8 replies to this topic

[Jeremy Perez]

I've been looking forward to making this observation for a while. The early morning of August 27th offered a great view. Lighting was the opposite of most photos and sketches I've seen, so later comparisons have been a little difficult. The observation was made with a 6" f/8 Newtonian, a 10 mm Sirius Plössl and 2X barlow for a magnification of 240X. (No filter.)

The near-perfect fractalish arc of craters across the face of this 225 km wide crater was incredible. I was surprised to find that a crater in the southern wall (Clavius K) continued the arc very nicely. As old as this crater apparently is (4 billion year old Nectarian period), its floor and overall structure seem surprisingly crisp and well preserved. It's truly beautiful. In the light of the setting sun, the crater floor displayed a smoothly shaded vignette getting darker from west to east.

If the ages of the main arc of craterlets weren't so varied, I could well imagine a comet or loosely bound asteroid passing uncomfortablly close to earth, and getting it's path deformed for an impending collision with the moon. As it passed a few hundred miles above the atmosphere, tidal forces pulled it apart, while it's existing rotation splayed the pieces out in a gradually expanding arc that ceased expanding an hour and a half later when it plowed into the Clavius basin. But I had to dump that theory after some limited research blew it out of the water.

As I raced against the clock...and a deepening fatigue to complete the sketch, I noticed a couple interesting features. Some ravines ran north from Rutherfurd Crater. It was hard to tell how these formed--whether they are stress fractures or thick ejecta streamers from the Rutherfurd impact, but Grego's Moon Observer's Guide refers to them as radial impact ridges. I also noticed that Clavius-CB seemed to rest atop a low dome.

A number of very small craters sprinkled the floor, and I tried to plot most of the readily visible ones. Not counting Ruthurfurd and Porter (Clavius B), I marked 32 craterlets on the floor of Clavius. The smallest, just east of Clavius-N, was 3 km in diameter (2 miles), based on this lunar chart. According to Grego, a 200 mm scope will reveal up to 30 craters on the floor. I'd say that number should be bumped up a bit, since seeing that night wasn't too great to begin with--hovering around Ant. III--and I'm only using a 150 mm scope. How many craters have you counted on the floor?

The sketch, rollover labels, and observation notes can be found here.

[photonovore]

I can tell you're a graphic artist! Nice report and graphics!!

Rutherfurd is an interesting crater, isn't it? Altho Wood simply says "who knows?" about those radial features, other authorities observe that this crater possesses many of the hallmarks it would be expected to have (Schultz, Wilhelms) if it were formed from a somewhat oblique impact from the SSW; it is not round but slightly oblong in a N-S axis, the central peak is offset to the NNE, the ejecta blanket (as seen on LO IV-130-H3) also drapes heavily around the northern rim and the ridges/gullys are radial to the NNE as well-- Rutherfurd even has faint rays accompanying the radial features, reminiscent but less defined than those of, for example, Messier A-- and it's a Copernican period crater as well, according to Wilhelms (not that that has anything to do with an oblique impact but goes a long ways towards explaining it's continued possession of such discreet features.)

I'm not suprised at your high crater count in Clavius--you certainly have a good scope design for the Moon-- and I share your opinion that the resolution limits we see touted in the popular guidebooks are pretty conservative as well.

Thanks for sharing!

[kraterkid]

A wonderful report and a excellent sketch Jeremy! Clavius seems to be briming with craterlets and floor detail in your drawing, you are definitely a keen observer and your sketch reflects that perfectly. I love the rollover labels, how difficult is this to do? I never label my sketches and would find this method a great way to indicate nomenclature.

Fantastic work,
Rich

[desertstars]

Wow, an Arizona observer able to view the Moon in August? That's an amazing feat all by itself! (Yes, it was clear statewide that night, and I was out when the Moon rose, but our conditions near Tucson were Ant. IV - at times V! )

My best craterlet count in Clavius so far has been 29. It would seem I need to take a much longer look. (Any excuse will do! )

Excellent report!

[dgs©]

Clavius is my most favoritest spot on the moon. Sometimes, when things are clear, and seeing is good, I believe I'm seeing debris (boulder-like objects) scattered in there as well. Could be my imagination though.
Certainly more detail in there than I have bothered to count yet. Maybe a micro cassette recorder would be good for taking notes at the eyepiece, for later dissertation.

I always marvel at the cosmic accident that left that arc of decreasing diameter craters. Knowing the age differences makes the odds of such a phenomenon even more remote... astronomical odds, even.

Nice work, as usual, Jeremy.

[LivingNDixie]

Nice report!

[Jeremy Perez]

Thanks you guys!

Man, Photonvore, that's some great info. My web hunting skills for that sort of info hasn't been so hot. I need to increase my meatspace library.

Rich, the path to rollovers was a river of tears for me. Most of it was due to my limited powers of web scripting. But I eventually beat it down. You need to have a script in the header of any page that uses rollovers to 'prep' the page. Then you have another script for each rollover. I've set up my weblog templates to keep the rollover script in every page header so I'm don't have to worry about that. Then I copy and paste a template script into the body of the page wherever I need it. There are 5 lines in the script that need to be customized each time, to point to the default image, the rollover image, and then some 'names' you give to the rollover. It's weird. I can email it to you. Or heck, I could post it somewhere...I wonder, would the sketching forum, or the software forum be better?

Tom, it's been really frustrating with the evening clouds. Maybe I should say 'tantalizing'. You know, how the storms clear out around sunset, and the sky gets huge clear regions (seeing stinks, but oh well), and so you drag the scope out. But then as soon as you're all polar aligned and the scope is cooled down, this hours-long encore of weird, flat, orthographic cloud waves moves in to dash your hopes to little, pointy smithereens. That super-hot desert evening turbulence must get aggravating for the high-fi views. The parallels with lunar observing vs. DSO observing are interesting--plotting the smallest crater you can spot vs. the faintest star you can discern / detecting some subtle hump or ripple on a crater floor vs. detecting some faint extension of nebulosity / figuring out which feature to start with vs. figuring out which feature to start with.

erm...

David, I can just hear my recordings now..."one ca-rater, two ca-rater, three ca-rater, four...five ca-rater, six ca-rater, seven ca-rater, more!" Actually, that would probably be really helpful with some of the transient features that mobile shadows mess with over the course of the observation. That way, when you are marking in the main features, but are worried about various smaller, disappearing sparkles of light scattered across your subject, you could call them out, and then finalize the sketch inside with some of the things you missed since the sketch began. I hear what you're saying about 'astronomical odds' of a crater arrangement like that. It seems astounding. I wonder what the statistical odds really are? Magnetism. Subterranean magnetism! That's gotta be it! And the Romulans, let's don't forget the Romulans.

Thanks again everyone for the comments and support.

[Carol L]

Another great report and sketch, Jeremy!
I never counted the craters before but it sounds like fun.

[dgs©]

Subterranean magnetism

That'd be Sublunar magnetism wouldn' it?

Yeah, Romulans. Or maybe even those dastardly Goauld. They tried an asteroid once if I remember rightly.