Our+Solar+System

An introduction to our solar system


There are eight planets in the solar system, in the order shown above. A useful Mnemonic for remembering the order of the planets is:


 * M**y **V**ery **E**asy **M**ethod: **J**ump **S**traight **U**p **N**ow!

In addition, as there are two 'M's (for Mercury and Mars) and which planet goes with which M can be remembered because "you should never put your Mars bar near the Sun - it will melt!"

//**Teaching idea**: Hand out cards to the students with one of the planets on (so each student is a planet). Get the students to say the Mnemonic while standing and then to jump up at the end. Then have them rearrange themselves in planetary order (could make sure that there are more in the Gas giant groups as they are so much larger).//

The planets all orbit the Sun in elliptical orbits. An ellipse is a slightly flattened circle, a bit like a slice through an egg.

The planets of the solar system can be divided into two parts, the inner four planets (Rocky Neighbours) and the outer four planets (The Gas Planets). These two parts are separated by the asteroid belt - a region that contains billions of rocks of irregular shapes. In addition, there is a further band of rocks outside the orbit of Neptune, called the Kuiper Belt (also know as the solar system's final frontier). Much further out from even that is the Oort Cloud, a halo of ice and dust left over from the formation of the solar system (Asteroids, Comets, the Kuiper belt and Ort cloud).

The picture above gives an idea of the rough size of the planets relative to one another, but it does not correctly show the distances that the planets orbit the Sun. You can get some idea of the distances involved here (link). An alternative image of the solar system is below (not to scale, although the relative sizes of the planets are approximately correct (although not to scale, and Pluto, a dwarf planet (Dwarf Planets), is shown)).

Aside/Extension: but why do planets orbit at all?
(External link to MinutePhysics youtube channel)

media type="youtube" key="uhS8K4gFu4s" height="315" width="560"


 * IAU definitions of planets and dwarf planets**

A planet is:
 * an object that orbits a star and
 * has sufficient mass so that gravitational forces produce an approximately spherical shape //and//
 * it is large enough to sweep its area of space clear of debris during its formation.

A dwarf planet is:
 * an object that orbits a star, and
 * is big enough to have an approximately spherical shape, but
 * not so big that it sweeps its area of space clear of debris.