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Cosmic Challenge: Lunar craters Armstrong, Aldrin, and Collins

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Cosmic Challenge:

Lunar craters Armstrong, Aldrin, and Collins

July 2019


Phil Harrington


This month's suggested aperture range

6-inch (15 cm) to 9.25-inch (23.5 cm) telescopes




Best lunar phases
(days after New Moon)

Craters Armstrong, Aldrin, and Collins

Lunar crater trio

5-6, 19-20


Last month, I challenged you to find all six of the Apollo landing sites.  This month, to commemorate the 50th anniversary of Neil Armstrong's and Edwin Aldrin's historic landing and moon walk, we return to Mare Tranquilitatis, the scene of Apollo 11, to find three small craters that bear the names of that historic mission's crew members.

Above: Craters Arago, Manners, Ritter, Sabine and Dionysius with Lamont structure and Apollo 11 landing site. Source: NASA / LRO_LROC_TEAM

Above: Finder chart for this month's Cosmic Challenge.
Click on the chart to open a printable PDF version in a new window.

The reason you are reading this article right now is because I am a product of the 1960's space race, when the United States and the former Soviet Union battled each other for supremacy in space.  The goal, set by President John F. Kennedy in 1961, was "to land a man on the Moon and return him safely to the Earth" by the end of that decade.  It seemed impossible, given that we had just barely scraped outer space at the time with Alan Shepard's suborbital flight.  But eight years later, Kennedy's dream was realized, if posthumously, when Neil Armstrong took that "one small step for (a) man, one giant leap for mankind."  It was one of those moments in history that, if you were alive at the time, you can recall exactly where you were.  Me?  I was transfixed to the television screen (we even had color TV, although the Apollo 11 camera was only black-and-white) in the living room of my childhood home in Rowayton, Connecticut.  I was hooked for life.

The names of the three Apollo 11 astronauts are now permanently commemorated on the surface of the Moon by a trio of small craters that lie near the mission's landing site along the southwestern shore of Mare Tranquilitatis.  Since the largest, named for mission commander and first man on the Moon, Neil Armstrong, only measures 3 miles (4.8 km) across, however, high magnification and steady seeing will be needed for any hope of seeing them.

The three Apollo astronaut craters see first light five nights after New Moon.  The best opportunity for finding them, however, comes a night later, when the Sun has risen high enough to also light a pair of twin craters to their west.  Those two craters, Ritter [19 miles (30.6 km) diameter] and Sabine [18 miles (29 km) diameter] ride the Tranquility coastline, tucked just inside the mare's southwestern corner.  Since New Moon is on July 2, prime viewing will be on the evenings of July 7 and 8. If you're a morning person, then set your alarm for July 21 -- ironically, exactly half a century after the landing!  I can't think of a better way of commemorating the event, can you?  (But if it's cloudy, then July 22 will also do.)

Once Ritter and Sabine are in view, switch to about 200x and scan to the east of the latter.  Look for the lone crater Maskelyne, some 9 crater diameters to the east of Sabine.  Armstrong crater lies almost exactly between the two.  Scanning further back toward Sabine, a second, slightly smaller crater can be found.  That's Collins, 2 miles (3.2 km) in diameter.  Finally, the least distinct of the three, Aldrin, is also 2 miles (3.2 km) across and found about halfway between Collins and Sabine.  All three Apollo craters are nearly equally spaced, with Armstrong and Collins slightly closer to each other than Collins to Aldrin.

As you look their way, play back that famous line in your mind and realize the history this area has seen.  "Houston, Tranquility Base here.  The Eagle has landed."  Tranquility Base lies some 14 miles (22.5 km) to the southwest of Collins.

Back in March 2018, CN'er
Tom Glenn shared some great photos that he captured of the region in the forum using his Celestron C9.25 Edge HD and ASI224mc camera.  In addition to taking some magnificent images, Tom really did his homework, offering links to various NASA images, as well.  I'd encourage you to visit the thread if you are unaware of it.  I especially like his cropped close-up, showing the three craters of interest, as well as an unusual triple crater dubbed the Cat's Paw.  On my chart above, the Cat's Paw is that little dimple just to the upper left (northwest) of the Tranquility Base marker.  Tom points out that the Cat's Paw is the only lunar feature that the astronauts saw while on the surface that we can also see through our backyard scopes -- but it's tough!  Can you spot it, too?

Above: A pair of images of the Apollo 11 landing region taken by Tom Glenn.  The top image shows the three craters named for the astronauts, while the bottom image is a cropped close-up of Cat's Paw and its relative location to Tranquility Base.  Source: Tom Glenn.  Used with permission.

