How Close is Apophis?

About this Site

Concept and Purpose

This web site is intended to be an entertaining and informative way to keep track of one of Earth's neighbors. In addition, we hope that this site helps make people aware of the danger that asteroids and other near-Earth objects could pose. Despite all of the wonderful technology humanity possesses to map the skies, Apophis was not discovered until 2004. At the time of its discovery, it was only six months away from a pass by the Earth. Although we know now that we are not in any near-term danger from Apophis, we cannot rule out a collision within our lifetimes. If such a collision occurs, millions of people could be killed. Furthermore, hundreds of new asteroids are discovered every month. When will the next Apophis be discovered? If it is found to be on a collision course, how much time will we have to prepare? Unfortunately, we do not currently have any way to deal with this potential threat. In our opinion, preventing a disaster from near-Earth objects ought to be one of the top priorities of NASA and the other space agencies and governments in the world.

About the Author

The author of this web site, David Carson, is not an astronomer. He is a computer professional with an interest in science, and would rather not be hit by an asteroid if it can be avoided. His best-known world-wide web project is Who's Alive and Who's Dead.

Technical Background

Our data on Apophis's position is obtained from the Horizons system provided by NASA's Jet Propulsion Laboratory. We download a new set of position data as needed to take advantage of any revisions NASA may make to Apophis's orbit calculations. Our calculations are made by taking position readings from two different times - typically 24 hours apart - and interpolating the result. In other words, if NASA says that Apophis is 10,000,000 miles away at midnight on the 1st, and it will be 10,200,000 miles away at midnight on the 2nd, then we estimate that it will travel half that distance in the first twelve hours, and will therefore be 10,100,000 miles away at noon on the 1st. This is not always precisely correct, but it is accurate enough for our purposes.

NASA's data on Apophis reports the distance between it and the center of the Earth. We, however, are more interested in the distance from Apophis to the surface of the Earth, since that is where collisions would occur. Therefore, we subtract 3,951 miles - the average distance from the center of the Earth to the surface - from the distances reported by NASA.

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