The week of January 30 to February 5 takes us from Lunar Day 10 to Day 15. This week we will highlight Mare Frigoris, located in the NE quadrant of the Field Map and viewable on Tuesday evening.

Gargantuan BasinMare 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-Gargantuan Basin on the moonnectarian 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?


Moon at apogee on Saturday, Full Moon on Sunday.


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 on the Moon and the Gargantuan Hypothesis

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