that body. Distance known, the proper motion of the
star, hitherto only to be reckoned as so many seconds of
arc, may readily be translated into actual speed of progress;
relative brightness becomes absolute lustre, as
compared with the sun; and in the case of the double
stars the absolute mass of the components may be computed
from the laws of gravitation. It is found that
stars differ enormously among themselves in all these
regards. As to speed, some, like our sun, barely creep
through space--compassing ten or twenty miles a second,
it is true, yet even at that rate only passing
through the equivalent of their own diameter in a day.
At the other extreme, among measured stars, is one
that moves two hundred miles a second; yet even this
"flying star," as seen from the earth, seems to change
its place by only about three and a half lunar diameters
in a thousand years. In brightness, some stars yield to
the sun, while others surpass him as the arc-light surpasses
a candle. Arcturus, the brightest measured star,
shines like two hundred suns; and even this giant orb
is dim beside those other stars which are so distant that
their parallax cannot be measured, yet which greet our
eyes at first magnitude. As to actual bulk, of which
apparent lustre furnishes no adequate test, some stars
are smaller than the sun, while others exceed him hundreds
or perhaps thousands of times. Yet one and all,
so distant are they, remain mere disklike points of light
before the utmost powers of the modern telescope.