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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?