The annual Perseid meteor shower takes centre stage this week, painting the night sky with glowing streaks of light.
The annual Perseid meteor shower takes centre stage this week, painting the night sky with glowing streaks of light. The spectacle begins every year in mid-July and lasts through August, but the best time to take in the show this year is when the meteor shower peaks on Friday night and early Saturday.
Unfortunately, the glare of the full moon will make it hard to see some of the more modest meteors this year. The best viewing time is expected to be just before dawn on Saturday, when the moon will be low in the sky.
The Perseids appear to originate from a point within the constellation Perseus. The number of meteors visible in the sky tends to increase as the night wears on.
According to NASA, more than a dozen meteors per hour were already visible by Tuesday.
For those who don’t want to stay up until dawn, the few meteors that are visible early in the night may also be some of the most brilliant. Astronomers call these meteors earthgrazers. Long, slow and colourful, they approach from the horizon and skim along the atmosphere much to the viewer’s delight.
The show is free, so grab a seat, whether for an hour or the whole night, and if you miss the event this year you can always catch it again next August. This performance has a standing engagement.
What’s a meteor shower?
Meteor showers occur when the Earth encounters the debris fields left behind by visiting comets. As comets travel through space and near the sun, small particles of rock and metal break off, leaving fragments in their wake like a trail of crumbs.
For example, the Perseids streak through the sky when the Earth is passing through debris from Comet Swift-Tuttle. Comet crumbs called meteoroids hit the top of Earth’s atmosphere at hundreds of thousands of kilometres per hour, burning up because of friction. This may make them glow for several seconds, lighting up the night sky.
If a part of the meteor survives the trip through the atmosphere and hits the ground, it’s a meteorite. But that is a rare occurrence.
Meteoroids are usually pretty small. According to NASA, most meteors range in size from one millimetre to one centimetre in diameter, barely more than a grain of sand. The light they produce while burning up, however, is very intense and can be seen from hundreds of kilometres away.
Many people call these celestial fireworks “shooting stars,” but they really don’t have anything to do with stars at all.
Why are they so bright?
The intense light of a meteor breaking up is created when a dust particle hits air molecules in the Earth’s atmosphere. The impact vapourizes the outer layers of the meteor, leaving a trail of iron, magnesium and sodium.
When this trail of molecules makes subsequent impact with air molecules, the electrons are “bashed” out of their regular orbit with their corresponding nuclei, creating light in the process.
The colour of light produced depends upon the composition of the meteorite. Iron particles produce yellow light; sodium particles produce orange-yellow light; magnesium produces a blue-green light and silicon atoms produce red light.
How are they named?
The debris from a comet travels in parallel lines, and when that hits the Earth’s atmosphere, it appears to originate from a single point, just as parallel train tracks appear to converge to a single point.
The Perseids, for example, get their name from the constellation Perseus, because that is where the shower appears to originate. Similarly, November’s Leonids appear to come from within the constellation Leo, and December’s Geminids appear to originate from within the constellation Gemini.
Where to watch them
Find the darkest spot you can, away from light pollution. Try to get outside any settled area. In years where there is a bright moon, try to position yourself so its light is shielded from your field of vision.
Meteors can appear anywhere in the night sky and they are safe to watch with the naked eye.