Above: This close-up view of the Cat's Paw and West crater was taken from lunar orbit by Japan's SELENE spacecraft (better known in Japan by its nickname Kaguya). Apollo 11 landed just west (left) of West crater in an area that appears relatively bright.  Source: NASA

Above: Cat's Paw Hills (crater rim) as viewed from the lunar surface.  Source: NASA

Before I close, permit me a small plug for the book upon which this Cloudynights feature is based.  A revised, second printing of Cosmic Challenge: The Ultimate Observing List for Amateurs has been released by my publisher, Cambridge University Press.  Inside are updated data tables and charts for finding various solar system objects, such as Pluto and Vesta, as well as improved renditions of my many eyepiece sketches that accompany each of the 187 challenges encompassing more than 500 individual objects.  The book is available from Amazon.com (isn't everything??) as well as "better bookstores everywhere."

Until next month, remember that half of the fun is the thrill of the chase.  Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy, including Cosmic Challenge: The Ultimate Observing List for Amateurs.  Visit www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2019 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


  • Dave Mitsky, JimP, John O'Hara and 2 others like this


Jul 11 2019 06:38 AM

Fun challenge! Thank you Phil! This can be done in fair seeing with a 6" telescope. Using a 6" f/15 Cassegrain I could hold Armstrong steady at 180X before sundown with the moon at 8 days, 13 hours old. Once the sun had set and the sky darkened, Collins could be seen as the seeing allowed, but Aldrin was only hinted at. This was in turbulent air downwind of a mountain range. For those with a steady sky, I'm sure even Aldrin would be achievable this late in the lunar month with a 6".

    • JimP and PhilH like this

Have seen, drawn and imaged the Apollo 11 landing site including Armstrong, Aldrin and Collins many times, first with an AP 6” F/12 Super Planetary apo April 12, 1989.  These three craters are not the real challenge. The real challenge is seeing the triangle of craters including “Cat’s Paw” that direct you to the landing site itself. Born in 1950 I too am a Space Age guy and I followed every Mercury, Gemini and Apollo mission with Great interest and enthusiasm.


Jim Phillips

    • PhilH and Tyson M like this

Thanks for your kind words!  Don't forget to set your alarm for tomorrow or Monday morning.  That's when all three craters will be at their best.  By Tuesday, the Sun will have set from their locations.

    • Dave Mitsky and Special Ed like this
Dave Mitsky
Jul 22 2019 02:26 AM

Before I went to bed on Sunday morning I took a look at the waning gibbous Moon with the 6" f/8 Orion SkyQuest XT6 Dob that I keep in my garage for casual observing. It had been somewhat clear much earlier in the night and I had observed Jupiter and Saturn but then the sky grew overcast. However, the Moon was now in the midst of a sucker hole but clouds were heading that way. I had wanted to see if I could see the craters named after the Apollo 11 astronauts but 150x that my 8-24mm Hyperion Mark III zoom eyepiece produced at full zoom wasn't enough.

I went inside to get my 4.5mm Tele Vue Delos (267x) but by then thin clouds were beginning to cover the Moon. On top of that, the 0.6mm exit pupil produced by the Delos did a wonderful job of displaying the floaters present in both of my eyes. It was pointless to go even higher in power so I put the telescope back in the garage.


I only managed to get one afocal iPhone photo of the Moon and it turned out to be slightly out of focus.


Dave Mitsky

Attached Thumbnails

  • Attached Image: Moon July 21 IMG_9169 Processed CN.jpg
    • PhilH likes this

Tough break on the weather, Dave, but I can recognize the big craters around the Apollo 11 landing site in your pic.


Conditions were near perfect here Sunday morning allowing me to make this sketch of Tranquility Base 50 years and a few hours after the historic landing.


Thanks for the challenge, Phil.  smile.gif   I had seen Armstrong and Aldrin in the past but had not detected Collins until a couple of days ago.  A good way to commemorate this anniversary.  

    • Dave Mitsky and PhilH like this
Dave Mitsky
Jul 22 2019 12:13 PM

Tough break on the weather, Dave, but I can recognize the big craters around the Apollo 11 landing site in your pic.



I'm pretty sure that I see Moltke and can definitely make out Sabine and Ritter.  It's unfortunate that I wasn't able to take a better photograph.





It was either raining or completely overcast last night.

Dave Mitsky


    • PhilH likes this

Yes, that brightish dot just inside the Mare is Moltke.  A little ways to its left are Sabine and Ritter and if you follow that line, the next bright dot is Dionysius.  smile.gif 

Dave Mitsky
Jul 22 2019 06:14 PM

Moltke stands out a bit better in this shot that I took on July 19th.

Attached Thumbnails

  • Attached Image: Moon July 19 IMG_9150 Processed CN.jpg
    • PhilH likes this
Jul 28 2019 02:32 PM
A very interesting article.I have been doing alot of lunar imaging lately,and have managed to get some really good shots of the Sea of Tranquility. Although I doubt that my little 90mm doublet will allow me to see these small craters.
    • PhilH likes this

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