible in July, and meteors still being seen in late August. The best nights to watch for Perseids in 2021 will be in the run-up to maximum. In the days afterwards, moonlight will begin to interfere more, later into the night.
Traditional guides give dates around July 17 as the start of the Perseid meteor shower, so you may already have seen some. Rates in the early days are a lot lower than the 100 or so an hour predicted at maximum on the night of August 11/12. The shower then tails off, and August 24 is quoted as the date for the shower’s end.
Related: How to observe meteors
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However, recent research has discovered that Perseid meteors can actually be seen for a lot longer. Cameras regularly monitoring the sky have detected some outlying meteors from the shower as early as July 1 and as late as September 3, according to NASA meteor expert Peter Jenniskens.
For the highest rates, you do usually need to look on the nights close to the peak.
The shower is named after the constellation of Perseus because, when their paths are traced backwards, Perseid meteors all appear to diverge from a point, called the radiant, within it.
But the radiant itself moves against the sky during the period of activity. And at the extreme dates when meteors have been seen, it lies in two neighbouring constellations. On July 1, the radiant lies in the famous W-shaped constellation of Cassiopeia, and at the start of September it has moved into Camelopardalis.
Here is a cool, interactive visualisation of how the Earth interacts with the Perseid meteor stream every year. The meteors are produced from a dust cloud left by Comet 109P/Swift-Tuttle which has an extended orbit carrying the particles deep into the Solar System.
The theoretical figure quoted for the number of meteors seen is the Zenithal Hourly Rate (ZHR). This is calculated for ideal conditions, including a dark, moonless sky and with the shower’s radiant in the zenith, or overhead.
You do not need a telescope to view meteors. Find a sunlounger or comfortable deckchair, get away from streetlights and then spend some time simply looking up at the sky. If the Moon is in the sky, try watching the sky in the opposite direction, if possible.
You will hopefully see your first meteor within a few minutes. They appear at random, rather than equally spaced intervals, so don’t be surprised if you then see a couple within a few seconds before waiting a few minutes for the next!
You may occasionally see a starlike point moving more slowly against the heavens. It is likely to be one of the many satellites that now orbit the Earth. They can be distinguished from aircraft because they are silent and tend to show a single steady white glow whereas planes have coloured flashing lights.
Related: All you need to know about the Perseid meteor shower
Two other showers are active in July and into August. One is the Delta Aquariids, which reach a peak on the night of July 28/29. The radiant is low from mid-northern latitudes, so peak rates are unlikely to exceed 10 to 15 meteors an hour under ideal conditions.
You may also see meteors from the Alpha (α) Capricornids stream, which peaks on the same night. This is a weak shower but can produce bright, slow-moving “shooting stars”.
In 2021, bright moonlight from a waning gibbous Moon will make observation of both these showers difficult around maximum, though the α Capricornids are rich in fireballs.
Meteor astronomer Dr Jenniskens works with the SETI Institute and NASA Ames Research Center, and his discovery of the extended displays was made thanks to the NASA-sponsored project Cameras for Allsky Meteor Surveillance (CAMS) in Northern California.
Good luck in watching the 2021 Perseids!
Related: See photos of Perseids from 2018
Related: What’s in the sky this month
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