Download Astronomy Unit – Part 3: The Planets Terrestrial Planet – the four

Astronomy Unit – Part 3: The Planets
Terrestrial Planet – the four small, dense, rocky planets that orbit closest to the sun
Astronomical Unit (AU) – the average distance between the sun and the Earth, or 150 million km.
Prograde Rotation – counterclockwise spin of a planet.
Retrograde Rotation – the clockwise spin of a planet. (Venus)
Gas Giant – the four outer planets with deep, massive gas atmospheres which are made of mostly
hydrogen and helium. No surface to stand on.
Planetary Ring – A disk of material that circles a planet and consists of orbiting particles
Dwarf Planet – a celestial body that orbits the sun and is round because of its own gravity.
Kuiper Belt – a region of the solar system that begins just beyond the orbit of Neptune and contains
small bodies made mostly of ice.
Kuiper Belt Object – any of the minor bodies in the Kuiper Belt
Comet – small body of ice, rock, and dust that follows a highly elliptical orbit around the sun
Asteroid – small, irregularly shaped, rocky object that orbits the sun.
Oort Cloud – a spherical region that surrounds the solar system and extends almost halfway to the
nearest star
Meteoroid – a sand-grain to boulder sized, rocky body that travels through space
Meteor – a bright streak of light that results when a meteoroid enters the Earth’s atmosphere
Meteorite – a meteoroid that reaches Earth’s surface without burning up