The week of August 9-15 takes us from Lunar Day 2 to Day 8. This week we will highlight the crater Fracastorius, viewable Thursday evening.

moon crater FracastoriusFracastorius: [SE/M13] Located on the south shore of Mare Nectaris, this is one of the Moon’s best examples of subsidence. The Nectaris lavas were so heavy that the floor of Fracastorius actually cracked as it bent downward and allowed the Nectaris lavas to flow over its northern rim. If you’re lucky and have good optics and good seeing, you might actually glimpse the unnamed rille that crosses the floor from east to west just south of the center. There is a tiny 2.5-mi. crater right in the middle of this rille that may help you spot it. (Daguerre on the north shore [L13] and its adjoining unnamed neighbor have both fallen victim to the same process of subsidence.)

Fracastorius is one of the Moon's best examples of subsidenceThere are some quite small objects on the floor of Fracastorius requiring high quality optics and steady seeing. How many of these can you detect? Make a quick sketch, then come back later to compare.


The Perseid meteor shower will peak the night of August 11. The conditions are very favorable for an excellent show this year, as the Moon will not be around to interfere. The peak is likely to extend to the night of August 12 also. Under ideal conditions you could see 100 meteors per hour, but 50 is more realistic.


It is highly recommended that you get a copy of Sky and Telescope’s Field Map of the Moon, the very finest Moon map available for use at the telescope. It is available for $10.95 at and on Amazon. All features mentioned in this blog will be keyed to the grid on the Field Map and will look like this: Plato: [NW/D9]

Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission

Andrew Planck
Moon Crater Fracastorius: One of the Best Examples of Subsidence

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