Hitchhiker's Guide to Rukl Chart 18

Aristarchus and Rimae Aristarchus (JRF <freeman _at_ netcom.com>)

Bright crater Aristarchus is visible to the naked eye as an albedo feature when it is well illuminated. A system of rilles starts north of it, and extends to the north.

3/9/98: Schroter's Valley was just barely all in sunlight -- the region between the Cobra Head and Herodotus was still darkly shadowed by nearby high terrain. I could see Rimae Aristarchus, and associated rilles I, III, and VI. Rille III was most prominent northwest of Prinz -- I could not see any of III, IV, or V where they lie parallel, close to 27 N 46 W.

Aristarchus (ALPO)

ALPO has a Selected Areas Program page on Aristarchus.

Schroter's Valley (JRF <freeman _at_ netcom.com>)

Schroter's Valley (Vallis Schroteri) starts northward slightly north of crater Herodotus, then bends through nearly 180 degrees to the east before opening out onto Oceanus Procellarum. I have seen it well in as little as 55 mm aperture.

Schroter's Valley (Akkana)

A horseshoe-shaped, sharp-edged canyon which seems to pass underground as it exits Herodotus, then emerges onto the surface and fans out as it makes its 180-degree bend.

Schroter's Valley does not begin to be visible until the area where it lies is well past the terminator. Just before sunrise on the valley itself, Rupes toscanelli is obvious, but look for a small but prominent trough which bisects a small hill north of R. toscanelli. The trough is unnamed on Rukl, but is drawn just over the "50 W" on chart 18.

Schroter's Valley (David North <d _at_ timocharis.com>)

Schroter's Valley (Vallis Schroteri in the bogus latinate hokum the official bodies have incorporated) "begins" in a highland, as does it's smaller twin, Rima Birt. Since the valley looks like a snake, the elongate depression where it begins was nicknamed the "Cobra Head" for reasons obvious to anyone observing it in reasonable seeing.

Current theory states that the entire valley, including the head, are a collapsed lava tube -- a course lava found from the "Cobra Head" through the highlands and to its eventual terminus near the lowland mare material. After the lava drained, it is presumed the tube collapsed from the weight of the material above, leaving the trench as we see it. The "head" was formed due to a larger collapse into the chimney from which the lava emerged from a deeper source.

Such selenographic processes are not yet well enough understood to say with any certainty if that is indeed the process that took place, or from what level the lava originally began to rise. The curious nature of the "island" in which Schroter's Valley is found adds further fuel to the speculative fires; it's a curious area of isolated highland in the midst of large maria.

Rima Marius (JRF <freeman _at_ netcom.com>)

This narrow sinuous rille wends across Oceanus Procellarum south of Aristarchus and Herodotus.

Rima Marius (David North <d _at_ timocharis.com>)

... out of the corner of my eye, I spotted a filigree of light on old Procellarum -- a faint wisp, a hint of a line. Very intriguing. So I hunted the area, patiently, and slowly but surely a story unfolded, an image of light rather than darkness... it was Rima Marius! This feature is, at least to me, very elusive. But for the first time I recall, I was tracing out almost the entire length, but illuminated! It was a *bright* line on the darker floor; already the sun was reflecting from the interior side of this shallow trench rather than casting a shadow from its lip.

Possibly the interior matter is considerably brighter than the surrounding mare material; I don't know. That would explain the extraordinary contrast, and there's some small reason to believe the underlying material in that area could be intrinsically bright, with Aristarchus so nearby. But that would also imply a certain degree of youth -- unlikely in my understanding that rimae are largely old features. On the other hand, after forming there is some collapse of the sides of the walls, and perhaps some of this "mass wasting" took place relatively recently..? Jarred loose by the impact that formed Aristarchus?

And there was a lesson for me: just because the mapmaker draws it dark doesn't mean it will be when you see it. I should know better by now having seen this kind of thing before, but I don't. Ah, well.

The rille itself is a prototype "sinuous," bending throught three distinct arcs somewhat reminiscent of the profile of a face from the bridge of the nose to the chin. Most of this showed well in the telescope, save the thinnest part of the end, which eluded me (the rille goes a bit further past Marius B than I noted). It's graceful shape outlined against the dark floor was very attractive of itself, even without the excitement of the hunt. This was clearly the best sighting I've ever had of it, and I have to say it's much more appealing when the majority of it is visible -- rather than hunting little bits and dabs in shakier seeing or poorer light.