perseids

If you live in the U.S. you may have been too distracted this week by the sad news about Robin Williams and Lauren Bacall, and the terrible events unfolding in Missouri, to pay much attention to what’s happening in the sky. But there’s quite a show going on up there, and technically has been since July 24. The Perseid meteor shower is the “Old Faithful” of Northern Hemisphere skies, peaking every August 13 or 14, with as many as 60 meteors per hour shooting through the heavens. It’s kind of amazing to think about it, but the yearly Perseid show has been going on for possibly millions of years, almost certainly longer than the existence of the human species as we know it. It’s a pretty profound celestial event, but we hardly notice it.

The Perseids are so named because they emanate from the sky in the vicinity of the constellation Perseus. At least, that was the name given to them by the Belgian astronomer Adolphe Quetelet in 1835; a true Renaissance man, expert in numerous scientific fields, among Quetelet’s other accomplishments are the founding of the Royal Observatory of Belgium in 1826 and the development of the body mass index (BMI), with which you may be familiar if you eat too many cheeseburgers. Quetelet certainly did not discover the Perseids. The earliest mention of them in the historical record comes from China in about 36 CE. It seems hard to believe that for nearly 2000 years no one else noticed there was a meteor shower from the same part of the sky on the same day of every year, but Quetelet is credited with publicizing that fact.

Where do the meteors come from? We now know that the particles that fall to earth every July and August are little bits of space rock left behind in the trail of a comet called Swift-Tuttle, which orbits the Earth every 133 years. Its last appearance in Earth skies was in 1992, and it will remain invisible until 2126, but the Earth passes through the debris it leaves behind at the same time every year. Thus, unlike other comets that are very infrequent visitors, Swift-Tuttle is constantly reminding us of its presence.

There is an extremely slight possibility that Swift-Tuttle may strike the Earth, thus wiping out humanity, but that’s not likely to happen at all, and if it does it probably won’t be until after the year 4000. Until then, the Perseids will remain a yearly light-show, reliably distracting us from our Earthbound woes; tonight, in particular, we have a lot of them to forget about.

The photo of the Perseid meteors over the Very Large Telescope (VLT) array in Chile was produced by the European Southern Observatory and is used under Creative Commons 3.0 (Attribution) license.
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