In my Constellation Series, I talked about all constellations discussed by Hellenic astronomer Ptolemy. Ptolemy set out forty-eight constellations, based in Hellenic myth, of which some are still recognized to this day, and others got broken up or otherwise rearranged or added in the years that followed. As a addendum, I also made a post on the major planets and the stories from Hellenic mythology behind them. Did you know, though, that much more in the sky is named after Hellenic mythology? Today we talk about the categories of minor planets and their Hellenic mythological roots.

A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Minor planets can be dwarf planets, asteroids, centaurs, trojans, Kuiper belt objects, and other trans-Neptunian objects. You probably know what a dwarf planet is (a tiny planet, basically), and an asteroid (a space rock) is probably also familiar. A trans-Neptunian object is (basically) anything big in space that is farther away from the Sun than Neptune. Like Pluto. A Kuiper belt object is basically a very large asteroid belt and it has nothing to do with Hellenic mythology. The others, however, do. These are the ones you perked up at if you're like me. Let's run by them, shall we?

A centaur is a small body that orbits the Sun between Jupiter and Neptune and crosses the orbits of one or more of the giant planets. Centaurs are among the most mysterious objects in the Solar System. They share characteristics with planets, asteroids and comets, and astronomers have struggled to find one classification that fits them all. That's also where the name comes from: they are a mix of things and thus a class apart. Centaurs were part horse, part human. Centair minor planets have characteristics of planets, asteroids and comets but are none of those. They also "jump" between planets, making them unstable, "wild" entities.

A trojan is a minor planet or moon that shares the orbit of a planet or larger moon, wherein the trojan remains in the same, stable position relative to the larger object. Did your brain fog up? Let's drop the science words. Every planet revolves around the Sun in an endless loop. Planets do that but almost all other things in the orbit of something else rotate as well. Moons, like our one moon, revolve around the planet they belong to, for example. Trojans don't move. They stay relatively in the same spot between a planet and the Sun.

While a planet rotates around the Sun (and usually around its own axis), it always holds a "line of sight" to the Sun, so to speak. You can always draw an imaginary line from the Sun to a planet. By doing so, you automatically divide the area into two parts, like the two sides of a soccer field--or a battle field. Around Jupiter, these areas are called "L4" and "L5". Here's a diagram to make things a little clearer:


Sun ----------------------- planet


The L4 region is known as the Hellenic "camp", while the L5 region is known as the Trojan "camp". Jupiter is the planet that named the Trojans as this is where they were first discovered. It was long believed Jupiter was the only planet to have Trojans (it has about 6000), but there are others. Mars has four, Neptune has seventeen, and our humble planet has a single one.

There are a lot of minor planets known to us, and a lot of them were named after famous people and creatures from Hellenic mythology. Tomorrow I'll list a few of my favorites.