TCS Daily


Star Power: The Leonid Shower and the Origins of the Universe

By Sallie Baliunas - November 19, 2001 12:00 AM

Editor`s note: The Leonid meteor shower thrills scientists and stargazers when it occurs every 33 years. TechCentralStation.com`s Dr. Sallie Baliunas watched and studied this year`s shower and filed these informal remarks. Her comments offer us a chance to understand the joys - intellectual, aesthetic, personal - to be found through scientific inquiry and discovery.

I rise before dawn has swept the stars from the sky, and I watch these stars.

This morning the familiar mighty hunter Orion -- his sword sheathed but club and shield ready, followed by his loyal dogs, Canis Major and Canis Minor -- ran triumphantly through the black vault of the moonless heavens.

But the stars felt different today. As always, they glinted and gleamed, but this morning they paled to the space woven between them. Evanescent silent streaks lit the inky background tapestry with exuberance incomparable even to rocket exhaust, the most extravagant sky light Homo sapiens has created.

The Leonid meteor shower had burst the darkness of space. Shooting, or falling, stars exploded soundless flares, some faint and brief, some leaving ion trails persisting for seconds while they traveled from the zenith to be lost over the horizon. A few reflected bright glimmers off my brass flagpole. In an hour in suburban New England I saw over three hundred shooting stars, or one every few seconds on average. But the average does not tell the story. Sometimes there were five at once, and a glance could not be sure that some were missed in another direction. Because the insistent light of suburbia robs some darkness, I missed many fainter firestreaks.

Early reports figure this Leonid display is an actual meteor storm rather than a shower. A storm reaches beyond a threshold of 1,000 shooting stars per hour, and this year the Leonids may have yielded 1,500 per hour at its peak over America.

If traced backward on the sky the fiery trails converge on a point in the constellation Leo, an important clue to their origin. The Leonids start as dust debris evaporated from returning comet 55P/Tempel-Tuttle during its close approach to the sun every 33 years. The long, trailing dust clouds accumulate in the tail of the comet. During November every 33 years or so for several years following the comet`s passage near the earth`s orbit, the earth sweeps near the clouds. This year the earth threads near the clouds emitted in 1699, 1766, 1799 and 1866.

The clouds of Tempel-Tuttle are gossamer marvels. Dust particles, most no bigger than a pinpoint, whisk through the earth`s upper atmosphere, compressing and energizing the air while the small motes disintegrate. A pale greenish-white glow marks the disintegration of comet debris.

Although tiny, the dust smashing into earth`s air molecules travels at velocities over 155,000 miles per hour. At such speeds the particles carry considerable momentum that could damage sensitive components of artificial satellites, like solar panels. The space faring societies of the world yesterday rolled, pitched and yawed their satellites to best protect sensitive surfaces.

The Leonid storm this morning was the most spectacular I`ve seen. But it is dwarfed by earlier storms over America, e.g., the night of November 12-13, 1833. At peak the storm drove over 100,000 shooting stars per hour. While shooting stars were known as a natural feature of the night sky, little was known about the cause of them, thus the Leonid storm could not have been predicted. Observers were startled by the storm`s intensity. Neighbors were quickly wakened to watch the display, which lasted for several hours. Some of the individual ion trails glowed for minutes.

The remarkable Leonid storm of 1833 first sparked quantitative understanding of meteor storms and showers generally. Thus began the quest for science to unravel yet another of nature`s splendors.

Also strong was the fierce 1966 Leonid storm with perhaps as many as 150,000 shooting stars per hour at peak intensity. And as intense as this year`s storm was over America -- if you missed it, you have another chance next November. Scientists at Australian National University and Armagh Observatory estimate a peak of 10,000 meteor streaks per hour on November 19, 2002 over America - roughly ten times the peak rate this year over America. I`ll be watching from the spectacular skies of Mount Wilson Observatory near Los Angeles, despite the moonlight that was absent this year.

Shooting stars remind us that space contains perils. But more fantastically, the stars that fall to earth tell of the origin of the earth, built over eons from just such dust clumping and amassing 4.5 billion years ago. Such comet stuff contains a significant fraction of extraterrestrial organic matter that continues to land on our doorstep.
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