Every August the Perseid meteor shower provides a spectacular display in the night sky and in 2021, if skies are clear, we should get a decent show.
Generally, the Perseid meteor shower occurs every year between 17 July and 24 August, with the exception of the peak period 8-16 August, and a sharp peak typically seen around 11–13 August.
The peak of the 2021 Perseid meteor shower is predicted for 20:00-23:00 BST (19:00-22:00 UT) on 12 August.
For more info on the year’s displays, read our complete guide to meteor showers.
On 12 August, the 4.5-day old, 20%-lit waxing crescent Moon sets at 22:35 BST (21:35 UT), which is well before the onset of astronomical darkness for much of the country, meaning fainter Perseid meteors will be easier to spot.
Rates of Perseid activity naturally increase after local (non-daylight saving time) midnight, so the period from 01:00-03:30 BST on 13 August is optimal.
What causes the Perseid meteor shower?
Meteor showers occur when Earth passes through dust distributed around a comet’s orbit. Entering our atmosphere on parallel paths, perspective causes meteor trails to appear to emanate from the same sky location, known as the shower radiant.
Over the activity period, the radiant’s position drifts against the background stars. Peak activity represents us passing through the densest part of the stream.
For more on the science of meteor showers, read our guide What causes a meteor shower?
How to see the Perseid meteor shower
To get the best experience from the Perseids, avoid artificial light as much as possible when viewing the shower.
This doesn’t necessarily mean travelling to a dark-sky site – it could just be trying to keep nearby street and house lights out of your line of sight.
Safety is important too, so use a torch with a red filter (to preserve your night vision) to find your way. Make your own with our DIY guide on how to make a red light torch.
Let your eyes adapt to the darkness for 30-40 minutes and you’ll see much fainter meteors.
Wrap up warm with good thermals and a warm, waterproof coat.
Keep your feet warm, as the cold can really creep up through the ground even on a warm summer night if you’re standing still for long periods.
Lie back to view the stars, so that you can see a large swathe of sky without straining your neck.
A garden lounger is a great viewing platform. Look for Perseid meteors at an altitude around 60˚ in any direction.
While longest trails are seen 40–140˚ from the radiant, towards the radiant expect short trails.
A look in the opposite direction to the radiant will reveal trails that appear short and converge to a point called the anti-radiant.
Perseid displays often exhibit bright events, many of which show what appears to be an after image of the trail, which is a weakly glowing column of ionised gas.
This ‘meteor train’ fades from view as the energy in the ionised atoms is given up. High altitude winds may also affect the train, distorting its shape.
How many Perseids will we see?
If you read some of the media coverage of meteor showers like the Perseids, you might think that, at their peak, these events see a near-constant rain of bright shooting stars blazing across the sky.
Real meteor showers – while captivating and absolutely worth observing – are rarely like this.
One number that’s often mentioned is the Zenithal Hourly Rate, or ZHR. This is a theoretical number of meteors that would be visible, on average, over an hour with the radiant of the shower at the zenith and the viewing occurring under perfect sky conditions.
The ZHR isn’t a good indicator of how many meteors you can expect to see every hour, however; that figure will be lower because of things like light pollution and the typically lower radiant at the observing time.
It’s possible to roughly estimate how many Perseids you might spot, on average, near the peak of the shower.
Such a calculation suggests that while observing at around 3am (BST) on the night of the peak, a group of observers at a suburban site – where the naked-eye limiting magnitude is, say, +5 – could potentially see a rate of about 25 Perseids an hour or so.
What is a meteor?
Meteors begin their lives out in the depths of space as tiny grains of dust, known as ‘meteoroids’.
If any of these flecks of interplanetary material are unfortunate enough to hit Earth as they travel around the Sun, they collide with our atmosphere at many kilometres per second and get vaporised in the process.
The narrow ribbon of light that occurs when this happens is the meteor – what many call a ‘shooting star’ – and they’re happening all the time.
On a clear night if you look up at the stars for, say, half an hour or so, it’s highly likely that you’ll see a meteor at some point – especially from an observing site with dark skies.
Many meteors that you see like this will be what’s known as ‘sporadic’ meteors. Essentially that means that they are random in nature and can appear anywhere in the sky, going in any direction.
What’s different with the Perseid meteor shower is that Perseids, while they can materialise anywhere against the backdrop of stars, all appear to streak from a fairly-well defined point on the sky – astronomers call it the ‘radiant’.
This behaviour is, in fact, an optical illusion. The meteors are actually travelling on broadly parallel paths, as the meteoroids that create them plough into the top of Earth’s atmosphere.
It’s merely a trick of perspective that makes them look like they’re zooming across the sky from the radiant point.
