Concentric Craters (Posidonius) & More

[cloudsweeper]

12.40am Weds. - some fluffy cloud, but good transparency - 102S frac in shed, ready.  Moon, waning gibbous, high, SE, above Orion.  Mars sinking behind trees west of south - viewed between x50 and x200, best at x120 - detected a couple of patches of lower albedo, Neodymium filter didn't help.

Down to Orion - Trapezium in M42 good at x150, 200.  Dropping down to x17 / 4.32deg, all of Orion's Belt was seen, with room to spare.  A fine sight of the three brightest stars in a rich field.  At the very edges was field curvature and astigmatism, the latter being most noticeable with the outer bright stars Mintaka and Alnitak.  

And so to the Moon, sufficiently high to allow me to sit comfortably on a (fixed) stool.  Beautiful in the centre of the 4.32deg field, very slight green fringing around the limb, but none along the mainly jagged terminator.  Mag increased to reduce glare.  Almost all the terminator was through the highland regions, a fine spectacle.  The seas to the west appeared kind of "chalky".  Atlas and Hercules in the NE quadrant looked good, although mainly in shadow, but Posidonius further south showed much detail even though it was well lit.

I enjoyed the view through BVs briefly, going to x100 (limited by available EP pairs), then went back to Cyclops for a bit more mag.  Somewhat unstable at x200; much better x120.

Detail in Posidonius                                                                                                                                                                                                                                                                      The "ridge" to the east near the main crater rim is in fact the more pronounced rim of an inner, concentric crater, quite clear with a slim, faint shadow to the west.  Craterlet Posidonius B lies across the main rim to the north.  Others such as Daniell lie beyond.  Further detail, looking slightly paler against the grey floor was as follows:

# An arc of four small peaks NE of the near-central crater Pos A.

# A pit to the south of that, namely Pos C.

# A sinuous rille (crack) near the SW rim.

(There are some further linear rilles in the crater floor, but light conditions didn't allow spotting of those.)

Finished after 1hour 50mins.  Most enjoyable, especially as at that time I dodged the blaze of extraneous light from a neighbour's garden conservatory.

Doug.

Edited November 4, 2020 by cloudsweeper

[RobertI]

Sounds like a very successful session. I haven’t observed Orion quite yet although I have seen it peeping over the trees.

3 hours ago, cloudsweeper said:

Most enjoyable, especially as at that time I dodged the blaze of extraneous light from a neighbour's garden conservatory.

One good thing about planetary and lunar observing is not having to worry about neighbours lights!

[cloudsweeper]

18 minutes ago, RobertI said:

Sounds like a very successful session. I haven’t observed Orion quite yet although I have seen it peeping over the trees.

One good thing about planetary and lunar observing is not having to worry about neighbours lights!

That's true Rob, but a hideous orange glare - without blinds - just a few metres away does detract from the whole experience!  😠

Doug.

Edited November 4, 2020 by cloudsweeper

[Fozzie]

great report, i spent some time looking around Mare Nectaris last night, when i could drag myself away from mars..

Noticed Messier A impact rays really stood out also..

2 hours ago, cloudsweeper said:

That's true Rob, but a hideous orange glare - without blinds - just a few metres away does detract from the whole experience!  😠

Doug.

I've a street light that, is usually behind tress, but as the leaves fall it seems especially bright and detracting, so i can totally relate to that..

CS

Fozzie