Moon: 5/11/2008

Marek Cichanski

I just got in from a very pleasant little Moon session, and I thought I'd write up a quick OR. I didn't take any written notes, this is just a quick and dirty OR from memory, looking at Rukl as I write...

This was my first real Moon session with the "Montebello Special", the 10" f/5 dob built around the old primary mirror from my 2002-era XT10. It has a 2.14" secondary, a bit smaller that the original one IIRC, and uses exclusively 1.25" eyepieces. For tonight's session I mostly used the 13mm type 6 Nagler, for a magnification of 96x. Towards the end of the session I popped in the 7mm type 6 Nagler, for a magnification of 179x.

Seeing wasn't anything to write home about, commonly only 2 out of 5 by my judgement, with reasonably frequent intervals of 3, and very rare moments of 3.5 or 4. Still, it was useable, with a little patience.

The near-perfect first quarter phase made the maria Serenitatis and Nectaris the stars of the show tonight. The color contrasts between the lavas in Serenitatis were very prominent. Perhaps I should say 'albedo contrasts', since both of the lava types look grey, but I can't help thinking of the recent spate of 'saturation-enhanced' images taken by amateurs. A nice example can be seen on Russ Croman's site, for example:

http://www.rc-astro.com/photo/id1018.html

There's another nice example on Chuck Wood's LPOD site:

http://www.lpod.org/?p=529

According to Wood's "The Modern Moon" (your one-stop shopping place for actual lunar geology, as opposed to quasi-scientific 'selenology'), the color contrast in Serenitatis is due to differences in composition between lavas of various ages. Most of the darker material forming the southeastern 'rim' of the mare is a bluish, high-titanium basalt sampled by Apollo 17 and dated at around 3.8 to 3.7 Ga. The youngest basalt in the central basin is thought, from crater counts, to be around 3.4 to 3.0 Ga. As Chuck Wood puts it, "Thus, the lava-filling history of this lunar basin lasted 700 to 800 million years, a span of time that is immense by the standards of terrestrial geology."

Immense it is... this 700+ million year history is considerably longer than the entire Phanerozoic Eon, for example. In other words, it's a span of time that is pretty well equal in duration to the entire history of multicellular life on Earth, and predates that history by billions of years. As Arthur C. Clarke put it in "2001": "Here was age inconceivable, but not death, for the Moon had never lived... until now".

I really get a kick out of how much great mind candy there is on the Moon, and how it can be inspired by something as simple as the color contrast in Serenitatis.

A funny thing just occurred to me - I've enjoyed looking at 'presolar' quasars, whose light predates the origin of the solar system, and is thus older than any rock I'll ever see. Some quasars, however, are definitely not 'presolar', such as the famous 3C273 in Virgo. The discovery of the redshift in the spectral lines of 3C273 opened the door onto a whole new world of cosmology, once it was realized that this object is ca. 2 billion light-years distant. But here in Mare Serenitatis, we can look at a story written in rock, and it's older than the much-vaunted light from 3C273. I get a kick out of that, too.

An interesting part of the terminator tonight was the region shown in Rukl map 34. I saw what looked like a steep-sided plateau between Godin B and the crater Lade (shown on Rukl 45). It seemed quite distinct and real, but Rukl shows no plateau there. It was a powerful illusion of an elevated plateau, even though it was just a low-lying area bordered by some funny shadow effects. Curiously enough, there really IS an "interesting plateau" (Rukl's words) to the west of Godin. That area was still largely in shadow, though, and I didn't see the plateau.

The Rima Ariadeus showed up reasonably well, as did the eastern end of the Hyginus rille.

The real star of tonight's show, though, was the libration zone along the eastern limb of the Moon. I don't have the exact information on tonight's libration, but I'd just about be willing to bet that the eastern limb was rather heavily librated towards us. I could see the terra material on the far side of Mare Smythii quite distinctly, for example. Ditto for Mare Humboltianum. The crater Neper showed up very nicely as a prominent albedo feature between Marginis and Smythii, with its central-peak complex standing out nicely against the lava-flooded floor. I could also see the crater Goddard on the northeastern edge of Marginis, and I'm reasonably confident that I could also pick out Hubble. Some cliffy topography that was silhouetted against the black sky beyond the limb might have been part of the large crater Joliot. All in all, it was a really neat view of the eastern libration zone. It's always a thrill to 'see the far side of the Moon'.

The seeing wasn't generally good enough to justify going beyond the 13mm Nagler, but I eventually tried the 7mm Nagler, just for grins. and even though the seeing was mostly funky, it certainly produced some grins! Until I built this scope, I had mostly used my 6" f/10 Mak-Cass, which has roughly the same focal length as the Newtonian that I was using tonight. With eyepieces like the 7mm Nagler, the view through the Mak-Cass was often quite nice, but it was a bit dim, and was near the scope's diffraction limits. But with 10" of aperture, the Moon looked considerably brighter and sharper. I can't wait to get my equatorial platform up and running again, and to have a night of good seeing. I have a feeling that the 10" will provide some more memorable Moon sessions.

All in all, a pleasant little spring evening with the Moon.

Oh, and if you haven't seen the high-def video from Kaguya yet:

http://www.planetary.org/blog/article/00001421/

Marek