Perseid perfection
The peak of this year’s Perseid meteor shower promises to be a fine sight under dark skies. Will Gater gets you ready for the show
Get ready for this year’s unmissable meteor shower!
Summertime astronomy in the UK can be something of a blearyeyed marathon, with late-night observing sessions to grasp anything that seems like darkness amid the glow of twilight. Every August, though, we get our reward for persevering through these months in the form of the Perseid meteor shower and this year – if the skies are clear – we should get a decent show.
On the night of the shower’s peak, on 12 August, the Moon sets at around 22:30 BST (21:30 UT), which is well before the onset of astronomical darkness for much of the country; with no moonlight to wash out the sky, fainter meteors will be easier to spot. But what causes this wonderful celestial spectacle and what do you need to do to make the most of it? That’s what we’re going to tackle over the following pages.
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 this month 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’.
A trick of perspective
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