Frequently Asked Questions


  • The End of the Dinosaurs, by Charles Frankel, Cambridge Univ. Press, 1999.
  • Rain of Iron and Ice, by John Lewis, Addison-Wesley, 1996.
  • Mining the Sky, by John Lewis, Addison-Wesley, 1996.
  • Comet and Asteroid Impacts on a Populated Earth, by John Lewis, Academic Press, 2000.
  • Comets, Creators and Destroyers,by David Levy, Touchstone (a division of Simon & Schuster), 1998.
  • Rogue Asteroids and Doomsday Comets, by Duncan Steele, Wiley 1995

These are more technical but very good:

  • Asteroids II, Edited by Tom Gehrels, Univ. of Arizona Press, 1989.
  • Asteroids III, Edited by W. Bottke et al., Univ. of Arizona Press, 2002.
  • Hazards Due to Comets and Asteroids,Edited by Tom Gehrels, Univ. of Arizona Press, 1994.
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There are several flavors of space object tracking software available on the internet - some free and others that cost some money. If you are looking for software that will show an object's position (RA and Dec) in the sky, there are numerous planetarium programs that do that. There are also programs that give a "space view" of the solar system from anywhere in the solar system. Here are a few sites worth checking out that may be of help:

The Minor Planet Center 
Near Earth Objects Dynamics Site 
JPL Horizons

Also, search the web for "astronomy software" for more information on programs that are available.

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Each planet in the solar system exerts some force on the Earth, however small that force may be. Most of it comes from the sun and the moon. For example, the moon is the primary reason we have tides. As you may know, twice per month there is a higher than usual tide. This occurs when the sun and the moon are lined up and acting to "tug" at the Earth in the same direction -- causing more pronounced tides. No other planets contribute to the Earth's tides because they are very far away, and gravitational force varies inversely with the square of the distance. Even if all other planets were to line up, the combined magnitude of their gravity would be insignificant compared to that of the sun and moon. It wouldn't even be detectable! So, in short, if there is a planetary conjunction in the sky, go out and watch it in comfort and with appreciation. For more "coverage", please see the popular astronomy magazines or their websites.

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We are glad to hear of your interest in our work. Please try to learn as much as you can from our publications, our web site, and the other sites to which our site links before requesting personal help. When you finally do have questions that aren't answered by our papers, it helps us if you tell us how much you already know about the subject and what you have already done to find the answers you seek. That is the most educational way to do research for school, and it helps us to write answers at your educational level.

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The images on this website have been optimized for viewing over the internet, in terms of image size and file size. Most color photographs are stored in JPEG format, allowing for true color and fast downloads. Many of the CCD images of asteroids and comets are stored in GIF format, to better represent the quality of the original. Our images of asteroids appear 'grainy' because the image displayed is only a small, magnified cropping from the original CCD image. They were magnified to make the asteroid's movement easier to see, but no pixel information was lost. So the images of asteroids on the web page are as high resolution as they can get.

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The latest news about close passes of asteroids and comets by the earth can often be found at the astronomy magazine online sites, and the NASA Solar System Exploration site, which are updated very frequently. These are often the best, most reliable, and easiest to access sources of information on fast-breaking, important, news stories in Astronomy. We can recommend:

Sky & Telescope Magazine - A popular astronomy magazine online site; current events in the sky, and news items about Astronomy. 
Astronomy Magazine - Another popular astronomy magazine online site; current events in the sky, news items about Astronomy.

NASA/JPL Impact Risk Page - NASA/JPL Impact Risk Tabulation.

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