I enjoy that area closer in, especially the smeary Julius Caesar (messed around good by the "Imbrium Event" -- I kinda like the understatement of these terms).
CCD image by Bill O'Connell using an 8" SCT.
Sinuous rilles may be the remains of long-ago lava tubes, perhaps once roofed, where the thin lunar lava once cut a path. Other rilles, like Ariadaeus, may be grabens, where the surface has dropped between two faults. Still others, especially around the edges of the maria, may be cracks caused by isostatic "settling" of the maria. Rima Hyginus doesn't clearly fit any of these patterns. It often appears like a crater chain in the telescope, but lunar photogeologists say the "craters" are collapse pits, where the wall of the rille has fallen in. The crater midway along the rille is a true crater.
Many portions of the lunar surface show forth hidden treasures for those who look a little longer, and the Hyginus area is no exception. Under low lighting conditions, a very odd spiral feature is visible, as described below in a passage from Wilkins & Moore's classic book, The Moon:
North of Hyginus and connected by a wide but shallow valley is a curious spiral mountain (Schneckenberg). This has broad low walls and the interior is depressed only about 700 feet. Schmidt and Goodacre drew a central craterlet, but Brenner and Fauth many more. Wilkins found two craterlets and a hill on the interior, all difficult objects. Krieger, in his Mond Atlas, Vol. I, Pl. 8, depicts the interior as filled with shadow except for a central strip, on which is a pit. Anther drawing, under a higher angle of illumination, shows two pits, from the more northerly of which a branching cleft runs north-east. Krieger also found other delicate clefts, confirmed in part by Fauth and Klein."
(The Moon, Wilkins & Moore, Macmillan, 1961 (2nd Edition), Page 57)
Fortunately, the name "Mt. Schneckenberg" didn't stick (the feature has no IAU approved name), but the odd spiral mountain is still there.
This Apollo 10 oblique telephoto view of the lunar nearside
is centered on the crater Hyginus ...the crater is about 10
kilometers (6.5 statute miles) in diameter. From the crater
the prominent Hyginus Rille extends east-southeast toward
the camera and northwest toward the Sea of Vapors. The rille
is about 3 kilometer (2 statute miles) wide and more than 200
kilometers (130 statute miles) long.
(NASA Photo ID: AS10-31-4650 File Name: 10075150.jpg
Film Type: 70mm Date Taken: 05/18/69)
Look for Hyginus at first quarter, or just before last quarter.
There are quite a few elongated blobs of stuff in that area, most commonly theorized to be huge ejecta deposits from the Mare Imbrium Event (or Big Honking Smash). To me, that zone looks like someone smeared it with a pallette knife, or like wall texturing...
Nevertheless, out come the books, riffle riffle. In Rukl (page 34),
nothing there. But in the Times Atlas, I hit paydirt. There's a broken catena
of craters, mostly of two sizes (small and smaller) running in exactly that
position, as yet unnamed. Very striking in this exact light -- another one of
those things that make you wonder why you haven't seen it before. Of course,
it's a question of a lot of things: exact light angles, steadiness,
|Chart 33||Moon-Lite Atlas for chart 34||Chart 35|