canspice.org

Moons are in the news today, with the release of two press releases looking at planetary satellites in our Solar System.

The first comes from Uranus, where the Hubble Space Telescope witnessed Ariel’s shadow crossing Uranus’ disk. This might not sound exciting, given this sort of thing happens all the time. When this happens here on Earth people flock to see it — it’s a solar eclipse. It happens on Jupiter all the time as well.

But it only happens on Uranus every 42 years. Why? Because Uranus and its moons are tipped by almost ninety degrees. Instead of pointing roughly perpendicular to the ecliptic (the plane that all the planets orbit around the Sun on), Uranus’ axis of rotation is aligned with it. Imagine this happening on Earth — once a year the North Pole would point directly at the Sun, receiving constant light from a Sun that appeared to stay directly overhead. Six months later, the North Pole would be in perpetual darkness.

Equally, every six months the orbit of the Moon around the Earth would line up with the Sun, and the potential for a solar eclipse would happen. An eclipse wouldn’t necessarily happen, as things don’t line up every time (which is why we don’t have an eclipse every 14 days).

But on Uranus, where one orbit around the sun takes 84 years, things line up every 42 years. Luckily for us, an alignment is happening right now!

The second moon-related news comes a little closer to home: our Moon. Back in 2003, the European Space Agency launched SMART-1, a space probe designed to test an ion drive and miniaturized instruments while at the same time examining the Moon. By all accounts it succeeded fantastically. But now its ion drive is all out of juice and the probe has reached the end of its life, so ESA decided to smack it into the Moon. Doing this allows astronomers to find out all sorts of things about the Moon, from the chemical composition of the surface, to the actual physical makeup of the surface (how “dusty” it is, how hard it is).

Because of the vagaries of lunar orbits (the Moon isn’t spherical, so close orbits aren’t easy to calculate), nobody’s exactly sure when SMART-1 is going to impact, but they’ve narrowed it down to three possible orbits. They figure it’s going to hit on September 3 at 05:41:51UT (which is 19:41:51HST on September 2, or 22:41:51PDT on September 2, or 01:41:51EDT on September 3). But the orbit before that, they’re not quite sure about yet.

See, SMART-1 is forecasted to pass a mere 800 meters above the crater wall of crater Clausius. This is close. Real close. Airplanes on Earth fly more than ten times higher than that. Could you imagine standing on the Moon watching this thing come flying overhead? It’d be amazing!

And even cooler, SMART-1 took pictures of where it’s going to impact. Take a look at the hi-res picture. See the diamond on the right? That’s the lowest point in that orbit, and it’s right where the crater wall of Clausius is. How’s that for shaving it close?

The FIA has released the 2007 Formula One calendar. Notable drops are Imola (the San Marino GP, essentially a second GP for Italy) and Nurburgring (the European GP, essentially a second GP for Germany). A welcome return is made to Spa-Francorchamps.

However, all is not fixed just yet. As grandprix.com points out, there’s plenty of room for movement. There’s an odd three-week break between Australia and Malaysia, and apparently the Suzuka track (which lost the Japanese GP to Mount Fuji) is lobbying to get a race near the beginning of the season. Could there be a return to the Pacific GP?

Occassionally I download live concerts. Mostly I go for Tragically Hip bootlegs, but I still troll through dimeadozen and bt.etree.org for bootlegs that look interesting. I do so by using their RSS feeds.

This is where bt.etree.org sucks ass. Their RSS feed is of middling quality. Sometimes you’ll get a full description, with songs played, recording equipment used, some description of recording quality, and other useful information. But more often than not you’ll get something like this:

gm2006-08-25.c34

That’s it. What the hell is that?

dimeadozen, on the other hands, has admins that will ban torrents that don’t have accurate descriptions. It’s a breath of fresh air beside the dungheap that is the bt.etree.org RSS feed.

The International Astronomical Union recently voted on a proposal that would give strict definitions as to what a planet is in our Solar System. The resolution that passed gives the following definitions:

A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

This means that Pluto is no longer a planet, as its orbit is partly shared with Neptune.

Bill Ferris, on the Minor Planet Mailing List, raises an excellent point:

Playing devil’s advocate; I’d like to know how Jupiter, Saturn, Uranus and Neptune meet the newly adopted criteria to be defined as planets.

All have proximate ring systems; Saturn’s being the most extensive and visually dramatic. Jupiter has more than 60 known satellites; Saturn more than 30; Uranus more than 20; and Neptune a baker’s dozen. The giants share their neighbourhoods with material that, in each case, has a total combined mass greater than that of all the known asteroids combined. Additionally, Jupiter shares its orbit with hundreds of asteroidal objects (small solar system bodies) known as trojans.

If the distinguishing characteristic that separates a planet from a dwarf planet is having “cleared the neighbourhood around its orbit,” how do the gas giants meet that criteria? Their neighbourhoods are nothing if not well-populated.

He’s right. The neighbourhoods around the gas giants are quite crowded. Because of this, all four fail the “it has cleared its orbit of other objects” test, and therefore all four gas giants are, in fact, dwarf planets.

So to remember the planets in the Solar System, just remember this simple mnemonic:

My Very Educated Mother.