The planet that varies most in the beauty of its aspect is Mars. It is
as much as fifty times brighter when it is nearest to us than it is at
its greatest distance from us. At its brightest it is many times more
brilliant than any of the first-magnitude stars; but when it leaves our
neighborhood and goes far off into space in its journey around the sun,
its glory is so dimmed that it becomes not brighter than an ordinary
second-magnitude star, such as the pole-star, and less brilliant than
the brightest stars in the Big Dipper.
These extreme changes of brightness are due not so much to any great
distance that Mars goes from us in comparison with other planets as
to its coming so very near to us at times. It is, after all, a small
body, and no great distance, as heavenly distances go, is required to
make it show so. But the eccentricity of its orbit brings it sometimes
very near us, and its near approaches are at a time when we can see
its entire disc, and not a mere crescent, such as we see when Venus
is nearest to us. Mars does not come quite so near to us as Venus
comes, but when he is in the best position to be seen he is much nearer
than she is when in her best position. For we have seen that Venus is
brightest before she reaches her nearest position to us, while Mars is
brightest when he is at his nearest to us. When Venus is at greatest
elongation she is three times farther away than Mars is at his nearest.