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Exploring Space
Volume 22, Number 3, Spring 1999
PHOTO: Comet Hale-Bopp
Comet Hale-Bopp. Dust, ice, gas and solid material ejected from the comet's nucleus forms a teardrop shape. Photo: NASA. [ Click for a larger image.]

The Sky Is Falling
Identifying the Cosmic Players

Try This! Make Your Own Telescope

Make your own telescope Discover how a refracting telescope works by making one from scratch , using common items. This telescope won't have a tube—that's so you can see how an image is formed inside a telescope.


RealAudio Dr. Eleanor Helin of NASA's Jet Propulsion Laboratories explains her work as Principal Investigator of the Near-Earth Asteroid Tracking (NEAT) program, which keeps a watch on bodies in space that may present a future threat to life on earth.


B y early October, backyard astronomers are picking up the approaching asteroid with their telescopes. The mile-wide chunk of space rock is on a collision course with the earth. On October 26, it's the brightest object in the sky, save for the moon. Traveling at nine miles per second, the asteroid enters the earth's atmosphere on October 28. Friction from the atmosphere heats the surface of the object to more than 3,000 degrees Fahrenheit. As the object sails through the atmosphere, it produces a streak of light that we call a meteor or "shooting star." About ninety miles above the earth, the extreme heat melts the meteor's hard shell and it bursts into a crackling, hissing fireball.

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