In a _____ model the Sun, not the Earth, is in the center and all other objects including the Earth orbit the Sun. In this model the Earth is moving in two ways. It revolves arround the Sun and it also rotates on an axis.
Because the moon's period of rotation is equal to its period of revolution, that is to say, because the moon takes the same amount of time to spin as it does to orbit the earth, we from the earth only ever see one face of the moon.
The solar system came into being about 4.5 billion years ago when a cloud of interstellar gas and dust collapsed resulting in a solar _____ , a swirling disk of material that collided to form the solar system.
Thousands of years ago, ancient astronomers looked up at the sky and realized that some of the things they thought were stars were moving in ways they didn't expect. They called these errant objects _____ , a word that means wandering stars.
When Pluto was discovered in 1930, it was named the 9th planet of the solar system. More than 75 years later, that planetary status devoked and Pluto was demoted as _____.