Perseids bring fiery show to August sky
The Perseids are coming the most famous, predictable, and visible meteor shower in the Northern Hemisphere.Skip to next paragraph
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August is the time of year when astronomers and the rest of us bond. No telescopes, not even binoculars, are needed just a comfortable dark spot flat on your back, be it hammock, lounge chair, or blanket, looking slightly northeast and toward the zenith after 10 p.m. on Aug. 11.
If you're fortunate enough to be by a lake, take a rowboat out, pull in the oars, and lean back.
Memories easily connect warm summer nights and the Perseids. For children, it's often the first time that looking up at the stars means something exciting will happen. Not just a chance glimpse at a "shooting star," but the awe of watching meteor after meteor streak across the sky.
The "shooting stars" or meteors we see throughout the year are a tiny fraction of the myriad streams of comet dust in space. Our best two meteor showers each year are the Perseids and the Geminids (in December, peaking around the 14th), each named after the constellations from which they appear to come.
Of course, "shooting stars" is just an expression. Stars are astronomically large, often many times the size of our sun, and too incomprehensively far away to "shoot" across our relatively puny skies. This is a good thing. Were even the smallest star to come barreling toward Earth, well, let's not think about it.
The Perseids are the size of a grain of sand zooming along at 132,000 m.p.h. They are visible for only a second or two but their incandescent images linger in memory much longer. Predictions this year are that the shower will peak at upward of 60 meteors an hour at 2 a.m. on Aug. 12 and again on the 13th.
The first arrivals start in dribs and drabs about a week before the 12th, and continue, petering out, for about a week.
They are galactic residue of comet Swift-Tuttle which every 130 years sweeps in from deep space beyond the planet Pluto. The comet hurtles through the plane of our solar system not far (but far enough not to pose a threat) from Earth's orbit.
The first reported sighting of the Perseids was in the Chinese annals in 36 AD when "more than 100 meteors flew thither in the morning."
How does the shower happen?
Comets are giant snowballs with stellar dust frozen inside. The comet's ice traps the dust. But as a comet travels close to our sun, the ice particles heat up. They become gases (just think of dry ice) pulled along in the comet's tail.
As the ice is transformed into gas, dust particles in the ice escape and float free. The particles continue to orbit in the gravitational field of the comet, following it like the wake from a ship spreading farther and farther from the comet. The result is a band of tiny particles traversing the sun in an enormous elliptical ring.
And every year, as the Earth crosses this ring, the dust particles burn up, incandesce, when they collide with the atmosphere, causing the phenomenon we marvel at a meteor shower.
The point of impact between the earth's orbit and the meteors' orbit is called the radiant. The Perseids' radiant, occurs close to the constellation Perseus (hence their name), just below the constellation Cassiopeia, the ancient queen fated to remain seated on her throne for eternity. You can easily identify her as a large W on its side.
The impact takes place some 80 miles above Earth's surface. And before the dust particles are five times the height of our highest-flying commercial aircraft, they "flame out."
Since they are only dust particles, this also means they will not cause the life-ending impacts Hollywood has made so much of lately.