"I wonder how many stars there are in the sky, sister," said Harry. "Do
you think we could count them?"
"I read somewhere," replied his sister, "that the stars are as plentiful
as the sands on the seashore. Still, in the whole sky, the number bright
enough to be seen without a telescope is only from six to seven thousand
in a clear, moonless sky. With an opera glass you can bring the number
up to one hundred thousand. A small telescope can show about three
hundred thousand, while with a telescope such as the one at the Lick
Observatory the number would be nearly one hundred million. But it is
possible to photograph the stars, and millions of stars have had their
pictures taken. Probably we would never have known anything about them
but the camera caught them, and now they are being named and labeled,
so that they cannot escape us again. In fact, some of the stars are so
far away that if we had not captured them in this way they would have
remained hidden to us forever."
"What do you mean, sister?" said Harry, his eyes filled with surprise.
"I mean, dear, that some stars are so far away that their light has
not yet reached us. Don't you remember what I told you about Jupiter's
moons: that they are so far away that light takes about half an hour
in coming from them to the earth. Well, the stars are hundreds of times
as far away as Jupiter's moons. So far away are they that even from the
nearest--a star seen in the southern hemisphere--light takes four years
and four months in reaching us, although light travels more than 186,000
miles a second."