The New Student's Reference Work/Asteroids

From Wikisource
Jump to navigation Jump to search

As′teroids, a series of small planets, sometimes called minor planets, which revolve about the sun in periods varying from three to eight years.  More than 500 of these bodies have been discovered, all having orbits lying in the space between Mars and Jupiter.  Practically all of these planets are so small they can be seen only with a telescope; though Vesta, which is the largest, can at times be seen with the naked eye.  Their diameters probably range between 10 miles and 400 miles.

In recent years many asteroids have been discovered by photography.  If any portion of the sky is photographed witn a camera attached to a telescope, the fixed stars will appear as points; but if there be an asteroid in the field of the camera, its image will be a short straight line, for it is moving among the fixed stars.

Of all known asteroids the most interesting are probably Ceres and Eros.  Ceres was the first one discovered, having been detected by Piazzi, January 1, 1801.  Eros, discovered by Witt of Berlin, August 14, 1898, proves to be our nearest neighbor and promises to offer, by observations of its parallax, the very best of all methods for determining the distance from the earth to the sun.  Since this distance is the standard of length for nearly all astronomical measurements, Witt’s discovery of this planet must be ranked among the most important astronomical discoveries of recent years.  The name asteroid is due to Sir William Herschel.