SPECIAL NOTE:  I may need to change this lesson soon because some scientists got together and decided that Pluto isn't a planet anymore.  But, I heard that a bunch of other scientists are arguing about it.  So, for now, I'm going to leave things the way they are.

Our solar system has 9 planets that orbit a big star called the Sun. (An orbit is the path that a planet moves through.) All the planets orbit the Sun in elliptical paths. (An ellipse is just a stretched out circle.)

All the planets take different amounts of time to get all the way around the Sun.  Our Earth takes a year to make one complete orbit.  In fact, that's how we decided how long a year should be - it's the length of time it takes us to get all the way around the Sun!

Also, all the planets spin while they move around the Sun... Just like tops!

There is another mess of stuff that orbits the Sun... We call it the Asteroid Belt and it is just a bunch of really big rocks.

Here's a picture of all the orbits:

If you need to remember the order of the planets, here's a trick: Just look at the first letters of each planet in order, starting with Mercury and working your way out... 
M, V, E, M, J, S, U, N, P and make up a funny sentence that uses these letters.  Here's one:

Mooing very eagerly, Mary jogged south under nine planets.
(The funny thing is: Mary's NOT a cow!)

How do all their sizes compare? The big yellow circle is the Sun's size and all the others are arranged from smallest to largest. (Man, look how little the Earth is compared to the Sun!)

The inner planets, Mercury, Venus, Earth and Mars are called terrestrial planets. This means that they have a hard surface (rock) to stand on.

Jupiter, Saturn, Uranus and Neptune are called the Jovian planets, since they are all a lot like Jupiter. (Jove was another name for the Roman god, Jupiter). They are also called gas giants. This is because they are made of gas and liquid (but not water). There's no hard surface to stand on!

(Poor little Pluto doesn't get to fit into either of these categories.)

To find out a ton of cool stuff about each thing, just click on its picture below!
There's one thing that we think is the very coolest (not cold) thing in the entire solar system... Can you find what it is?
(Here's a question we've got for you: On which planet is your weight the closest to what it is on Earth?)

The Sun

Mercury

Venus

Earth     Our Moon

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

Sources:
In Quest of the Universe, 2nd ed. by Karl F. Kuhn
Voyages Through the Universe, 2nd ed. by Fraknoi, Morrison and Wolff
Universe by Kaufmann
The Complete Idiot's Guide to Astronomy by Christopher De Pree and Alan Axelrod
The Astronomy Cafe by Sten Odenwald