The week of January 5-11 takes us from Day 17 to Day 23. This week we will highlight the moon crater Longomontanus.
Longomontanus: [SW/P7; L=22°W] Take a look at moon crater Longomontanus and before reading further, decide if something seems slightly “wrong” about the moon crater. Longomontanus is an exception to the rule that moon crater age can be determined by their relative sizes. Larger moon craters are almost always older, and when there’s an overlap, smaller moon craters will intrude upon the rims and floors of their larger and older cousins. The east rim of Longomontanus has superimposed itself on top of what is obviously an older, but smaller, moon crater.
OF ADDITIONAL INTEREST IN SPACE
On January 7, 1610, Galileo discovers the moons of Jupiter.
======================
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 www.skyandtelescope.com 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]
Credits:
Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission
- Moon Crater Cassini – Created on Imbrium floor Before Lavas Started to Flow - January 19, 2026
- Bailly – Largest Crater on Our Side of the Moon - January 12, 2026
- Longomontanus: Exception to the Rule About Moon Crater Age - January 5, 2026