The week of June 12-18 takes us from Day 25 to Day 1.
This week we will highlight the rille Rima Marius on the moon (in the NW quadrant of the Moon Map at H5) and viewable early Tuesday morning.
Rima Marius: [NW/H4-5] Just to the northwest of the moon crater Marius C is Rima Marius, a sinuous rille that extends for 150 miles. When the rille starts out, it is about 1.2 miles wide (~1 arc-second), but it tapers down to only 0.3 miles. Because a line can be easily distinguished when a point of the same diameter is totally invisible, you should be able to see the rille when its width is well below the theoretical limits of your telescope. See how far you can extend Rima Marius across the lunar surface.
OF ADDITIONAL INTEREST IN SPACE
On Wednesday, Jupiter is 1.5° south of the Moon, and on Friday, Mercury is 4° south of the Moon.
======================
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