The week of December 14-20 takes us from New Moon to Day 6.5. This week we will highlight the crater Arago and its surrounding domes, viewable on Sunday night.

Arago: [NE/J12] About 50 miles from the western shore of Tranquillity you will find the crater Arago (16 mi.). This is an unusual crater. In the place of a central peak you will see a substantial ridge that extends from the center of Arago’s floor to its northern rim. The evidence suggests that there was a significant collapse of rim material which simply merged with the central peak.

Arago and Arago domes on the moonArago domes: [NE/J12] On Day 4 you were able to see lunar domes around the crater Cauchy. Now you can broaden on the experience. The crater Arago has a pair of very large domes, one to its north (Arago α [Alpha]) and one to its west (Arago β [Beta]). These are two of the largest and most prominent domes on the Moon, and halfway between Arago and the crater Maclear (100 miles to its northeast) you will find a challenging group of four smaller domes. It will be a nice victory for you if you manage to spot them.

For those who are new to this blog, the author has written a book on observing the Moon: What’s Hot on the Moon Tonight? The Ultimate Guide to Lunar Observing. It is a nightly guide to the Moon’s most interesting features as they are revealed throughout the lunar month. It is highly recommended that you also obtain Sky & Telescope’s Field Map of the Moon. Lunar features that are described in the book are keyed to the grid in the Field Map.

I was fortunate in that Charles Wood, author of The Modern Moon: A Personal View, a writer for Sky & Tel, and the country’s leading authority on lunar observing was willing to write the foreword. The book is available on Amazon and from my website, (If you would like a signed copy, please order from my website.)

An e-book version of What’s Hot on the Moon Tonight is now available on iTunes and Amazon. An additional feature is that in the e-book version the longitude of lunar objects has been added to the grid reference, e.g., Plato: [NW/D9; L=9°W], meaning open the Field Map to the NW quadrant, grid D9; Plato is at longitude 9°W. The longitude of a feature is enormously helpful when you are planning a night’s observation because any object which is within 15° or so of the terminator will stand out with astonishing detail! 1

The Sun is emerging from a deep solar minimum, which is one side of the cycle in which there was a relative dearth of sunspots and solar activity for many months. Now solar activity and the appearance of sunspots is building towards a predicted solar maximum in mid-2025. Disruptions on the Sun will gradually become more frequent and more intense.

1 To find out what the longitude of the terminator will be for any night, download the free Virtual Moon Atlas onto your computer. Set the date to the night you wish to observe, then click on a crater on the terminator and read its longitude. Or use the Moon Map Pro app if you are lucky enough to have gotten it before it became unavailable on iTunes.


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
Unusual Moon Crater Arago and its Surrounding Domes

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