The distances and magnitudes of the Stars are as astonishing as their
numbers, Sirius, for instance, being about twenty times as heavy as the
Sun itself, 50 times as bright, and no less than 1,000,000 times as far
away; while, though like other stars it seems to us stationary, it is in
reality sweeping through the heavens at the rate of 1000 miles a minute;
Maia, Electra, and Alcyone, three of the Pleiades, are considered to be
respectively 400, 480, and 1000 times as brilliant as the Sun, Canopus
2500 times, and Arcturus, incredible as it may seem, even 8000 times, so
that, in fact, the Sun is by no means one of the largest Stars. Even the
minute Stars not separately visible to the naked eye, and the millions
which make up the Milky Way, are considered to be on an average fully
equal to the Sun in lustre.

Arcturus is, so far as we know at present, the swiftest, brightest, and
largest of all. Its speed is over 300 miles a second, it is said to be
8000 times as bright as the Sun, and 80 times as large, while its
distance is so great that its light takes 200 years in reaching us.

The distances of the heavenly bodies are ascertained by what is known as
"parallax." Suppose the ellipse (Fig. 54), marked Jan., Apr., July,
Oct., represents the course of the Earth round the Sun, and that A B are
two stars. If in January we look at the star A, we see it projected
against the front of the sky marked 1. Three months later it would
appear to be at 2, and thus as we move round our orbit the star itself
appears to move in the ellipse 1, 2, 3, 4. The more distant star B also
appears to move in a similar, but smaller, ellipse; the difference
arising from the greater distance. The size of the ellipse is inversely
proportional to the distance, and hence as we know the magnitude of the
earth's orbit we can calculate the distance of the star. The difficulty
is that the apparent ellipses are so minute that it is in very few cases
possible to measure them.

[Illustration: Fig. 54.--The Parallactic Ellipse.]

The distances of the Fixed Stars thus tested are found to be enormous,
and indeed generally incalculable; so great that in most cases, whether
we look at them from one end of our orbit or the other--though the
difference of our position, corresponding to the points marked January
and July in Fig. 54, is 185,000,000 miles--no apparent change of
position can be observed. In some, however, the parallax, though very
minute, is yet appr