Image from NASA

ORDER OF THE PLANETS

There is a very simple way to help remember the order of the planets.

I’m not talking about a song or poem. There are a few of these, but then you’re just memorizing a song instead of memorizing the order of the planets. You’re still memorizing.

What I have in mind is a simple trick. It’s a mnemonic device to help remember the order of the planets in our solar system.

S-U-N

Our solar system begins and ends with S-U-N.

The beginning is easy: The sun is in the middle.

But it also ends with S-U-N. The last three planets of the solar system are Saturn, Uranus, and Neptune.

Take the first letter of Saturn (S), Uranus (U), and Neptune (N), and you see how it ends with S-U-N.

As an astronomy teacher, I see firsthand that many (university!) students easily forget whether Uranus comes before or after Neptune, and whether Saturn comes before or after Jupiter.

I explain how the solar system both begins and ends with S-U-N. Students who remember this invariably get the order of the planets correct.

You naturally study the order of the planets from beginning to end. This way, students tend to learn the beginning better than the ending.

Also, earth is near the beginning (third planet from the sun). Since earth is the most familiar planet, it’s easier to remember Venus and Mars because they are closest to the most familiar planet.

The biggest problem, in my experience, is how the solar system ends. Remember that it ends with S-U-N, and you’ll know that the last three planets are Saturn, Uranus, and Neptune.

Here is the complete order:

• M-Mercury
• V-Venus
• E-Earth
• M-Mars
• J-Jupiter
• S-Saturn
• U-Uranus
• N-Neptune

What happened to Pluto? Pluto turns out to be one of very many Kuiper Belt objects. There are many icy bodies in the Kuiper Belt, beyond Neptune, with comet-like compositions (in fact, many comets that we see from earth spend much of their time in the Kuiper Belt, or beyond that in the Oort Cloud). There is another belt, called the Asteroid Belt, filled with rocky bodies between Mars and Jupiter. Pluto is a large Kuiper Belt object, smaller than any planet. Pluto is one of the dwarf planets in our solar system. Pluto is not even the largest Kuiper Belt object. That honor belongs to Eris.

Image from NASA

Here is how I teach the order of the solar system:

• S-Sun
• M-Mercury
• V-Venus
• E-Earth
• M-Mars
• A-Asteroid Belt
• J-Jupiter
• S-Saturn
• U-Uranus
• N-Neptune
• K-Kuiper Belt
• O-Oort Cloud

The Oort Cloud is a very large, spherical shape with occasional icy bodies that lies beyond the Kuiper Belt. The icy bodies that comprise the Kuiper Belt lie more in a plane that matches the solar system, whereas the Oort Cloud is spherical. The Oort Cloud is much wider than the Kuiper Belt.

Image from NASA

Copyright © 2014 Chris McMullen, author of math and science books (including An Introduction to Basic Astronomy Concepts)