Key Idea 1: The day, the month, and the year are determined by the motions of the earth and moon.

Key Idea 2: The solar system contains planets, moons, asteroids, and comets with the sun in the middle. Astronomers use various methods to gather information concerning the solar system, including telescopes and space probes equipped with cameras and spectrometers.

Key Idea 3: The universe is composed of galaxies which contain stars, planets, asteroids, comets, gas and dust.

Key Idea 4: The universe began in an explosion, called the Big Bang, about 14 billion years ago.

Key Idea 5: Every object exerts a gravitational force on every other object. The strength of this force depends on the mass of the two objects and the distance between them.