SJAA Ephemeris December 2010 | SJAA Home | Contents | Previous | Next

The Shallow Sky

Full of Moon

Akkana Peck


Although there are plenty of planets to watch in December – Jupiter high in the sky, Uranus and Neptune visible in the early evening, Mercury low in the evening during the first half of the month, and Venus and Saturn in the morning – the real news this month is all about the moon.

We'll see (weather permitting) a spectacular lunar eclipse on the evening of Monday December 20th, perfectly placed with the moon way up at 75 degrees. The moon will be just above the raised arm of Orion, as though the full moon were a tennis ball Orion is about to lob right through the Hyades.

The penumbral eclipse begins at 9:29pm PST. This stage is very subtle and you probably won't see any difference, but it doesn't hurt to try! Partial eclipse begins at 10:32, with totality lasting from 11:40 p.m. until 12:53 Tuesday morning. As usual, the moon is offset within the Earth's shadow; the north limb of the moon will be brighter than the south during totality.

It's been a while since we've had an eclipse this good! But the eclipse isn't the only moon news. Our satellite has been in the science press quite a bit over the past month.

For instance, the Lunar Orbiter Laser Altimeter (LOLA) team just announced that they'd found the highest point on the moon. Unfortunately, you can't see it: it's on the lunar far side, a visually undistinguished gentle rise near Engel'gardt on the fringe of the Korolev plain. It's 10,786 meters (35,387 feet) above the lunar datum – an arbitrary point chosen to act as "sea level" on the moon. For comparison, Everest is 8,848 meters above Earth's sea level.

Prior to LOLA, the highest point on the moon was thought to be Beta in the Leibnitz Range, at 36,000 feet. That one you *can* see, at least in months when there's a good western libration so Mare Orientale is tilted toward us. December isn't ideal but it isn't bad. On the 20th while you're waiting for the eclipse to start, swing over to the southwestern limb of the moon, get out your Rukl and turn to chart 61 and libration chart VII. Rukl doesn't label the Leibnitzes, but they're near Valles Bouvard, just outside the southern edge of the Cordillera mountains.

Okay, so the Engel'gardt area isn't the most impressive lofty peak you've seen. But there was other moon news last month.

"Water on the moon!" screamed the headlines. The results came from several new papers analyzing the results of the LCROSS impact. Remember LCROSS? It crashed into Cabeus crater near the moon's south pole in October 2009, and we were all disappointed that it didn't produce a big visual plume. But it did produce lots of spectral data, which has finally been processed and published – and it shows more water than expected. We're not talking oceans here: the area around Cabeus is a little wetter than the Sahara desert. But that water is thought to be in the form of ice grains, which would be relatively easy to separate from the surrounding rock.

Most articles included teasers like "There are oases of water-rich soil that could sustain astronauts on the Moon" (BBC) and "The moon is pockmarked with cold, wet oases that could contain enough water ice to be useful to manned missions" (Wired). It's all about the manned missions – not about the other interesting elements that turned out to be bound up with that water.

Several sites quote Dr. Anthony Colaprete: "In about a tonne of material, you're talking 11-12 gallons of water that you could extract.” (Note the BBC spelling of tonne.) Curiously, when I went back to check, that quote had been removed from both the BBC and Wired stories. But you can still find it in the Google cache. Wonder what that means?

Am I the only killjoy who reads that and envisions small lunar bases surrounded by mountains of slag and tailings? Is the moon going to look like the Kaiser Cement quarry over by Stevens Creek, the big bare spot in the mountainside that you can't help but notice when you fly out of San Jose? 12 gallons doesn't sound like very much compared to the needs of a working lunar base.

But how much rock is a ton of rock? Basalt, the rock making up the lunar maria, has a density of around 3 grams per cubic centimeter. A ton is about 907,185 grams, so a ton of basalt works out to only about a third of a cubic meter, or about ten cubic feet.

Astronauts on the ISS use about 3 gallons of water per day – that's mostly for necessities like eating and drinking, not luxuries like dishwashing and bathing that you might want for an extended stay. We use more like 35 gallons down here on Earth. But say you have a lunar crew of 5 and they can keep to a very conservative 5 gallons/day each, and they don't need water for any industrial uses. That's about 750 gallons/month, so you'd need somewhere around 65 tons of rock, 650 cubic feet or about 24 cubic yards, or a cube about 8.6 feet on a side.

Okay, that isn't that big a slag pile after all. Maybe I'm the dense one.

Oh! One last news item, and it's not even about the moon. Remember poor Spirit, the plucky Mars rover, stuck in one place but still doing useful science? Recently published results show that Spirit's spinning wheel, while it wasn't enough to get her out of her sand-trap, revealed what looks like relatively recent signs of damp soil.

Spirit stopped communicating in March with what appeared to be a low-power fault. But there's still hope that with increasing sunlight she may be able to recharge her batteries and resume communication.This month is the month the Rover drivers hope to be able to re-establish communication. Cross your fingers for Spirit! You can check on status of both Mars rovers at

Ed. Note: Photo is courtesy of NASA/GSFC/Arizona State University. More photos available at!.html


Previous | Contents | Next