Mare Crisium and Cleomedes Crater

Observation Notes:

This area was the most prominent set of features on the terminator when I checked it out tonight. The flooded basin displayed an arcuate rille sliding along the inside of the rim. The rim threw stark daggers of shadow, while the basin showed a soft transition from shadow to light, nicely demonstrating the moon’s curvature. The most prominent crater in the south end of the basin, Picard, is 23 km wide.


Mare Crisium is a basin, created during the Nectarian epoch, while the mare material is of the Upper Imbrian epoch. Mare Crisium is an elongated crater that is 100 km wider in the E-W direction, although it doesn’t appear that way because it is close to the edge of the moon from our vantage point. Cleomedes Crater is a flat basined crater with a central peak that is 126 km in diameter and 2.7 km deep.

Subject Mare Crisium and Cleomedes Crater
Classification Lunar Maria and Crater
Position Northeast
Age/Phase 17 days old
Size* Mare Crisium: (dia. 500 km E-W x 400 km N-S);
Cleomedes Crater (dia. 126 km x depth 2.7 km)
Date/Time 10/30/04 – 11:45 PM
Observing Loc. Flagstaff, AZ – Home
Instrument Orion SVP 6LT Reflector (150 mm dia./1200 mm F/L)
Eyepieces/Mag. 10 mm + 2X Barlow (240X)
Seeing 3/10

* Based on published data.