Saturday, September 25, 2010

Celestial Choreography.

Since I'm going up to Mauna Kea tonight, I thought I'd put up some pictures I took the last time I was there. The first one is very cool, because it shows one of the phases of Venus. I don't recall ever having seen these before, so it was an awesome experience for me. Seeing such phases is one way to tell that Venus orbits closer to the Sun than we do.
Crescent Venus.
North is roughly off to the right in the picture. Note the chromatic aberration present in the image, visible as a slight separation between the most red and most blue parts of the image.

The second picture is of Jupiter, the behemoth of the solar system.
North is up in this picture. You can clearly the North Equatorial Belt near the top of the planet. The corresponding South Equatorial Belt has been missing for several months now. It will no doubt return as it always has sometime in the next few years, but for now you get to see the planet in a little more lop-sided version.

While checking up on Jupiter, I learned a rather funny fact about the Trojan asteroids. The Trojan asteroids are two groups of asteroids that are caught by gravity at Jupiter's L4 and L5 Lagrange points. This means they orbit the Sun roughly 60 degrees ahead of and behind Jupiter in its orbit. I had never known why they were called the Trojan asteroids before, but it turns out it's because the first one discovered was called Achilles, and by convention every one discovered since (all 4,076 of them) have been named after figures in the Trojan War from the Iliad. In fact, it's even more structured than that; the asteroids orbiting ahead of Jupiter are named after people in the Greek camp, while those following Jupiter are named after people in the Trojan camp (although this rule was suggested after they'd found a few, so there are two exceptions: Patroclus is found in the Trojan camp, and Hektor, the largest of them, in the Greek camp).

As an interesting aside, the word trojan has now entered the astronomical lexicon to refer to any body trapped 60 degrees ahead or or behind another in its orbit. Thus, there are other trojan asteroids (note the lowercase spelling); several associated with Mars, and a few with Neptune. There are even 4 known trojan moons, all in orbit around Saturn, which is where three moons share the same orbit, one large one in the middle with two smaller flanking ones behind and before.

A hui hou!

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