Maybe many people know the universe is very big. Some scientists thought the universe seems to be rapidly expanding its component galaxies moving ever farther apart. So it's very big. There are many heavenly bodies in the universe. If you stand in space, you will see many beautiful stars, like sun and other planets. And then, let's recognize our solar system. There are eight planets in our solar system. They're Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. T...
