"What is a planet?" asked Harry.
"A planet is just like this earth we are living on, and only shines with
the light it borrows from the sun. If we lived on planet Mercury, and
could look at our earth, we would see it shining like a bright star in
the sky; but all the light comes from the sun."
"Do we live on a star, then?" asked Nellie, her little eyes wide open
with amazement.
"No; we live on a planet. We could not live on a star, as a star is
blazing hot. That is the difference between a star and a planet. A star
is hot and bright and shining and gives light to the planets, if it has
any. Planets are little globes like the earth that circle around the sun."
"Then the sun must be a star," said Harry, "as you told me yesterday
that it is very hot."
"That is right," said Mary; "and every star in the sky is a sun."
"And has lots of weensy-teensy planets going all around it?" asked Nellie
excitedly.