The Solar System
A solar system consists of a central star (or stars in binary systems) and everything in orbit around it,
including planets (and their moons), the asteroids, comets, and meteors.
The orbits are elliptical – an elongated circle or oval.
Star
a giant ball of gas that produces heat and light due to nuclear reactions
The Sun is a star made of mostly hydrogen and helium.
Our sun holds 99.8% of the mass of the solar system.
The gravitational attraction of the Sun keeps the other objects in their orbits
Planet
a round object that orbits a star and has cleared other objects from its orbital neighbourhood.
Inner (Terrestrial) Planets = Mercury, Venus, Earth, Mars
Planets that are mostly solid or semi-solid rock
Outer (Gaseous) Planets = Jupiter, Saturn, Uranus, Neptune
Dwarf Planets = Pluto, Ceres, Eris
Planets have not cleared the path of their orbit and are usually smaller than Mercury
http://solarsystem.nasa.gov/galleries/tilted-eris
Asteroids
rocky, airless, irregularly (not spherical) objects that orbit a star that are smaller than dwarf planets
Asteroid Belt – orbital area between Mars and Jupiter that contains thousands of asteroids
The orbits of some asteroids cross the orbits of other planets, including Earth.
Comets
“dirty snowballs” made of dust and frozen gases with highly elongated elliptical orbits.
Halley’s Comet – periodic comet that return’s to Earth’s vicinity every 75 years
Meteors
Rock fragments that enter the earth’s atmosphere and appear as “shooting stars”
Most burn up before they reach the surface.
Meteorites
Pieces of meteors that land on the Earth’s surface
Astronomical Unit
the average distance between the Sun and the Earth.
(1 AU = 150 000 000 km)