The Moon
1998 Mar 3
For once the sky was clear.
Though a bit wobbly, it supported 300x with profit. Observations
were done with a C8 at 300x and a 4.5-inch newt at 180x. Contrast was
very good. I'll travel around by Rukl Atlas page for the convenience of
anyone wanting to "sing along at home."
Rukl Page 14
The first thing to catch my eye was the Rimae Burg -- all the main
tendrils were visible with some patience, particularly the main one
running from the mountains through the north of Lacus Mortis (the Lake
Of Death! wooo...) past the crater of the same name. One "vertical"
stretch near the curious ridge running north of the crater looked very
much as if it were made up of a series of small craters. In the right
light, all this is a pretty easy target.
The less well-defined craters Mason and Plana offered up the tiny
detail inside them (small craters and a central peak in Plana). They are
exaggerated by the smoothing caused by partial filling with mare
material. Again, the right light is critical to appreciating this.
Rimae Danielli were doing a fan dance. Sometimes I could hardly see
the complex, and other times it seemed to sit still in the eyepiece and
I'd wonder how it could be difficult at all. The main branching was
delicate but definitely visible in full, and there may have been an
additional minor branching (but I'm unconvinced). It was almost as
inspiring as Triesnecker at its best.
Of course, when in this area, there's Poseidonius. And it was
extremely gratifying to get a look at it, since it seems I've been
unlucky at this point in every lunation for nearly a year. Against all
odds, tonight the whole fat fig was splattered all over my eyepiece with
all the rilles and collapses and little craters you could ever ask for.
It was particularly well lit to see the subtle height differences in the
remaining walls, and at times I was able to see ten significant segments
of rille. A really wonderful look at one of the best spots on the moon.
The rilles in Atlas were also easy, and well worth a little time.
In poor seeing, it simply looks like a nice, largish crater, but when
you can steal a look, you really get a feel for the tremendous tectonic
stresses that came into play. Some collapses and minor cratering were
also notable in Hercules.
Rukl Page 24
The Serpentine Ridge (now inaptly named Dorsa Smirnov) was just on
"this" side of the terminator, giving it ideal relief. It's easy for any
small scope, but amazing no matter what aperture you bring to the
party...
If you run along the Dorsa to the south end, you come to Plinius
and the terminus of a major rille structure (the rimae Plinius, of
course, which extend the Rimae Menelaus... part of a major classic rille
structure around the rim of Serenitatis). Three major branches could be
easily seen, and they seemed to submarine just below the Serpentine
ridge, then reappear slightly beyond a minor dorsa above Dawes.
In the same area is a remarkable dark albedo zone (really an
extension of the darkness that edges all of Mare Serenitatis). But this
particular spot has exceptional contrast as well as very hard edges; the
color change is strikingly sudden.
Rukl Page 25
For some reason, Romer (Rukl 25) was particularly attention-grabbing
tonight, partly because some trick of the light made the edges
practically fluorescent, and partly because the central mound and
internal crater were very nicely lit for exquisite detail.
Traces of the rimae Littrow were somewhat visible in the early
evening, but got more difficult as the night progressed and seeing
slowly deteriorated (and the moon moved lower).
Rukl Page 35
Wandering a bit south of Plinius we arrive at a pair of domes (Arago
Alpha and Beta) that were in perfect light; one of the best dome
sightings I've had other than Rumker. The mounding seemed exceptionally
steep on Alpha, and the central crater was obvious. Beta was
considerably more subdued, but also further from the terminator. It's
very possible it's also quite a sight when equally well-placed.
Further south in Mare Tranquilitatis is an incredibly complex,
nearly radial structure of dorsa centering on a "dorsal ghost" named
Lamont. It's an amazing view in this kind of light when both color and
shadow contrast are at their best; ridges spider in all directions and
as they turn in the light, the play of different patterns is
captivating. It's not necessary to point it out or look for it -- the
feature will grab you by the throat if you ever get lucky and catch this
kind of view.
Rukl Page 36
I also got one of my best ever views of Rima Jansen (Rukl 36), a
delightful little sinuous rille that seems to end in a small crater.
There also appeared to be a much smaller rille nearby. The structure is
highly reminiscent of the more well known Rima Birt near the straight
wall, but the sinuous nature seems more pronounced and squiggly. A
nearby tiny section of rille, closer to the naming crater, was
fleetingly visible but not commonly charted; you might try looking for
it sometime.
Rukl Page 46
The timing was just right for my observing partner to spot a very
pronounced ray in the crater Hypatia (the "heart" of the moon due to its
odd shape). The rimae Hypatia were also surprisingly easy, as they have
been elusive most of the preceeding year. They run along the edge of the
indentation between Serenitatis and Sinus Asperitatis, just north of the
crater after which they are named. They peter out into this mare zone
with an increasingly narrow fork that's jammed into a small range of
hills just off the peninsula. It's tempting to think there is some
selenological relationship, but I'll be danged if I know what it is.
Rukl Page 57
The Altai Scarp (now officially Rupes Altai, which somehow makes me
think of "overpriced in Bangladesh") was right on the terminator, in
fact a little in shadow at its westernmost. At such a time it shows
clearly as the "shock ring" it is -- a rumpling caused by the impact
that formed Mare Nectaris. For anyone who has ever hunted down Mare
Orientale in a favorable libration at full moon, the resemblance will be
obvious save for one thing: on Nectaris, we can get a clear, nearly
overhead view of the same effect.
This was actually one of my own first "theoretical" observations
(only a hundred years or so too late to be cutting edge...)
Rukl Page 67
Last on the list for the night was the larger Janssen, a ruined
structure in the southern wastelands. Even at first glance, the massive
Rimae Janssen were visible in the 4.5-inch. They seem to form a partial
inner ring that is filled out by the walls of the larger structure. I
have always assumed (without knowing) that this is a slumping ridge
where another larger crater collapsed under the present Janssen.
Overall, it's one of the easiest massive structures when it comes to
seeing the hexagonal shape such massive walled plains often assume. As
the lunation goes by, Janssen rapidly disappears, it's ruined walls are
so low in our epoch. This is one of those places everyone should visit;
the level of detail is such that the most modest to the very best scopes
will pay off handsomely.
Dave North;
1998 Mar 4