"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.
STORY OF PLANET MERCURY.
"Some of them have, I am sure," said Mary. "But now we are running along too fast, and I must tell you about our own sun first, and its nearest planet Mercury. Well, Mercury is a very warm little world, and it gets so near the sun that sometimes it is about nine times as warm as here, and at other times it is only four times as warm. You see, Mercury does not go round the sun in a perfect circle, so at times it is farther away than at others. Now, the sun is like a great fire in the sky, and the nearer we go to it the warmer we are. How would you like to live on a little world where it is nine times warmer than it is here?"
"I should not like it at all, would you, dollie?" said Nellie; "we would roast if we went to world Mercury."
"But we don't know whether there are any people there," continued Mary, "and if there are, they might not mind the heat at all. You can get used to the heat, just as Uncle Robert did when he went to India. Don't you remember how he felt the change when he came home, and how he shivered? He missed the heat just as we would suffer from it if we went to India for the first time."
