This weekend we return the Moon, with several targets for both Friday and Saturday evenings. Most targets are new, others we visited last month, but they will now show new details under different lighting. Under good seeing conditions, that is, with steady skies, these features will offer a wealth of good detail and nice contrast. Each target includes the minimum size instrument that can be used to see the object. Send me your comments and observations!
July 12th, 10:30 PM PDT
Posidonius - Longitude: 29.9° East, Latitude: 31.8° North
This walled plain will be right along the terminator, partially in sun and shadow. It is nicely paired with the adjacent crater Chacornac, which is fully illuminated. Posidonius is circular, 58 miles in diameter, with fairly high walls. The crater Posidonius B punctuates the wall, while other craterlets litter the floor. Be certain to note Rimea Posidonius, a 48 mile by 1 mile series of rilles along the floor of this walled plain. Min. instrument - 50 mm refractor.
Rima G Bond - Longitude: 35.0° East, Latitude: 33.0° North
Just to the east of Posidonius, this rille stretches north to south for 91 miles, mimicking the terminator in its orientation. It punctuates the mountains of Lacus Somniurum, slashing through their length, and ends at the crater Hall J to the north. Min. instrument - 200 mm reflector.
Hercules - Longitude: 39.1° East, Latitude: 46.7° North
A 71 mile diameter circular formation that is paired nicely with its neighbor, Atlas. You should have excellent views of its steep slopes, terraces, and on the floor the crater Hercules G, three hills, and dark stained sunken areas. Min. instrument - 50 mm refractor.
Fracastorius - Longitude: 33.0° East, Latitude: 21.2° South
A 75 mile diameter formation with damaged walls and a northern edge overrun by lava from Mare Nectaris. It has fairly steep slopes containing many craterlets, and ruins of an emerging central mountain. Min. instrument - 10x binoculars.
July 13th, 10:30 PM PDT
Theophilus - Longitude: 26.4° East, Latitude: 11.4° South
61 mile diameter formation forming a great trio with Cyrillus and Catharina. It has very high walls and a flat floor containing a 1400 m high central mountain with four peaks. Min. instrument - 10x binoculars
Mare Tranquillitatis - Longitude: 28.0° East, Latitude: 8.0° North
This sea is one of the largest Mare on the Moon at a nearly circular 424 miles in diameter. Note its numerous wrinkle-ridges, and especially along its western periphery, a nice series of rilles. Min. instrument - 10x binoculars.
Aristoteles - Longitude: 17.4° East, Latitude: 50.2° North
We've visited this crater before, but not under these conditions. The terminator is quickly gobbling it up, and different features will be visible. The walls are 11,200 feet high, and contain terraces. Craterlets and rilles litter an extensive floor. A nice pair with nearby crater Eudoxus. Min. instrument - 50 mm refractor.
Rima Burg - Longitude: 26.0° East, Latitude: 45.0° North
This rille is 61 miles long and 2 miles wide. It is perpendicular to and west of the crater Burg, in the Lacus Mortis, an old crater filled with lava. This should be a spectacular area under tonight's lighting conditions. For the Rima, min. instrument - 200 mm reflector.
Mark Wagner is a life-long astronomy enthusiast and deep sky observer. He has spent the past twenty years popularizing amateur astronomy in the San Francisco bay area through his writing and community building. A past president of the San Jose Astronomical Association, he founded what is now the annual Golden State Star Party in California. Please post if you have comments, questions, sketches or images you've taken of the targets mentioned above.