SJAA

Ephemeris

How To Write Your Own "Mooning" Column

David North


So you want to write a Moon column? Nothing to it.

First, open your RASC Observer's Handbook to the appropriate month (June in this case). Check the libration dates. Hmm. The east limb (Crisium) is most exposed at just before first quarter (on June 18), which means the maria will be at maximum visibility (contrast from overhead light). This might be worth mentioning.

The west limb (Orientale) is librated best at third quarter (June 6)... bingo! First and third quarter are both good for looking at maria/highland contrasts at strong librations. Could be a theme... but too early to say.

The northern libration looks uninteresting, but the southern libration is best near full moon, which is also good for seeing things on the terminator. This is a good libration month - remember to suggest folks look at the south on the days near full.

Okay, any other weird lunar events listed? There are several "moon near this and that" events (planets and stars) with three occultations not visible from the U.S. Nah, don't mention them.

Whoa, wait a minute. Here's something. The greatest northern declination for June is on the 14th, just after new moon. Now that's neat!

Thing is, when the moon is highest in its orbit just after new, you get the best opportunities to see a young moon. They will both be crashing into the horizon at very steep angles, leaving quite a bit of "moon elevation" even after the sun has set.

So this month is a great one to scan with binoculars just after sunset to see if you can catch a tiny sliver in the sky. Only takes a few minutes, and then it's off to the deep sky...

Make sure you have a good western horizon.

Of course, it also means this is a good month for looking at the early moon features over the next few nights. In some ways, this is the best time for catching the waxing views of the Gang Of Four, so maybe that should be the discussion theme for this month.

The Gang Of Four?

This is four monster craters on the same line of lunar longitude (roughly 60 degrees east) that emerge into best viewing between two and four days after new, depending on libration and such. Let's see when they will just open up...

How do we do that? Go to Akkana's "Hitchhiker's Guide To The Moon" and look at terminator placement. We know the craters are fully open when the terminator reaches 55 degrees east. Let's see ... that happens at a bit before midnight on June 15. Perfect!

So the idea is to let people know this very young moon will also be showing these four cool craters, and that there's a reasonable chance to catch them in the act due to the extreme elevation.

What's so great about the Gang Of Four?

For one thing, just their arrangement. They are evenly spaced and almost identical in size.

In order from the equator running south they are Langrenus (a new, well-formed crater with excellent secondary impacts nearby) Vendelinus (a ruined old mess with a nicely formed crater - Lame', as in something Ava Gabor might wear -smacked into its rim) Petavius (youngish, with the flat out most obvious rille on the moon running out from its central peak, looking like a minute hand on a railroad watch) and Furnerius (an older crater with a wonderfully complex rille system in its complex interior).

They are a microcosm of mooniness. Comparing them you can see the effects of age, and of time of formation. You can see rilles, secondaries, terracing, mass wasting, superimposition... it's a convenient classroom of similar craters of different ages and circumstances.

Suggest folks compare and contrast, and see what they can figure out just from looking. Use noggins, etc. All good fun.

Okay, so that's about it for June. There are lots of other things that could be said, but space and time require a halt somewhere.

Anyway, that's pretty much how you do it.

Oh, wait a minute. I forgot to mention how you add the flowery language and wax poetic now and then to lamely attempt to convey something of the aesthetic effects of these sights.

Then again, "Ooooo" and "wooo!" really work pretty well too.

Oh, by the way, the name Gang Of Four? Not official; I made it up. Based on the folks who took over China after Mao died. Just liked the way it sounded and it seemed to fit these craters for some reason. I suppose making up stuff like that is also part of putting together a column like this.

It's not like I really know. I'm making this up as I go along.


David North; last updated: October 04, 2007 Prev Next