Fracastorius near Mare Nectaris on the moonThe week of May 20-26 takes us from Day 13 to Day 18. This week we will highlight the moon crater Fracastorius, viewable on Saturday evening, May 25, Day 18 and located in the SE quadrant of the Field Map at M13.

Mare Nectaris on the moonFracastorius: [SE/M13; L=33°E] 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.)

There 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.


Full Moon is on Thursday.

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
Subsidence on the Moon – Moon Crater Fracastorius

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