Star Gazer

Perseid meteor shower peaks on Sunday

By PAUL DERRICK

It’s time once again for the popular Perseid meteor shower, and this year we might get two nights of increased meteor activity. The shower is predicted to peak the morning of August 12, thus there could be increased meteor activity the nights of August 11/12 and 12/13.

The best viewing will likely be from dark until moonrise rise, and even after the Moon rises – around 2am August 12 and 3am August 13 – it will be in a waning crescent phase low in the east, and shouldn’t create major interference.

Meteor showers result when Earth passes through comet debris.

Meteors are best seen with naked eyes from dark skies away from light-polluted cities, but brighter meteors can be seen even from within urban areas. While in a reclined position – and reclining lawn chairs work great – slowly pan the entire sky, focusing most of your attention on the darkest part, which is usually overhead.

Meteors are tiny pieces of space debris entering our atmosphere at such high speeds – many thousands of miles per hour – that friction with air molecules causes them to burn up, creating those beautiful momentary streaks across our sky.  They resemble “falling stars” and “shooting stars” – hence their nicknames – although they have no connection with the stars we see in the night sky. Most meteors are produced by small pieces of debris no larger than a pebble, and many as tiny as a grain of sand.

Meteors are commonly seen virtually every night, especially under dark, moonless skies, but several times each year we have meteor showers during which an above-average number of meteors are seen – like the Perseid meteor shower which occurs each year around August 12.

Many ask why meteor showers occur the same time each year, and so did astronomers until about 150 years ago. Soon after the discovery of Comet Swift-Tuttle in 1862, astronomers could finally answer the question. They noticed an association between this comet and the annual Perseid meteors, and thus were able to establish that meteor showers are linked to comets.

Dubbed “dirty snowballs” by astronomer Fred Whipple, comets are chunks of frozen rock and ice, most several miles in diameter, left over from the formation of our solar system some five billion years ago. Countless millions, of even billions, of comets swarm around the Sun far beyond the orbit of Pluto in what is called the Oort Cloud, and most will remain out there throughout the life of our solar system. Some, however, have their orbits perturbed in such a way that they swing down into the inner solar system where heat from the Sun melts off part of their outer layer, freeing and distributing bits of rocky debris along their path.

By coincidence, the orbital paths of some comets intersect the orbital path of Earth as it makes its annual trip around the Sun. When this happens, Earth passes through the stream of debris left in the comet’s path, resulting in an above-average number of meteors, and thus a meteor shower.

Meteor shower names derive from the constellation from which the meteors seem to radiate – the Perseids from Perseus, the Leonids from Leo, and so forth. A key work here “seems” as the meteors don’t actually originate from within their named constellation – they only appear to. The stars forming constellation patterns are many light years away while the pieces of debris blazing across our sky are a mere 50-70 miles up in our atmosphere.

And the name doesn’t mean that meteors will only be seen in or near the constellation from which they radiate. As with all meteor showers, Perseids are likely to be seen in any part of the sky, not just in the direction of Perseus. So why are they called Perseids? If you trace their paths back far enough, the paths converge at their radiant point within the constellation for which they are named. The radiant point for the Perseids is just inside Perseus, near the Perseus-Cassiopeia border.

As you watch a Perseid meteor burn up in our atmosphere, think about the fact that you’re witnessing the demise of an ancient piece of debris that was once part of Comet Swift-Tuttle, and which had been around since the birth of our solar system.

Paul Derrick is an amateur astronomer who lives in Waco. Stargazer appears twice monthly. Paul’s website (www.stargazerpaul.com) contains an archive of past Stargazer columns, a schedule of his upcoming programs, star parties and classes, and other basic stargazing information. Contact him at paulderrickwaco@aol.com or 254-723-6346 or 918 N. 30th St., Waco, TX, 76707.