SJAA Ephemeris December 2012 | SJAA Home | Contents | Previous | Next

The Shallow Sky

A month of subtle challenges

Akkana Peck


Jupiter hits opposition on the 2nd of December. It’s in Taurus, about three degrees away from globular cluster NGC 1657 as December opens. That’s probably too far away to get them both in the same field in most telescopes, but give it a try in binoculars if you have a good dark sky. If you manage to see both of them, watch over the course of several nights – it’s impressive how fast Jupiter moves during the opening week of December relative to the cluster and the stars of the Hyades.

While you’re watching Jupiter, don’t forget its moons. Transits of the four large Galilean moons across Jupiter’s disk are always entertaining. But for a greater challenge, try looking at the moons themselves. See if you can tell them apart. Ganymede is relatively easy: it’s so much larger than the others, resolving easily into a disk where the other three may not. Io you can often tell by its color, redder than the other three. Europa and Callisto can be much harder to tell apart, at least when they’re close to Jupiter – Callisto gets much farther away from the planet than Europa does, so that can be a clue. What other clues can you find to distinguish the moons?

As long as we were talking about seeing Ganymede’s disk: a few months back, amateur astronomer and photographer Emmanuel Kardasis, from Athens, Greece, did a lot more than just see a disk. Stacking CCD images he made with an 11” telescope (looks like a C11 on his website, though he doesn’t say explicitly), he made and published an albedo map of Ganymede. It’s not highly detailed ... about like what you might see on Mars in anything but an especially good opposition. Kardasis has other astrophotography worth seeing, including an albedo map of Mars and some great Jupiter images, on his website at

Not up to making albedo maps, but still want a challenge? Ceres is also at opposition this month. Like Jupiter, it’s in Taurus; but it’s at the other end of the constellation, out near the right horn of the bull. It’s roughly magnitude 6.7, and it’s located roughly halfway between two fifth magnitude stars, Tau 125 and double star Tau 132A. There’s another 6.7th-magnitude star right nearby, and it and Ceres make a distinctive pattern between the two fifth magnitude stars that might help in finding it.

Mars is visible early on December evening, but it’s so low and small that it’ll be tough to see much detail. If you want to see Martian detail this month, you’re best off checking the Curiosity rover’s website. As I write this, Curiosity has been looking for evidence of methane in Gale crater, with disappointing results. You may remember the Mars methane mystery from last year. The media got all excited over evidence that there was significant methane in Mars’ atmosphere, fluctuating on a seasonal basis, or perhaps even faster. That would mean new methane was being generated somehow – perhaps by processes involving life, since here on Earth, most methane is generated by living organisms.

But methane is tough to measure, especially from a distance through two atmospheres. So hopes have been pinned on Curiosity’s on-the-spot measurements. So far, sad to say, the rover hasn’t found any.

Of course, the Curiosity team will keep looking, and could still find something ... but it’s looking a little less likely.

Uranus and Neptune are both well placed for early evening observation.

Catch them fairly early, since Neptune sets before 11pm (Uranus lasts a few hours longer). Pluto isn’t visible this month.

Early risers get a nice naked eye show in the December morning sky. Venus is there all month, and Mercury shows well in the first half of December. On the morning of the 11th, the two planets make a nice triangle with the crescent moon.

Saturn, too, is best positioned for early risers. The ringed planet has been in the news a lot lately, not for its rings but for its storms. Alas, the showiest parts of the recent Saturnian storms are only visible in infrared, so you probably won’t see much with your telescope. But if you have a CCD rig that’s sensitive to IR, this is a good time to get it out and see what you can do.


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