It will thus be seen that, although all the other
asteroids are situated beyond Mars, Eros, at its mean distance, is
nearer to the sun than Mars is. When in aphelion, or at its greatest
distance, Eros is outside of the orbit of Mars, but when in perihelion
it is so much inside of Mars's orbit that it comes surprisingly near the
earth.
Indeed, there are times when Eros is nearer to the earth than any other
celestial body ever gets except the moon--and, it might be added,
except meteors and, by chance, a comet, or a comet's tail. Its least
possible distance from the earth is less than 14,000,000 miles, and it
was nearly as close as that, without anybody knowing or suspecting the
fact, in 1894, four years in advance of its discovery. Yet the fact,
strange as the statement may seem, had been recorded without being
recognized. After De Witt's discovery of Eros in 1898, at a time when it
was by no means as near the earth as it had been some years before,
Prof. E.C. Pickering ascertained that it had several times imprinted its
image on the photographic plates of the Harvard Observatory, with which
pictures of the sky are systematically taken, but had remained
unnoticed, or had been taken for an ordinary star among the thousands of
star images surrounding it. From these telltale plates it was
ascertained that in 1894 it had been in perihelion very near the earth,
and had shone with the brilliance of a seventh-magnitude star.
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