2021 Perseid meteor shower

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One of the most reliable and enjoyable meteor showers in the astronomy calendar is the Perseids. Although it doesn’t necessarily have rates as high as the Geminids or Quadrantids, it’s a reliable shower and the fact that it takes place in August can make it a more pleasant experience than sitting outside in the freezing cold on a December night.

Perseid Meteor 12th August 2017 by Mary McIntyre

Figure 1: Perseid Meteor 12th August 2017 by Mary McIntyre

Meteor showers take place when Earth passes through the stream of debris left behind by a comet (or occasionally an asteroid) with comet 109P Swift-Tuttle being the parent body of the Perseids. The comet last graced our skies in 1992 and it won’t return again until 2126. The tiny particles left behind in the debris stream burn up as they enter our atmosphere and this causes a meteor, also known as a shooting star. Meteors belonging to a particular shower will appear to come from the same point in the sky and this is called the radiant. Meteor showers are named after the constellation the radiant lies in, so in the case of the Perseids, the radiant is in the constellation of Perseus.

Perseid Meteor Shower Radiant at 1am on 13th August. Graphic created by Mary McIntyre using Stellarium
Figure 2: Perseid Meteor Shower Radiant at 1am on 13th August. Graphic created by Mary McIntyre using Stellarium

The debris stream from Swift-Tuttle is quite widely dispersed so the Perseid Meteor Shower is active from 17th July until 24th August, with the peak occurring overnight on 12th / 13th August.

It’s always worth observing the nights before and after the peak as well because meteor showers can surprise us! Perseid meteors are travelling at just under 60km per second and they are characterised by green colour in their trails. This shower often produces bright fireball meteors.

The zenith hourly rate (ZHR) for the Perseids is between 60 and 100 meteors per hour, but remember this isn’t how many meteors you will see. The ZHR is an estimate of how many meteors would be visible in the whole sky if the radiant was at the zenith (the point directly overhead), assumes there is no light pollution or moonlight, and assumes you can see the entire sky. In reality the radiant is rarely that well placed, most people suffer with some kind of light pollution unless you’re in a very dark sky location, and you can’t see in all directions at once.

The reality is that from a dark location you may visually see around 30 meteors per hour at best. They won’t be evenly spread either; sometimes you can see 20 in a five minute period then nothing for 30 minutes.
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This year there will be little interference from the Moon so it has the potential to be a great year – weather permitting of course!

When you observe a meteor shower, get yourself comfortable in a sun lounger so you don’t hurt your neck. Make sure you keep warm and have a blanket handy because it can get chilly, even during the summer. Allow your eyes to become fully dark adapted so you don’t miss the faint meteors. Perseid meteors may appear anywhere in the sky, but if you position yourself so that you looking about 45 degrees away from the radiant you will get the best experience. Meteor rates always increase before dawn, because the dawn side of the Earth is facing the debris stream. With the Perseids, the radiant gets higher during the early hours of the morning so that also helps the rates to get higher before dawn.

It’s helpful to record how many meteors you see and if possible estimate their magnitudes. Remember that not all meteors you see will be Perseids; if you follow the path backwards and it doesn’t intersect the radiant, it isn’t a Perseid. If you see a bright meteor or fireball, make sure you look for the ionization trail it leaves behind.

If you do spot a fireball, make sure you report it - visit www.ukmeteornetwork.co.uk and click the “Report a Fireball” link. If you want to learn how to take photos during a meteor shower, check our Professional Tips for Meteor Photography article and You Tube video.

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