While ‘normal’ sporadic meteors originate from meteoroids scattered in a fairly random way between the planets, meteors in meteor showers like the Perseids occur when Earth passes through a stream of dusty material left by a comet or asteroid as it has journeyed around the Sun.
In the case of the Perseids, that’s a cloud of dust left by Comet 109P/Swift-Tuttle.
Every year Earth’s orbit brings our planet into a position where its path intersects with that trail.We sail through the stream of dusty particles over the course of a few weeks and the result is the Perseid meteor shower.
Will we see fireballs?
The Perseids themselves can occasionally put on an impressive show of fireballs. These are brighter meteors that can light up the sky with a bright turquoise flash and are really quite thrilling to witness.
Some of the brighter ones may leave what is known as a ‘persistent train’, which is a line of superheated air and meteor ‘smoke’ that appears to glow for a few seconds, and in some cases longer, after the shooting star itself has flashed across the sky.
How to photograph the Perseid meteor shower
Photographing meteors isn’t hard, but the tricky bit is having your camera pointing in the correct direction with the shutter open as a bright trail appears. Being able to optimise the probability of this happening is the key skill in meteor photography.
A manual camera works best for meteors: something like a DSLR or a mirrorless or a bridge camera. A wide lens works best but there are limitations to weigh up.
Your chances of capturing a trail increase with sky coverage, so a fisheye lens covering the entire sky might sound like a good bet, but unfortunately most trails will be puny and difficult to see.
As you increase focal length the field of view narrows, reducing the probability of capturing a trail because some will occur outside the frame area.
But, if you are lucky and capture a trail using a longer focal length lens, it will invariably have more presence than a fisheye would deliver.
The balance between area covered and meteor trail appearance is reached around the 14–20mm mark, although this isn’t written in stone.
A fast lens is also preferable to a slow one. Setting the lens fully open allows the maximum light in, but can also introduce distortions in star shapes towards the edge of field.
A common mistake for those more used to deep-sky astrophotography attempting meteor trails is to set the sensitivity high, look at a test result on the back of the camera and reject the ISO setting because the image quality looks poor.
This is because deep-sky images benefit from mid to low ISO values to maintain tonal quality and keep noise to a manageable level.
But meteor trails don’t last long, typically less than a second, and to capture them the deep-sky imaging philosophy needs to be put on hold and the camera ISO ramped up for high sensitivity.
Meteor photography is like celestial fishing, you never know what you’re going to catch!
- Recommended equipment: DSLR or mirrorless camera with a lens of focal length 14–20mm
Photographing a Perseid meteor: step-by-step
Choose your lens: a 14-20mm focal length is ideal, and the fastest possible is recommended. Lens speed is measured by the lowest value the focal ratio (f-number) can be set to. An f/2 setting will do better under low light than one of f/3.5. You could have one camera for wide-fields, and one at a longer focal length for narrower views.
You don’t necessarily need a tracking mount for meteor imaging. A sturdy tripod will be adequate. If you do choose a tracking mount, make sure it’s not going to rotate the camera into a position where part of the sky is obscured later on. Aim the camera at an altitude 60° above the horizon, with the centreline of the long frame axis pointing back towards the shower radiant.
Set the camera to manual or bulb, and the lens to manual focus. Adjust the f/number to its lowest, but close by a stop of two if the stars are distorted. Set a mid- to high-ISO and choose an exposure length; try 30” to begin. You can work the camera automatically with continuous shooting and a lockable remote shutter release.
Have plenty of spare charged batteries to hand for your camera, or obtain a mains adaptor. Dew is also a problem on meteor watches; various heater band solutions are available, or an online search will reveal ways to make your own. Carry out regular lens checks, armed with a 12V hairdryer to clear any moisture.
Pre-focus the lens at infinity; using the Live View function on a bright object such as Jupiter is one way to achieve this. Jupiter’s Galilean moons make good focus targets. Take a test shot and examine it. If it’s too dark, consider upping the ISO setting. If too bright, lower the ISO or shorten the exposure, but not below 10”.
This part of the process requires patience. Set the camera going, sit back and enjoy the visual view. Next, download the images and go through them looking for meteor trails. A program such as Faststone View is good for this. If you find a trail, rename it by adding a ‘meteor_’ prefix to the name.
Pictures of Perseid meteors
If you’re in need of some inspiration, below is a selection of Perseid meteors captured by astrophotographers and BBC Sky at Night Magazine readers.
Pete Lawrence is an experienced astronomer and a co-presenter of The Sky at Night. This guide originally appeared in the August 2021 issue of BBC Sky at Night Magazine.