The week of February 19-25 takes us from Day 4 to Day 10. This week we will highlight the craters Ariadaeus (viewable on Day 6, Wed. night) and Walther (viewable Thursday).

AriadaeusAriadaeus: [NE/J11] The Ariadaeus Rille (Rima Ariadaeus) is named after this 7-mi. crater located near its eastern end. Notice that the crater has a slightly smaller companion touching it on its northeast side. Their rims are gently pushing in on each other. Can you tell which one is older?

Walther: [SW/N9] You will find this 87-mile crater adjoining Deslandres just to its east. Because it has some very complex ramparts, under an early morning Sun (which will be the case Thursday night) Walther is a strikingly beautiful object. It has an offset group of central mountains, which have been impacted by several small craters.


For those who are new to this blog, the author has written a book on observing the Moon entitled 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 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 is now available on iTunes, Amazon, and other venues. In the e-book version, the longitude of lunar features 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!

Finally, a lunar guide that clicked with me.
By Amazon Customer on March 15, 2016
Format: Spiral-bound|Verified Purchase
I stumbled upon this book by accident and I have, at long last, finally found a lunar observing guide that clicks with me. I am an experienced amateur astronomer with over twenty-five years of serious activity in many facets of the hobby.

I am not much of a lunar observer, but I do enjoy looking at it from time to time, and I’m trying to do more, mostly out of practicality. I’ve realized that confining astronomy to just moonless nights on the weekend is self-defeating; I’d only get out a few nights a year. So I’ve been endeavoring to find something enjoyable to do on any decent night, including moonlit weeknights. (And shake off this nearly 20-year deep-sky chauvinism I’ve had.)

As I’ve gotten older, I’ve noticed I’m a lot more tired on weeknights than I used to be. I’ve decided to recognize and accept this and adjust my equipment choices accordingly. After a bit of scope swapping and tweaking, I’ve assembled a weeknight lunar scope that is a 5″ Mak atop a tracking mount.

Now, back to the book. Over the years I’ve collected a decent number of lunar atlases and guides. While all are just fine, even excellent in many regards, they’ve never really worked for me at the scope. For example, to take two extremes: take any atlas, with this I can label features on the moon…and while nice, this isn’t getting me the sense of joy and exploration I’m looking for. On the other hand, take Charles Wood’s The Modern Moon, which is a wonderful book and Charles is a excellent writer, yet I’ve never been able to finish it. Yes, I enjoy science, and I very much like understanding how things formed and relate, but when you get into the details of the details, I lose interest. I’m apparently a big picture type of person.

This is my use case: I’m tired, I’ve plopped the scope out, I only have about an hour. Tell me what I should look at tonight on the moon. Tell me what’s interesting. Give me a small challenge or two. Give me a little geology, but don’t give me too much or go too deep. Give me some color — is there any history from the human side that is fascinating or illuminating? I’m tired; I don’t want to think. I just want to wonder.

It is for the above use case that Andrew’s book excels. I’ve read the first few “days” of the moon and I think it is exactly what I have been wanting. I really like how Andrew has “outsourced” the atlas portion to S&T’s Field Maps of the Moon, which also allows you to choose the normal or mirror image at will.

My only quibbles about the book are what we typically quibble about with field guides published on a small scale. I wish the paper were heavier, although being spiral bound is wonderful. I’m on the fence about the inclusion of lots of lines in which to write notes and lots of sketching circles. I think this is a nice touch, but its removal would have made the book notably thinner I believe and little more wieldy at the telescope.

I think this book will allow me to have many enjoyable “ah, that’s cool” moments as my eyes scan the moon after a long day.

After several nights of using the book at the telescope I can report that this book is indeed exactly what I was looking for. It pairs wonderfully with S&T’s Field Map of the Moon.

I also like the little challenges he gives and especially the way he gives them. He doesn’t just say that some observers have seen x number of craterlets in a crater, but let’s you know that, for example, Patrick Moore himself boasted 14. How many can you see? It’s fun to put yourself up against a master observer in that context.

I didn’t realize this when I first got the book, but I appreciate the large type. It makes it easier to read in the dim light I use at the scope.

I do not think that anyone would regret the purchase of this book.

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 when 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
What’s Hot on the Moon Tonight? The Ultimate Guide to Lunar Observing

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