SJAA

Ephemeris

Mooning

David North


This month is special to deep sky folks: it has no full moon. Yet the two months adjacent both have two! This only happens every nineteen years, so enjoy.

Nevertheless, February is one of the "great" moon months. Why? Due to its inclined orbit, the Moon will be highest in the sky at the times of best viewing -- in this case on the 25th, when we will be a few days after first quarter.

But the days surrounding this "ideal" day will be very good indeed, with the Moon seemingly almost straight overhead. Needless to say, under those circumstances we have the best chance of outstanding steadiness, and this should not be missed. Even people who normally ignore the Moon might want to pay attention this time of year... besides, it's something the whole family can do from the comfort of the back yard.

The days before the 25th are perhaps my favorites. On the 22nd, the Hyginus and Triesnecker rilles will be front and center in virtually ideal light.

There is probably no more striking area on the Moon for looking at rimae: Hyginus is easy in almost any scope, and most will show the tiny chain of craters inside the rille itself! If you haven't hunted this down, it's a must.

Triesnecker, on the other hand, is a very fine complex and is sometimes elusive due to seeing or aperture, but most scopes will dig it out. It's crosshatched and complicated, and a great deal of fun to trace out if you have the patience.

A perennial favorite, The Straight Wall, will also be just about ideal tonight. Can you see nearby Rima Birt? What does it remind you of?

On the 23rd, the Apennine mountains really start to open up, and they are a spectacular view in themselves. But just inside them, toward the crater Archimedes, a very fine complex of rilles can be spotted. They are named Hadley and Bradley, after nearby peaks, and are the only area of rilles to be inspected by the Apollo astronauts.

The crater Plato shows well that night, up in the Alpine Mountains. It's something of a challenge to spot the five major craterlets in the dark, smooth floor. The nearby Alpine Valley may give you a glimpse of it's central rille, a very hard target. It was showing the previous night, but I've had more luck with slightly raised illumination such as this night will offer. However, trying even tomorrow night may give good results, and this is always a feather in one's cap.

The 24th is showtime, big time. Copernicus will be just about ideal, and there is nothing else on the Moon like it, especially seen high in the sky. It's surrounded by an incredible field of secondary craterlets, tiny dots that form lines and patterns all around. The crater itself has one of the best forms seen on the Moon, and you can normally pick out the collapsing terraces on the walls. The several central peaks are also clearly defined.

In the general area around the crater you can find all manner of domes, rilles and other lunar features too numerous to mention. If you haven't hunted this area, tonight's probably the best theoretical night of the year.

Also, this should be one of those nights where Sinus Iridum is "hanging off on the dark side." It will be only partially illuminated, and the massive walls will extend into the darkness. This is easily seen in any scope, and gives you a good idea why this area was named the "Bay Of Rainbows." Watch it emerge as the evening goes by... things really do change on the Moon!

Then comes the highest elevation of the month, on the 25th.

The main area of concentration should be Palus Epidemarium, the Marsh of Diseases. The entire floor of this southern area is cracked with rilles, and you should still be able to trace most of Rima Hesiodus crashing through the mountains to join the complexes inside. It's what I call "rilleville," and when it's showing well it's one of the most memorable areas for any scope. I've managed to nail everything in and around it in a 4.5-inch newt with a great deal of patience, so don't be dismayed if you don't see anything at first. Hang with it.

If that's not enough for you, travel a bit north to Mare Humorum, another extremely rich area. Later in the evening the light will be getting very good on Gassendi, which is a marvelously complicated nearly sunken crater (say that five times fast). But the incredible arcing Rimae Hippalus, extending from the southern rim of Humorum, should be well seen all night.

The next night, revisit the western edges of Mare Humorum. You'll be surprised how much can be found in the way of interesting rilles, craterlets and other features. This entire area of the Moon is far more rich than its better known eastern complements, but for some reason is largely ignored by most amateurs.

There are several "close approach" events during the month (Moon near this planet or that star) but none of them outstanding. Further, most librations this month show very little promise of any particularly interesting views of the "far side."

This simplifies things a little: it means we can concentrate mostly on "normal" observing and reserve the "special events" for later in the year.


Dave North; last updated: 1999 Jan 18 Prev Next