Telescope Reviews: Help with Orientale

Carol -

I think Preston is referring to the May 2008 column "Hide-and-Seek Basin" by Charles Wood, which is illustrated (on p. 64) by LPOD photos of Mare Orientale from George Tarsoudis and Paolo Lazzarotti. On those, the "Outer Rook" Mountains are labeled as you indicate -- between Lacus Autumni and Lacus Veris -- while the "Inner Rook" Mountains are labeled on the limb. The IAU name Montes Rook has a long and complicated history, and it was even dropped for a few years. It was reinstated in 1964 when rectified Earth-based images made it appear that Orientale had two main rings -- the name Montes Rook being assigned to the inner one. But Lunar Orbiter views soon made it apparent that there were at least two inner rings, and hence the names "Inner" and "Outer" have been in informal use for at least 30 years.

The following image (using LO-IV-187M as a background) illustrates where the limb lines would have been at the time of your June 26, 2008 observation at 07:30 UT compared to where it was at the time of Paolo's image (Jan. 1, 2005 at 02:25 UT) and also an LPOD Photo Gallery image by Howard Eskildsen in which the part taken at 11:45 UT on that same day would have almost exactly matched your view.

If Preston was looking just before sunrise he might have seen Orientale very slightly farther onto the disk than in any of these.

Although the lighting in the Lunar Orbiter view is quite different from these high Sun views, if you use the pattern of the dark mare as a guide, and the limb lines for orientation, it's possible, with a little effort, to correlate the things recorded in the Earth-based photos (where the mare are seen with extreme foreshortening) to the corresponding features in the LO view. The Inner Rook ring is actually seen from Earth in at least four places: in the foreground (where it is seen just beyond the dark ribbon of Lacus Veris), to the north where it crosses over the limb line, and then again to the south where it comes back to the limb line, and possibly in between where some of the highest mountain tops may be visible as a thin bright line on the horizon.

Judging from Howard's photo, the "bright white line similar to the Apennines under high sun angles" that Preston saw may have been the Earthward-side of the Inner Rook ring (just beyond Lacus Veris, especially bright to the left of where "Inner" is printed under "Orientale" in the LPOD mouse-overs). As the LPOD labels indicate, the ellipse of the Inner Rooks curves back around to the right becoming visible on the limb at a point a little to the right of where "Inner Rook" is printed in the sky. A bit of the Outer Rooks is also visible on the limb just to the north of these (under the "Outer Rook" LPOD mouse-over label). The Cordillera ring seems quite difficult to see under a high sun, although in Howard's photo it produces a distinct step on the limb (beyond Schlüter).

The most prominent limb peak in Paolo's LPOD image (the one to the left of the "Inner Rook" in the LPOD sky -- or by following the "Lacus Veris" arrow in Howard's image) actually seems to me to correspond to the elevated region just above Maunder in the Lunar Orbiter view shown here. This, like Kopff, is right on the edge of the Mare proper, and is well inside what I believe is generally taken to be the "Inner Rook" ring. The Inner Rooks themselves are not really visible at this point on the limb: they are well beyond the limb and hidden by foreground elevations like this.

-- Jim

Edit: reference feature identifications on LPOD image to mouse-over labels -- the titles previously used move depending on the window size

Edited by Jim Mosher (06/28/08 11:26 PM)