Driving a lonely highway through West Texas in early November, Richard and I watched the sun set over the jagged spines of distant mountain ranges. As darkness crept across the landscape, the fiery after-glow faded, leaving a luminous band of gold along the western horizon.
Suddenly, a ball of blue-white fire streaked across the sky above the highway, passing right through the after-sunset glow. A sparkling orange and blue tail trailed the speeding star and hung glittering in the heavens for a few heartbeats after the meteor burned out.
“Wow!” said Richard. “I think that’s the most spectacular meteor I’ve ever seen.”
That falling star was a precursor to this year’s Leonid meteor shower. Although the height of the shower is November 17th and 18th, when as many as 100 meteors an hour may be visible, the “rain” of meteors began several weeks ago.
Named for the constellation of Leo, the area of the heavens where the falling stars appear to originate, the Leonid meteor shower is triggered when Earth passes through the stream of dust, ice, and rock chunks shed by Comet Tempel-Tuttle on its orbit around the sun. This particular shower is known for the unusual colors of the meteors and their persistent tails.
Meteors are born when bits of comet-debris, most the size of dust-grains, slam into Earth’s oxygen-rich atmosphere and these particles ignite. Drawn by the pull of our planet’s gravity, the burning space-litter streaks earthward, tracing a line of light across the sky.
The flare of a falling star is simply energy discharge: as the meteoroid collides with air molecules, its outer layers are abraded into a vaporous shell. Continuing collisions “excite” the electrons in this gassy aura around the streaking particle, knocking them into higher-energy orbits; when the electrons return to their normal state, the released energy is visible as light.
Very visible: meteoroids as small as one millimeter across (four-hundredths of an inch) can create a flash visible more than a hundred miles away.
The color of the light is determined by the meteoroid’s mineral composition. Sodium atoms give off orange-yellow light, iron atoms create yellow, magnesium flares blue-green, calcium adds a violet hue; silicon atoms and molecules of atmospheric nitrogen produce red light.
Those extraordinary hues, plus the persistent trails that about 10 percent of Leonid meteors write like streaks of sparkling chalk on the dark heavens, are what make the Leonid shower worth getting up for.
(The best times for meteor-watching are between midnight and dawn, when our side of the Earth is headed into the trails of comet-debris.)
So on the 17th and 18th, Richard and I will rise in the wee hours to watch for the miracle that occurs when Earth’s gravity sucks particles of comet dirt into our atmosphere, creating the evanescent streaks of light called falling stars.
Perhaps we’ll see one as spectacular as the falling star that streaked through the sunset after-glow that night in West Texas.
Copyright 2009 Susan J. Tweit
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