The Outer Planets
Well, as I said before, our understanding of our Solar System has changed dramatically in the past 15 years.

When I was a kid, a hundred years ago it seems, everything was almost comfortable, in that we had nine planets, most of which had one or two or four moons.

Neptune

WEATHER ON NEPTUNE

I said almost comfortable because the orbit of Neptune was wrong. It was if some other big planet outside of Neptune’s orbit was pulling on it.

We still don’t know what causes this.

We also thought Pluto (discovered in 1936) was a planet.

A few years ago, and this is still up for debate, Pluto was demoted and is no longer considered a planet but is now a “minor planet”. Why? Because in the last 15 years, we’ve discovered dozens of Pluto-like objects in orbit around our sun. We've also discovered hundreds of thousands of minor planets, like Ceres.

It’s hard enough to remember the names of the eight: This will help:

My Very Energetic Mother Just Served Us Nachos.

But what does the word planet mean? And what is a planet?

Mars from Hubble

The first use of the word planet came from ancient greek astronomers who had nothing better to do at night than drink wine and star gaze. If you can go camping under a dark sky and star gaze, you’ll know what I mean. Then imagine living your life that way. The word “Planet” comes from the ancient greek word “planetes” which mean traveller.

To the greeks, the stars stayed still but the planets moved. They could make out 5 or 7 “travelers” depending on who you ask:, Mercury, Venus, Mars, Jupiter, Saturn, our some added our Moon and the sun.

There were some amazing people as they had no instruments to enlarge their view, and two major theories evolved.

The first (which stuck) was that everything revolved around the Earth. This theory is called
Geocentric. It was adopted by the Roman Empire, and before you think you know it all, remember that we still refer to sunrise and sunset, where in fact, we are rising and setting. Try using Dawn and Dusk instead.

Two important astronomers who did not concur with the geo-centric view were
Hipparchus and later, Eratosthenes.

These gentlemen calculated that in fact we rotate around the sun, as do the other travelers. We are
Heliocentric.

Enjoy the views and stories of the planets in the links below.