Monday, August 20, 2018

Don't Hate the Moon!

Some years back, a fellow HAL member (who shall remain nameless - he knows who he is) quite calmly stated at a Carrs Mill impromptu star party, "You know, if I could shoot down the Moon, I would." It brought to mind the old Looney Tune character, Marvin the Martian, who was always saying, "I'm going to blow up the Earth! It obstructs my view of Venus."

And yes, truth be told, the Moon does "obstruct" our view of deep sky objects - especially the fainter ones. In some ways, it's the ultimate in light pollution. All those moonlight sonatas and syrupy old love songs about walking in the moonlight... "Bah, humbug!" is the reaction of all too many amateur astronomers. I especially hear this reaction when one of our all-too-rare clear nights coincides with a full or near-full Moon. (There almost seems to be an inverse correlation between how much Moon is up there and the percentage of cloud cover.)

But, please. Let's not throw out the baby with the bathwater. In and of itself, the Moon is one of the most rewarding objects up there to observe (see my postings on this subject from Nov. 30th and Dec. 2nd, 1017, entitled "Explorers!").

Now this very upcoming weekend is a case in point. It appears that we're going to be presented by the weather gods with at least 5 clear nights in a row (Wednesday through Sunday), with a Full Moon on Saturday. So you have a choice. You can either stay indoors and mope, crossing your fingers that the skies will be clear for the next New Moon, or you can use this opportunity to take a look at some sadly overlooked lunar features over on the seldom observed "left side" of the Moon's Earth-facing hemisphere. They are far too many to list outside of a textbook, but allow me to highlight 1 or 2 per evening.

The crater Aristarchus and surrounding terrain, as seen by Apollo 15 astronauts

Wednesday: The brilliant crater Aristarchus (brightest spot on the nearside hemisphere) will just be coming into view, around about 10 o'clock (2 o'clock in a mirror-imaged view). If you're patient enough, you can actually watch the endlessly fascinating surrounding terrain emerge into the sunlight, as dawn sweeps over it over the course of the evening.


Meanwhile, down in the southern hemisphere, the dramatically misshapen crater Schiller is close to the terminator. This bizarre feature was created by a object striking the Moon at an extreme angle - almost missing it altogether.

Thursday: Go back once more to Aristarchus. The entire region will be in sunlight by this time, and the crater itself will be almost too bright to look at.

The Marius Hills, as imaged by the Lunar Reconnaissance Orbiter
(Click on image to see full resolution.)

Further south at approximately 9 o'clock (3 o'clock in a mirror-imaged view) and not far from the terminator, you'll come upon one of my personal favorite areas of the Moon to observe - the Marius Hills. This is a region of literally hundreds of volcanic domes and related features such as collapsed lava tubes. I remember well the first time I laid eyes on this feature, not knowing what I was looking at. Through the 80mm scope I was then using, it appeared that the Moon had either a bad case of acne or else goosebumps! The low elevation domes naturally show up best when they're smack on the terminator. They rapidly fade into invisibility as the shadows disappear just hours after dawn. So take a look while you have the chance!

Reiner Gamma, as imaged by Lunar Orbiter 4

Friday: For lovers of mystery and enigma, the Moon on Friday presents Reiner Gamma, one of the strangest features anywhere on its surface. Astronomers still do not completely understand how this feature originated, but they have some pretty good guesses. First of all, it is not a topographic feature. If you were standing right on top of it, you'd never know it was there. There is not an inch of elevation difference between its light and dark swirls, it being entirely an albedo feature. But orbiting lunar probes have detected a powerful, localized magnetic field directly under Reiner Gamma. It is believed that this field has charged fine dust particles in the regolith with static electricity, which has caused them to line up like iron filings around a magnet, like we used to do in high school science classes. (Do they still do that?) Reiner Gamma is found to the southwest of the Marius Hills.

No one knows why the magnetic field is there, making Reiner Gamma all the more intriguing.

Mare Orientale, as imaged by Lunar Orbiter 4

Saturday: To top things off, if you look over at the lunar horizon at about 8 o'clock (4 o'clock if your scope gives you a mirror-imaged view) you can catch a glimpse of the edge of what is possibly the most spectacular feature on the entire surface of the Moon, both near and far sides - the Mare Orientale. This is a truly gigantic impact basin (nearly 600 miles in diameter) although from the Earth we can only see its extreme eastern parts. Sometimes, you just have to take what you can get!

No comments:

Post a Comment