阅读理解

    As long as people live on Earth, we will never stop looking up at bright stars in the night sky.

    We are always trying to understand the universe. Astronauts know that not all stars are the same. Some are almost as old as the universe itself, and others may be born just now. They are in different colours, blue, white, yellow and red. Some shine brightly in the sky, while others areVisibleonly with special tools. You can't see them with your eyes. Some stars run through space in pairs or groups, while others move alone.

    One of the most important ways that scientists group stars is by size. In the early 20th century, just World War I, astronauts began to put stars into two main size groups.