The week of April 1-7 takes us from Day 22 to 28. This week we will highlight the moon crater Longomontanus, viewable on Tuesday morning before sunrise.

Longomontanus crater on moonLongomontanus: [SW/P7; L=22°W] Take a look at Longomontanus and before reading further, decide if something seems slightly “wrong” about the moon crater.

Location of Longomontanus on the moonLongomontanus is an exception to the rule that crater age can be determined by their relative sizes. Larger moon craters are almost always older, and when there’s an overlap, smaller craters will intrude upon the rims and floors of their larger and older cousins. The east rim of Longo has superimposed itself on top of what is obviously an older but smaller crater.


On Friday, Mars is 2° north of the Moon, on Saturday, Saturn is 1° north of the Moon, and on Sunday, Venus is 0.4° south of the Moon and an occultation of Venus will be visible from eastern North America.

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
Crater Longomontanus on the Moon
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