# Solar System Model

Most science fairs will have at least one model of the solar system. It usually has painted balls hanging from strings to show the planets in the right order with Mercury closest to the sun and Pluto farthest out. That is all the model shows.

Many students have learned a sentence to help them remember the right order of the planets so they don't really need this model. One sentence to help remember the planets is "My Very Educated Mother Just Showed Us Nine Planets." The first letter of each word is the first letter of a planet. Starting near the Sun, the planets then are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

In 2006, the International Astronomical Union met to talk about the definition of a planet. It decided that an object in our solar system must have several properties to be called a planet. It must orbit the sun, it must be large enough to take on a spherical (ball-like) shape and it must have a strong enough gravity field to have cleared the area near its orbit of other objects. Pluto has other objects close to its orbit so it is now called a dwarf planet, not a major planet. Eris, which was discovered in 2005 and is larger than Pluto, is also called a dwarf planet. Ceres, which is the largest object in the asteroid belt, is the third and smallest dwarf planet in the Solar System. Most Websites and models have not yet been changed to show this new classification.

Wouldn't it be really cool to make a model that compared the planets' sizes? Or what about a model that shows how far apart the planets are? Lets look at how you could make some models of the solar system that really show something.

The Exploratorium has a Web page where you can make a scale model of the sizes of the sun and planets by putting in one size, for example a 18 inch ball for the sun, and a Java Script will figure out the sizes of the other objects.

A separate model to show how far apart the planets are can be set up using a small marble as the sun. The distances below will tell how far it is to the next planet. One way to do this is to take a big ball of string and use a permanent marker to mark the distances on the string. This model does not show the sizes of the planets. You could write planet names on pieces of paper and have a student stand with the label where each planet should be. In this model, Pluto is about 60 meters or 66 yards from the sun.