One of the best annual meteor showers of the year is lighting up the night sky this week. It's the old reliable Perseid meteor shower that peaks Wednesday night and early Thursday morning, although the meteor viewing should be pretty good most of the week.
Last year, the Perseids were lousy because at the same time there was a full moon whitewashing sky and obscuring all but the brighter meteors. This year, it's a whole new ball game. Skies will be a whole lot darker with just a thin crescent moon rising after midnight. Even if you're stuck watching the Perseids in the urban and suburban lit up skies, you should see a decent number of meteors or "shooting stars."
You'll greatly add to your Perseid pleasure if you can travel out to the countryside, if you're not already lucky enough to reside there. Maybe even plan a camping adventure. In the backdrop of the dark starry heavens, you may see more than 60 meteors an hour. However, if you're with someone, maybe that special someone, and better yet your family and friends, you may collectively see even more, maybe more than 100. Just lie back on the ground or a reclining lawn chair, have some light blankets and a light jacket, and of course, be ready with repellant for mosquitoes.
Meteor showers occur when the earth, in its orbit around the sun, plows into a debris trail of dust and pebbles left behind by a comet that's passed by. The "parent" comet for the Perseids is Comet Swift Tuttle, which was last around this part of the solar system in the early 1990s.
The best way to describe a comet is to compare it with a dirty snowball. As comets get close to our sun, some of the very icy nucleus of the comet melts and frees very small particle dust and pebbles in its wake. These billions of meteoroids, as they're more formally known, all become potential ammunition for meteor showers. It's a sparse debris clouds though as the individual meteoroids are more than 60 miles apart from each other average.
By the way, Swift Tuttle is big comet with a 16-mile wide nucleus, way bigger than the comet that struck the Earth around 65 million years ago, wiping out the dinosaurs. Fortunately, Swift Tuttle isn't expected to come anywhere near Earth in the far future, although if your retirement funds hold out long enough, it will pass within 30 million miles of Earth. You may feel a swish.
Meteors in any meteor shower are best seen after midnight and that's because of the Earth's rotation. After midnight, you're on the side of the Earth that's rotated into the direction of the comet debris. In fact, you've really got a "front seat view" shortly before the start of morning twilight. As Earth rips in the comet trail at around 6,5000 mph the meteors slam into Earth's atmosphere at speeds anywhere from 30 to more than 40 miles per second. Air friction incinerates the dust size to pebble size debris at altitudes about 60 miles high, but the streaks of light you see is not due to incineration. There's no way you'd be able to see their demise as tiny as they are so far up in the sky.
Most of the light to see from meteors is caused by ionization. Even though most of the meteoroids are tiny, they temporarily but greatly excite the atoms and molecules in the column of air causing an extremely vivid collective glow. Often times, even after you see the initial streak, there's a luminous trail that can go on for a few seconds. That's the column of air getting its molecules and atoms back together in their original stable state. Meteors can also have some color to them: blues, greens, reds, yellows and more depending on the nature of the material, the speed and angle they're coming in at and the height at which they become visible.
Different meteor showers are referred to by the constellation where their radiant is. The radiant is the point in the general direction in the sky that the meteors seem to be coming from. In the case of the Perseids, the radiant is the constellation Perseus. This time of year the constellation Perseus resides in the east northeastern sky in the post midnight hours. That doesn't mean that the meteors will be restricted to that part of the sky, however. They will be literally all over the sky, but their tails will seem to point back in the general direction of the constellation Perseus.
In fact, it's not even necessary to be able to find and identify Perseus in the sky. Again, my advice is just to lie back on the ground or on that reclining lawn chair and roll your eyes all around the sky, maybe slightly favoring the eastern sky.
If you own a DSLR camera, you can get some extremely cool photos of the meteor showers. The best guide I've seen come from the American Meteor Society. Check out more at http://www.amsmeteors.org/ams-programs/how-to-photograph-meteors-with-a-dslr/
Don't you miss the Perseids. It's one of best sky shows of the summer.
(Lynch is an amateur astronomer and author of the book, "Stars, a Month by Month Tour of the Constellations." Contact him at mikewlynch@comcast.net.)