The orbits of the asteroids are scattered over a zone about 200,000,000
miles broad. The mean distance from the sun of the nearest asteroid,
Eros, is 135,000,000 miles, and that of the most distant, Thule,
400,000,000 miles. Wide gaps exist in the asteroidal zone where few or
no members of the group are to be found, and Prof. Daniel Kirkwood long
ago demonstrated the influence of Jupiter in producing these gaps.
Almost no asteroids, as he showed, revolve at such a distance from the
sun that their periods of revolution are exactly commensurable with that
of Jupiter. Originally there may have been many thus situated, but the
attraction of the great planet has, in the course of time, swept those
zones clean.
Many of the asteroids have very eccentric orbits, and their orbits are
curiously intermixed, varying widely among themselves, both in
ellipticity and in inclination to the common plane of the solar system.
Considered with reference to the shape and position of its orbit, the
most unique of these little worlds is Eros, which was discovered in 1898
by De Witt, at Berlin, and which, on account of its occasional near
approach to the earth, has lately been utilized in a fresh attempt to
obtain a closer approximation to the true distance of the sun from the
earth. The mean distance of Eros from the sun is 135,000,000 miles, its
greatest distance is 166,000,000 miles, and its least distance
105,000,000 miles.
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