Mons Gruithuisen Gamma summit craterlet

[Nyctimene]

Observed the waxing gibbous moon yesterday evening with the 12" f/5 Hofheim traveldob. Slightly hazy/cloudy (cirrus) skies, average seeing (concentricity of Hesiodus A flashing up at mag 167x). The terminator was very close to the two lunar domes  Montes Gruithuisen Delta and Gruithuisen Gamma. Once again, I tried to spot the summit craterlet at the peak of Gruithuisen Gamma, about 900 m diameter (Rükl; other sources say 2.2 km), with magnifications of 167x and 250x, without success as usual. A small, but bright albedo spot at the NE slope was misleading me first (it's not visible in the LunarMap HD app); but after consulting the Luna Cognita handbook, I found this spot mapped well (fig. 16.27). So, one of the lunar nemesis features (for me) remains unresolved still after many years of trying. Has anybody on here spotted the summit craterlet? (should be possible with 12").

Thanks for reading

Stephan

Edited September 26, 2023 by Nyctimene

[Nik271]

My telescopes are up to 180mm in aperture, and so I did not think it's even possible for me. But your mention of the potentially 2.2km wide craterlet made me look it up. It is actually 2.5 km so a whopping 1.25'', theoretically within reach of even a good 4 inch. I will try to look in good seeing and when terminator is nearby, the craterlet is quite shallow which is probably the main difficulty.

 

Edited September 26, 2023 by Nik271

[Nyctimene]

Thank you, Nik271, for the excellent information. Where did you look it up?, seems to be a very useful website!

I'll try again, and will wait for a very low angle of illumination.

Patience is a virtue - just spotted for the first time Rima Sharp (!) with the 12". Rather good seeing, allowing mag 250x (6mmf UWA). The Rima was visible for five to ten seconds in moments of very quiet air several times, clear, but at the limit of vision. I'd compare it to the search for Rima Messier with the 18". Pleased and content!

Stephan

[Mr Spock]

It's LROC quick map https://quickmap.lroc.asu.edu/?extent=-90%2C-26.9451471%2C90%2C26.9451471&id=lroc&showTerrain=true&queryOpts=N4XyA&layers=NrBsFYBoAZIRnpEBmZcAsjYIHYFcAbAyAbwF8BdC0yioA&proj=10

Use the search function, then the draw tool.

[davidc135]

On 26/09/2023 at 21:34, Nyctimene said:

Thank you, Nik271, for the excellent information. Where did you look it up?, seems to be a very useful website!

I'll try again, and will wait for a very low angle of illumination.

Patience is a virtue - just spotted for the first time Rima Sharp (!) with the 12". Rather good seeing, allowing mag 250x (6mmf UWA). The Rima was visible for five to ten seconds in moments of very quiet air several times, clear, but at the limit of vision. I'd compare it to the search for Rima Messier with the 18". Pleased and content!

Stephan

Like you I've failed on a few occasions to spot the m. g. createrlet in a planetary 8.5'' Dob, but have just managed the northern part of Rima Sharp in the v. good seeing that we sometimes get.   David

[Mr Spock]

If you can pick out the four main craterlets in Plato then you should be able to see this. They are A (2.7km), B (2.4km), C (2.4km) and D (2.1km). I can see all four with my 100mm.

I find my 12" can get sub 1km in excellent seeing. In Plato I can split craterlet P into 2 craters; I've yet to pick up the third which is 0.5km - it should be possible I think.

[John]

Often with these small lunar features the illumination needs to be "just right" to catch them clearly. Sometimes these windows of effective illumination only last a couple of hours.

The rille (some sections especially) that runs down the Vallis Alpes and the smaller Plato craterlets are other examples of such features.

 

[Nik271]

On 26/09/2023 at 21:34, Nyctimene said:

 

Patience is a virtue - just spotted for the first time Rima Sharp (!) with the 12". Rather good seeing, allowing mag 250x (6mmf UWA). The Rima was visible for five to ten seconds in moments of very quiet air several times, clear, but at the limit of vision. I'd compare it to the search for Rima Messier with the 18". Pleased and content!

Stephan

Nice! I've tried for Rima Sharp numerous times with my biggest scope, the skymax 180, but I've found it quite a challenge, there was one occasion where I think I saw the northern part in brief moments but can't say it was a definitive view. It's a waiting game for the right moment.

Another of my favourite challenges are the trio Armstrong, Aldrin and Collins craterlets in Tranquility. Armstrong is easy, the other two I've seen only a couple of times. I think it's not just the width of the craters but also how steep the incline of the sides,  the more shallow is harder.

[jonbosley]

Here is a recent observation report I made in average seeing.

Mons Gruithuisen Domes Lunation Day 11 Observation 4” f11 Refractor 204x
Mons Gamma the dome on the west side is casting a shadow to the southwest. The north eastern part of the dome is in sunlight with the summit also brightly illuminated. No summit crater was  visible.
Mons Delta  is casting a more prominent shadow to its southwest towards mons Gamma with the summit a slightly darker albedo than mons Gamma. The isolated raised highland  is well seen to the south of Mons Delta, this is casting in westerly shadow over the newly named Sinus Viscositatis. The crater Gruithuisen P located just east of mons Delta is well seen with much of its floor in shadow.
The third dome NW is much smaller but could be clearly observed just to the west side of Mons gamma. Mons NW has a bright illuminated summit and like its larger neighbor casting a small shadow towards the southwest.

[melsmore]

5 hours ago, jonbosley said:

Here is a recent observation report I made in average seeing.

Mons Gruithuisen Domes Lunation Day 11 Observation 4” f11 Refractor 204x
Mons Gamma the dome on the west side is casting a shadow to the southwest. The north eastern part of the dome is in sunlight with the summit also brightly illuminated. No summit crater was  visible.
Mons Delta  is casting a more prominent shadow to its southwest towards mons Gamma with the summit a slightly darker albedo than mons Gamma. The isolated raised highland  is well seen to the south of Mons Delta, this is casting in westerly shadow over the newly named Sinus Viscositatis. The crater Gruithuisen P located just east of mons Delta is well seen with much of its floor in shadow.
The third dome NW is much smaller but could be clearly observed just to the west side of Mons gamma. Mons NW has a bright illuminated summit and like its larger neighbor casting a small shadow towards the southwe

Do you know exactly when this observation was made?

[jonbosley]

On 04/12/2023 at 05:22, melsmore said:

Do you know exactly when this observation was made?

4” Refractor UTC 8/28/2023. Time covered a number of hours with other observations  covering approximately 03.00-0500 UTC. 87% illumination, Alt covering 29°-31°, Location Central Texas (unfortunately I cannot give exact location on a public forum).  

Here is an image that I took with my 18” on a Lunation day 10, so very similar outlay except the shadows where shorter and not as much detail obviously. I have not been able to have a clear observation of the summit crater on Gamma using my 4” as of yet, probably as I use other telescopes when the seeing is very good. 
Image details. UTC 05/12/2022 10 day Moon. Very good seeing 1.6 arcsec but gusting winds. 18” reflector, f16.5, 3x barlow, Player One Mini 429 camera, red 610nm filter. Central Texas. 

Jon

Edited December 6, 2023 by jonbosley
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[melsmore]

Thanks @jonbosley, nice picture. They're on my lunar list and looks like I have a wider observation window than I thought.

Edited December 6, 2023 by melsmore

[jonbosley]

Here is some update reporting on the Domes from LROC https://www.lroc.asu.edu/posts/1133

 

Jon