SJAA

Ephemeris

Mooning

Dave North


The lunar event of the month will no doubt be the occultation of Aldebaran at about 11:35 pm on the 26th. It's a very favorable night; the main event will take place in the southwest with the moon still about 40 degrees up, so it will be very easy to see.

There's no reason to wait until that late to start your run, though, since Luna will be wandering through the Hyades from sunset on, and several other occultations will take place (including at least one possible graze of the mag 7 SAO 93981 at around 9:20 pm).

Further, it's one of those wonderful just-past-first quarter nights that are starting to be very good about this time of year; the declination will max out at around +16 degrees a bit after 8 pm. That means with any kind of seeing you'll have steady views of some spectacular sights to keep you from getting bored between timings.

In fact, it's a good idea to keep an eye out after first quarter for quite a few months -- this isn't as high as this moon will get (highest point is just about at full this month) but it will be up there pretty well, which means much better detail is available.

Plato will be well placed for "crater counting" if the seeing is good.

Sinus Iridum will be just starting to come into the light -- if you're lucky you'll get to see it "hanging off" into space about the time of the Aldebaran occultation. It's at times like this that we understand why it's called the "Bay of Rainbows."

Above all, it's Copernicus night. The entire crater will be at almost ideal light when the moon is at its highest, making this the perfect time to contemplate the incredible collection of impact crater chains, visible in almost any scope when the sky is even moderately steady. This massive impact site also offers domes, cracks, rays, and just about any other feature you can hope for on the moon.

A little further south, plan on visiting Fra Mauro, Bonpland and Perry (they make a sort of "Mickey Mouse" not too far from the terminator) for the wonderful rille complex that riddles the entire area.

As the light crosses Palus Epidemarium, you'll also get to trace the obvious Rima Hesiodus. Late in the morning, or the next night, revisit this area and you'll get a look at one of the best "Rillevilles": the Palus also has the Rimae Ramsden, a striking crosshatch filigree that I have seen quite clearly in even my 4.5-inch newt.

Last but not least, the monstrous Clavius will be perfectly illuminated. Be sure to drop down to see the exquisite arc of craters inside; they increase in size with a perfection that somehow seems too unlikely to actually exist.

Overall, I'd have to say this will be a night to remember if the sky cooperates at all.

A couple of interesting notes about the 28th: first, the somewhat difficult Rima Sharp will be ideally placed from early evening on; it's near Mairan in Sinus Roris. This will be one of the best nights of the year to try for this elusive target.

Also, the terminator will be creeping across the Aristarchus plateau, making this an exceptional time to check out the remarkable Schroter's Valley. For the masochistic, Rima Marius will be right on the terminator and possibly showing well; don't count on it being dark, though. Sometimes it actually shows as a bright line! You may even get a glimpse of the Rima Suess a bit further south.

Of course, all of Mare Humorum will be lit, and the collection of rilles and fascinating craters in this area is probably the best on the moon: it's difficult to understand why this area is so neglected.

The next night, most of the curious Rima Sirsalis will be extremely favorable. For those who are interested in lunar geology, Sirsalis is a standout: most rilles are near the edge of maria, or in them. This one cuts across highlands almost exclusively, and seems to go in places where such a formation would be impossible. It offers a great deal of fascinating speculation as "the exception that disproves the rule."


Dave North; last updated: 1998 Dec 16 Prev Next