"What makes it twinkle?" asked Harry. WHY THE STARS TWINKLE. "When we look at the stars we have to see them through the great ocean of air that surrounds the earth," replied Mary. "Like the Atlantic Ocean, when the ocean of air is disturbed there are waves, and we have to look at the stars through the waves. That is why their light seems to dance about so. When the air is still then the starlight is steady, but when it moves the stars twinkle. If we could go to the moon, where there is not any air, we would not see the stars twinkle." "Then I should rather stay here," said Harry, "because I like to watch them dancing about. They seem so merry, I am sure they are laughing at us, sister. Is there a story about Sirius?" "It is part of a group of stars named the 'Great Dog,'" she replied; "and higher up you will see the 'Little Dog.' These are the hounds that Orion always took with him when he went hunting. They seem to have even followed him to the sky. [Illustration: THE GREAT DOG.] "Sirius is also known as the Dog-star, because when it was seen by the Egyptians in the east just before dawn it was thought to announce the overflow of the Nile. Therefore the Egyptians watched this star, which warned them, like a faithful dog, of the coming deluge. It was their watch-dog or sentinel. "Now I am going to tell you about the Twins, two brothers who loved each other dearly while on earth. They were named Castor and Pollux. Castor was killed in battle. Pollux could not bear to remain on earth without him, so Jupiter placed him in the sky next to his brother. [Illustration: THE HEAVENLY TWINS, CASTOR AND POLLUX.] "If you look through the glass you can see that Pollux is a golden-yellow star and Castor has a green tinge." "Are all the stars colored?" asked Harry. THE FLOWERS OF HEAVEN. "Yes," replied his sister, "and they are as varied in color as the flowers of the earth. The stars may be called 'The flowers of heaven.' Longfellow says so beautifully: "'Silently, one by one, in the infinite meadows of heaven Blossomed the lovely stars, the forget-me-nots of the angels.' "Some of the natives of Australia believe that when the flowers die on earth they rise on the winds and float away to the fair fields of heaven, where they flourish forever in immortal beauty. We cannot see the colors of these flowers of heaven very well, on account of the air that surrounds the earth. If it were removed, then the dark sky would seem to be covered with starry flowers of all the colors of the rainbow." "How beautiful!" said Harry thoughtfully. "How I wish we could see them that way!"