The universe is made up of all matter and space, including astronomical objects like stars, planets, satellites, comets, and asteroids. Originally, all matter was in one place and exploded in an event called the Big Bang, spreading matter outwards to form the astronomical objects seen today. Galaxies contain billions of stars and objects, including the Milky Way galaxy which contains our solar system orbiting the Sun along with eight planets. The document goes on to define stars, planets, satellites, asteroids, comets, and meteors. It also describes geocentric and heliocentric models of the solar system and provides details about the Earth, its rotation, revolution, and the cause of seasons and the moon's phases.