The week of November 15-21 takes us from Day 12 to Day 17. This week we will highlight Mare Frigoris.

Mare Frigoris: Only Lunar Mare Patch Not CircularMare Frigoris: [NW-NE/D6-13; L=54°W] This is the only mare patch that isn’t even roughly circular, although its northern boundary has an intriguing curve to it which may support the “Gargantuan hypothesis” (below). As the lunation progresses, you will notice how Mare Frigoris appears to connect Oceanus Procellarum to the eastern maria. It has been suggested that Frigoris is the northern rim of an enormous pre-nectarian feature called Gargantuan Basin, which spanned 1,500 miles from the western shores of Procellarum to the middle of Mare Serenitatis. This is nearly 70% of the Moon’s diameter and would have been an impressive wallop! See if you can trace the entire outline of this putative basin tonight. Do you think the Gargantuan proposal has merit?


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
Mare Frigoris: Only Lunar Mare Patch Not Circular
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