The Perseid meteor shower

Meteor showers are probably the easiest astronomical events to see, and the Perseids is one of the most spectacular. This year the shower will be in our skies from 17 July to 24 August, it will peak on 12-13 August. So how do you go about watching the show?

Perseid meteor shower

Credit: Fred Bruenjes

How to watch a meteor shower

The first thing you need to work out is where to look. The place where the meteorites originate from is called the radiant and for the Perseids this is found, as the name would suggest, in the constellation of Perseus. It’s near the ‘W’ shaped constellation of Cassiopeia if that’s a more recognisable landmark. At this time of year you can see both Perseus and Cassiopeia in north to north east of the sky, but as meteors appear over a wide area of the sky there’s no need to locate either constellation exactly. Now you’re ready to settle in for a night of meteor watching.

Perseid Sky Chart

Credit: Sky and Telescope

The great thing about meteor showers is that they are best viewed with equipment no more advanced than your eyes. You don’t even need particularly dark skies. I’ve seen them while lying down in the middle of a city (in my back garden I should add, not the middle of the road which is a terrible idea – too many street lights). All that you need is a place you can get away from direct sources of light, such as streetlamps and the moon. Luckily the Moon is a few days off new, as the light from our nearest celestial neighbour can sometimes put a dampener on things.

Once you’ve found your spot I suggest making yourself comfortable – you’re going to be there for a while. Find a place to sit down, but make sure you have some decent insulation, it can take your eyes up to half an hour to adapt and it gets cold much faster than you think. Soon enough you’ll start seeing those few flecks of light as they streak across the sky. Try and keep count of how many you see and how fast they come.

How many Perseids can I expect to see?

You may have heard a number being bandied about in the press claiming that the rate of meteors is around 100 per hour. That’s not exactly true. That number is what is called the zenithal hourly rate (ZHR). This is the number of meteors you would see if conditions were perfect, if the radiant was directly overhead at a dark sky site and if you could see the whole sky at once. Unless you are a fish (which I doubt if you are reading this) or have some very strange glasses on you cannot see the whole sky at once. For most people observing from an urban setting you’re more likely to see a third to a half of this rate. Still that will mean you’re going to see one shooting star every minute or so, which isn’t exactly shabby.

What are meteors?

So now you’ve seen a couple of shooting stars, what are they? Dust and debris from the Solar System hit our atmosphere all the time, about 100 tons every day. Most of this is dust and rocks the size of gravel that burn up * before they reach the ground without much ceremony. Some burn with a light bright enough to be seen from the ground and it’s these we see as shooting stars. However much of this is just stuff that’s floating around our planet or in its orbital path and hits our atmosphere pretty randomly.

Meteor showers a bit different in that they happen regularly. In most cases it’s caused by the Earth passing through the trail of debris left behind by a comet. In the case of the Perseids this was the comet Swift Tuttle which passes through the Earth’s orbit every 133 years, the last time in 1865. As the Earth’s orbit shifts slightly every year we haven’t managed to completely clear a path through the debris field and so we are left with the glorious sight that is the Perseids meteor shower.

So I hope that helps you some, and I hope you manage to get out there and see a few shooting stars for yourselves!

 

*: Technically the glowing isn’t caused by the meteor ‘burning’ but because it’s travelling so fast. The friction between it and the air causes the air to super heat and it’s this air that stars glowing. Of course this then melts the meteor, and there’s probably some oxidisation going on somewhere so you could say the rock is burning, but it’s not the flaming rock that you can see streaking across the sky.

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