This month there is a chance to witness one of the most spectacular celestial fireworks display in the night sky as the annual Perseid meteor shower reaches its peak on the night of Friday August 12th.
Most of us will have seen the occasional disaster movie featuring a giant asteroid on a collision course with Earth, threatening to wipe us all out in a catastrophic impact as the huge rock from outer space smashes into our home world. Whilst asteroid impacts have happened in the past (the last big one occurring around 65 million years ago and attributed to the demise of the dinosaurs) the Earth does get bombarded on a daily basis by debris from space, and fortunately we don’t need Bruce Willis to rescue us from it.
Meteors are small pieces of rock and dust from space, normally no bigger than the size of a grain of sand, and millions of them hit the Earth every day. They are often referred to as ‘shooting stars’ as they leave a streaky tail behind them as they flash across the sky.
When you see a meteor you are actually witnessing its destruction. The meteor would have been travelling through space at a speed of around 80,000 miles per hour and when it hits our atmosphere it heats up so much that it disintegrates in a bright flash of light. As it is still travelling at tremendous speed this light leaves a streak across the sky.
Meteors are in fact tiny fragments from comets. Comets are giant ‘dirty snowballs’, consisting of rock, dust, water ice and frozen gases such as carbon dioxide, that orbit around the Sun. As the comet approaches the Sun it will heat up and part of it will melt. This leaves a long trail of dust particles spreading out behind it for millions of miles though space. When the Earth passes through this debris trail the upper atmosphere of the planet is bombarded with a greater number of small particles than usual and we experience a meteor shower.
There are several annual showers which take place around the same time each year, such as the Leonids in November and the Geminids in December. The most visible of the annual showers is the Perseids. A meteor shower takes its name from the constellation that the meteors appear to radiate from, which in this case is the constellation of Perseus. Perseus is quite an easy constellation to find. Look east around 10pm and you will spot the distinctive ‘W’ shape of the constellation of Cassiopiea. Perseus sits below the first two stars of the ‘W’.
The source of the Perseid meteor shower is the comet Swift-Tuttle, which orbits the Sun once every 133 years. Earth enters the debris trail from the comet in mid-July and some Perseids may be seen on the nights leading up to the peak. Rates increase up to the peak on the night of the 12th, when anywhere between 60 and 120 meteors per hour are possible. The shower will start sometime between 10pm and midnight, when Perseus is well up in the eastern sky. As the night unfolds the meteor rate should increase, reaching a peak around 2am when there may be as many as one or two a minute on average. This year the Moon will set just after midnight, so interference from moonlight will be minimal.
The Perseid meteor shower is best viewed using the naked eye. Given the speed they move at and their brief duration it is next to impossible to catch a meteor in a telescope or binoculars. The best way of observing them is to wrap up very warmly, lie back on a deck chair and watch the sky. If you are planning a long night be sure to have something warm to drink and something to eat, such as chocolate, to keep the energy levels up. Try to find a dark sky site away from artificial lights as the darker the sky the more meteors you will see.
You can learn more about the wonders of the universe and see some of these amazing sights for yourself by visiting Coats Observatory on one of the winter viewing nights, which run on a Tuesday and Thursday from 6:30pm to 9pm from the end of October until the end of March. Admission is free and there is no need to book.
By John Pressly at The Coats Observatory
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