Bring a nighttime deckchair – the Perseids are here
The Perseids meteor shower is at its brightest on Tuesday night. Astrophysicist Nigel Henbest explains how they were discovered, why they are so bright, and and how best to watch them.
All eyes have turned to the sky recently, with the “supermoon” last Sunday shining 30 per cent more brilliantly than the faintest full moon of the year, writes astrophysicist Nigel Henbest. And we’re in for another sky spectacle on Tuesday: a display of celestial fireworks. Astronomers call them the Perseids, but the traditional name for these shooting stars – still used in Italy – is the Tears of St Lawrence.
On 10 August AD 258, Lawrence – a Christian deacon in Rome – fell foul of the Emperor Valerian, who decreed that all church leaders should be killed. Not for Lawrence the lions in the coliseum. Perhaps fittingly for the summer season, he was tied to an iron grille and barbecued. His last were, reportedly: “I am done on this side; turn me over and eat!”
A couple of days later – in an apparent miracle – his burning tears rained down from heaven, and they’ve reappeared every summer since. Today, we know that these shooting stars are indeed burning, though they are not teardrops but tiny fragments of rock, shed by a comet that’s traipsing around the solar system.
Ball of ice and rock
American astronomers Lewis Swift and Horace Parnell Tuttle discovered the comet in 1862. It loops around the sun in an elongated orbit that lasts 133 years and takes it further out than Neptune. Comet Swift-Tuttle last visited our neck of the solar system in 1992. This ball of ice and rock, 16 miles (26 km) across, has strewn debris all along its orbit – and the earth runs into the stream of celestial confetti in August.
Each rocky particle – about the size of an instant-coffee granule – smashes into our atmosphere at 130,000 mph (200,000 km per hour). It’s heated to incandescence, in a streak of light that we see from the ground as a meteor (shooting star). Don’t worry about one falling on your head, though: the meteors burn up completely over 40 miles above our heads.
On Tuesday night, there should be about a meteor every minute or two.
The meteors are travelling on parallel paths, but perspective makes them seem to fan out from a single point in the sky (just as parallel railway tracks seem to converge in the distance). This “radiant” lies in the constellation Perseus – a hero from Greek myth, who rescues the chained Princess Andromeda from the jaws of a ravenous sea-monster – so the display is called the Perseid meteor shower.
The Perseids are among the most reliable of the dozen meteor showers we see during the year. So we can fairly confidently predict what to expect. On the night of the maximum – Tuesday – there should be about a meteor every minute or two. If it’s cloudy, don’t worry – there’ll be quite a few meteors flashing through the sky for several days before and after.
Stay up late
But this year, we have one big enemy to contend with. It’s that supermoon! The brilliant moon is still hanging around after its starring role on Sunday. It will light up the sky so much that we won’t be able to see the fainter Perseid meteors. Fortunately, the Perseid shower always has a fair number of very bright meteors, so we should still see a brilliant shooting star every few minutes.
For the best view, get well away from streetlights. Though the meteors stream from Perseus, in the north east they can streak across the whole sky, so make sure you have a wide view of the heavens. You’ll be best in a deckchair or sun-lounger, so you can look upwards without straining your neck. Finally, even though it’s summer, dress warmly: it’s surprising how quickly you chill when you’re sitting or lying still.
For the best view, get well away from streetlights. You’ll be best in a deckchair or sun-lounger so you can look up without straining your neck.
And stay up as late as you can. After midnight, our side of the earth is turning into the meteor stream, and the action hots up considerably.
Our regular meteor display should be reliable for centuries to come. But our descendants may be in for something much more mega in late summer 4479. That year, the returning comet itself will pass very close to the earth. Instead of insubstantial dust, a massive icy rock – far larger than Mount Everest – may fall to earth. The impacting comet will explode with an energy 30 times higher than the cosmic impact that destroyed the dinosaurs 65 million years ago.
It will be time not to observe the sky, but to abandon the earth and make our home on another planet.
Nigel Henbest and Heather Couper have just published Stargazing 2014 (Philip’s, £6.99)