Hitchhiker's Guide to Rukl Chart 54

The Straight Wall (Thierry Legault)

Thierry Legault's CCD image of the Straight Wall at first quarter (left) and last quarter (right) Note the differences in scale, due to the variation of distance of the moon between apogee and perigee.

The Straight Wall (JRF <freeman _at_ netcom.com>)

This long north-south exposed fault face in eastern Mare Nubium faces west, so that it appears as a long dark streak of shadow just after dawn, a few days after first quarter, but is brightly lit at last quarter, just before its sun sets. The patch of hills near one end gives the entire feature rather the appearance of a sword -- the wall is the blade, the hills are the hilt.

Rupes Recta (Robin Casady)

Robin Casady's image of Rupes Recta.

Rupes Recta / The Straight Wall (David North <d _at_ timocharis.com>)

Rupes Recta is a slip fault, which not only looks like the san andreas, it is like the san andreas (unlike the common "spread" rilles like Hyginus).

The Straight Wall, Birt, Birt A, and Vallis Birt (Akkana)

When near the terminator, the Straight Wall stands out as a displaced source of shadow. In the shadow of the Straight Wall, the rims of craters Birt and smaller Birt A are prominent circles in stark black and white contrast.

Everyone's first reaction upon seeing this area at sunrise is, "What is that crater the Straight Wall is in?" But it isn't a named crater, and when the sun angle gets higher it doesn't look like a crater at all, just a semicircular set of wrinkle ridges in Mare Nubium. Presumably it was in fact a crater at some point, and the wrinkle ridges are all that's left of the west edge of the crater after the rest filled with mare material.

Opposite Birt from the Straight Wall, there's a slight valley paralleling the Wall which is unnamed in Rukl. A group of us proposed calling it "Vallis Birt".

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

Rima Birt does a fairly good Schroter's Valley imitation, but in fair seeing, it actually seems to extend beyond the mini cobra head. However, when the seeing really settles, you can tell it is just formations in the same line. I wonder if they are related?

Rima Birt

A TAC member who prefers to remain anonymous comments: "Rima Birt looks like something looking for an ovum. :-)" David North <d _at_ timocharis.com> adds, "It actually found the egg a few million years back. Take a close look..."

Hesiodus A (JRF <freeman _at_ netcom.com>)

Note the double concentric walls in this small crater.

Hesiodus Sunrise Ray (JRF <freeman _at_ netcom.com>)

Approximately as the sunrise terminator crosses the common wall of craters Hesiodus and Pitatus, the rising sun shines through a breach in that wall, and creates a ray of light that very nearly bisects the smaller crater. This apparition seems first to have been described in the article beginning on page 74 of the July, 1996 issue of Sky and Telescope. It has been seen several times since then, with apertures as small as 60 mm. For predictions for it, see the RLO web site.

See also the L'ALPA page on the Hesiodus ray (in Italian) for timing predictions.

The Beginning of the Hesiodus Ray (...Akkana)

I'd caught the Hesiodus ray several times, and had sketched it once (right).

But on 9/18/99 at Fremont Peak, watching the early sunrise over Clavius, I noticed nearby fully-lit Pitatus and fully-dark Hesiodus, and wondered whether I might finally have the chance to see the beginning of the Hesiodus Ray.

At about 9:35pm PDT, I thought perhaps I could see a glint of sunlight on the far wall of Hesiodus opposite Pitatus; but I couldn't be sure, though the little 80mm refractor. So I headed into the observatory to take a look through the 30". Unfortunately, there was a line, so it was 9:45 by the time I got my eye to the eyepiece -- but there was the embryonic Hesiodus Ray, clear as day. I hurried back to the 80mm to sketch it (right).

Hesiodus Ray CCD image (Robin Casady)

Akkana's note: Robin caught the only CCD image I've seen of the Hesiodus Ray, fairly late in its cycle.

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

This delicate rille starts near the western end of Hesiodus, extends across Rukl chart 53 and onto Rukl chart 63, where it ends in the middle of the Palus Epidemiarum. It appears to run through or under the mountains which form the eastern edge of Palus Epidemiarum. I have seen the entire length in a 90 mm refractor.

Rima Hesiodus (Randy Muller <71172.1234 _at_ compuserve.com>)

I immediately noticed a thin gash extending E-W for a surprisingly long distance.

The gash turned out to be Rima Hesiodus, stretching across 3 Rukl charts all the way from the crater Hesiodus (54), going UNDER (apparently) Rupes Mercator (a 'rupes' is a scarp), continuing through the Marsh of Epidemics (Rukl 63, Palus Epidemiarum; Yuck! Truly this is the 'bad' side of the moon, no serenity or tranquility here!) finally arriving just north of Capuanus. Rukl shows a nice system of rilles just west of this, but the sun had not yet risen on this area.

Rima Hesiodus was pretty straight for the most part, and it was quite amazing that it continued on both sides of Rupes Mercator. Rukl shows it continuing over this feature, but I did not see this.

Pitatus (JRF <freeman _at_ netcom.com>)

Flooded walled plain crossed by several rilles.

Pitatus Sunset Ray (JRF <freeman _at_ netcom.com>)

The same gap through which the Hesiodus sunrise ray shines may also emanate a sunset ray across the floor of Pitatus, but as of mid-May, 1997, no one seems to have seen it yet. For predictions for it, see the RLO web site.

Pitatus Sunset Ray (...Akkana)

Kopal's New Photographic Atlas of the Moon includes a photo (plate 78) from Pic du Midi showing sunset over Pitatus and Hesiodus. The photo does not show a sunset ray. Of course, this is not conclusive; if there is a ray, it might have occurred earlier than the time of the photo.

See also the L'ALPA page on the Pitatus ray (in Italian) for timing predictions.

The Lassell Stripe (...Akkana)

April 24, 1999 (UT 4/24/99 about 05:50): SJAA Houge Park star party: David North noticed a transient shadow near the Straight Wall which he'd never seen before, and neither had I. There's no hint whatsoever of this feature on Rukl's chart 54, and even the Times Atlas didn't seem to show it, though it showed a rille there, Rima Lassell, which at least went in the right direction.

A search through several other books and finally found a trio of drawings in Harold Hill's "A Portfolio of Lunar Drawings" which matched my sketch almost exactly; apparently it's a rare feature which is only visible when the light is just right. Hill thinks it's a fault scarp, but it's much less prominent than the Straight Wall.

I got another good look at the stripe, with a slightly later terminator, on 3/14/2000 at about 03:30UT.

Lassell D (David North <d _at_ timocharis.com>)

This is a tiny crater with a bright halo that makes a surprisingly white spot at first glance. I got my revenge, though, when the central crater in the talcum powder blotch was more easily visible in my dorky C8 than any of the refractors...

A note of humor was added when we looked it up subsequently in Rukl, only to discover his description was "looks like a white spot."

Duh...