Sunken Yet Uplifted

The lunar crater Posidonius
By Frank McCabe

Posidonius on the Eastern Shore of the Sea of Serenity
  
  On this cold morning in early December the most eye-catching crater resting on the
concave sloping rim of Mare Serenitatis was 96 kilometer diameter Posidonius. The
Posidonius cratering event likely occurred 150 thousand years or more after
Serenitatis formed a ring basin. The subsequent floor uplift and fracturing within
Posidonius created a large angular block and ridge margin that you can see arching
parallel along and just inside the outer eastern crater rim. At 17.5 days into the
lunation, the floor of Posidonius appeared much brighter than the dark margin lava
of Serenity. Eleven kilometer crater A near the center of Posidinius was clearly
visible in the poor seeing as were craters B, J, and M arching out from the rim to
the north. Beyond these craters encircled  by the Lake of Dreams is 25 by 30 km.
oval “island crater” Daniell, formed by a shallow angle impact before the greater
Posidonius event took place. South from Posidonius and again along the shore of
Serenity is the 63 km. flooded crater LeMonnier. Nearly all of the west rim of this
tilted crater and its floor are covered by the dark margin lava of the Sea of
Serenity.
  
  Sketching:
  
  2H graphite pencil on 5 x 8 inch index card
  Date: 12-8-2006 11:30 to 12:15 UT
  Temperature: -14 °C (6° F)
  clear, cold winds
  Pickering scale: 3/10
  10 inch f / 5.7 Dobsonian  161X
  Colongitude:127.5°
  Lunation: 17.6 days
  Illumination: 86.3 %         
  
  Frank McCabe