13 replies to this topic

[fcathell]

After catching Titan, Rhea, Dione and Tethys in my C90 Mak at 208X tonight, I figured I would try for the craterlets in Plato.  In 45+ years of serious observing, I've never looked for these, so I thought I would try after reading a post here on CN about them. Not a trace, even after waiting until the moon got reasonably high. One thing I became acutely aware of was all the stuff I can see in my eye and any traces of dirt on the eyepiece (I assume) field lens. After a little experimenting with eyepieces I found that 165X was about all I could do on the moon without being seriously aggravated by floaters, other unworldly looking things, etc in my eye.  I assume that this is due to the small exit pupil caused by the combo of the 90mm aperture and magnification.  It appears that a 0.5 mm exit pupil is about all I can tolerate on the moon.  This is not an issue on Saturn or Jupiter, but neither is the glare/brightness factor.  I may have picked the wrong moon phase also to look for these craterlets.  I think I read that the optimum time is around a 12 day old moon. Then again, maybe a 90mm aperture is just not adequate for visual detection. Comments from you seasoned lunar observers are definitely welcome.

 

Frank

[John O'Hara]

You could do one of two things: Get a binoviewer or use more aperture.  Even an inexpensive binoviewer can work well on the moon and planets (I have an old Burgess unit).  The .5 mm exit pupil is also my "magic" number, where my floaters take over with a single eyepiece.  

 

I've only made one serious attempt to see craterlets in Plato, a successful one.  I used my astronomy club's 14" Meade LX 200 with an Orion 16.8 mm MegaVista eyepiece (212x).  The seeing that night was exceptional.  I've not tried in smaller scopes, but you've given me a challenge.  

 

Incidentally, this is Challenge 128 in Phil Harrington's book, Cosmic Challenge, which would be a great guide for this task.

[Don Taylor]

I have seen a few (the one near center, the one about the same size about 1/2 way to the S rim, and the two slightly smaller ones nearly touching also about 1/2 way NW from center to rim) with my deforked 90mm ETX but generally have the same problems with floaters as you.  I do a bit better with the 4" ED or the ETX125TB.  0.5mm is my limit too but I do better with a little larger exit pupil. I see some really strange tree limb like objects floating by.........

Edited by Don Taylor, 08 November 2019 - 10:36 PM.

[RadioAstronomer]

Interesting. I just came back from observing the moon (also in Tucson) with my TV 102 at 176x (5mm Pentax SMC Ortho eyepiece) and saw three Plato craterlets. Two of them were very easy.

[PirateMike]

Keep trying Frank, you will see them sooner or later. 

 

 

Miguel   8-)

 

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[Codbear]

Frank,

 

I believe it's all about seeing and aperture to identify as many craterlets as possible. I've seen 6 craterlets with my C14 Edge HD. I just got a new NP101is and will be interested to see how many it can pick off with its 4" aperture.

 

Also John...thanks for the reference. I have just purchased Phil Harrington's book you alluded to and I'm sure I will enjoy the challenges. Interesting that there are 187 challenges - you might say it's a real "killer" of an endeavor!

[Astro-Master]

HI Frank, I read a post on CN about a year or so ago about the Plato craterlets, it had some nice photos with the diameters of the craters.  I tried for them first with my Stellarvue 105mm APO, I think I saw three or more.  The next night I tried with the 180mm  Intes Mak-Cass, I think I saw 5 or maybe 6, I should have taken notes.

 

I don't usually look at the moon, I'm more of a deep sky observer.  I'll have to give it a go again and this time I'll take some notes

[Asbytec]

Plato Challenge. One of the great observing threads on CN.

https://www.cloudyni...lato challenge

[NorthernlatAK]

I just came back in from observing and was focused on the aristarchus plateau region, but took a gander at Plato to see if I could see anything. To my surprise, I was able to see several bright albedo spots where the craters are at 266× in my 8" dob. Would this count as an observation of the craterlets?

[Astro-Master]

Plato Challenge. One of the great observing threads on CN.

https://www.cloudyni...lato challenge

 

Thanks Asbytec, that was the great post I remembered reading that made me want to take the Plato Challenge.

[Redbetter]

Some of this is likely familiarity with what these craterlets look like in different conditions and apertures, and detection vs. seeing it more as a crater.  Finding them first in somewhat larger aperture provides some discrimination between the real and imagined.  It has been awhile since I studied them, but have found the big 4 or 5 accessible with small apertures when conditions are favorable.  Tonight I took a quick look with the 60ED then the 80ED.

 

The 60ED showed A as a vague brighter spot not quite centered.  I had some indication of it even at medium power but confirmed at 90 and 120x.  The floaters/texture of my eye are a challenge for this at 0.5mm exit pupil, but I had vague indications of two others:  B and the C/D pair (not individual).  I wasn't really sure on either, the seeing was not that steady and I didn't recall what the orientation should be.  (I did a check on Rigel just to make sure I was seeing Rigel B.)

 

I brought out the 80ED to see if it revealed more.  The scope was cooling some, but its own thermals were not the primary obstacle:  even after a time I noticed that some local thermal effects were impacting the seeing for considerable spells.  Despite that A was seen immediately in a better stretch.   I cycled through 100, 120, and 150x trying to confirm the others and felt I was seeing them more frequently and in the same orientation, but not quite consistently enough. I was getting a wide triangular lighter albedo affect on the crater floor next to one of the suspects, which I believe was B.  

 

I haven't kept score with the 80 on these, but on good nights I think I have been able to recognize C and D individually with it (though marginally), and perhaps detected E as well.  I know I have done so with the 110ED and 127 Mak.

[AJK 547]

Plato Challenge. One of the great observing threads on CN.

https://www.cloudyni...lato challenge

Many thanks to you CN’ers (and that excellent thread!) in nudging me into this challenge!  It took a great night of transparency and ‘seeing’ for me to bag ‘em as true craterlets (not albedo) in the C8-A (Delos 8 + Baader 2.25X Barlow).  ‘F’ and ‘W’ came in and out of view over the next hour.  Too bad those nights of excellent seeing are sooooo rare.

 

A later session I tried my C6 (w/Delos 3.5) on the craterlets (during a night of <average seeing), only 'A' resolved as a ‘pit’... B, C/D just ‘albedo’ sadly.  Too much power + below avg seeing = no success!

 

My next challenge is the Vallis Alpes ‘Rille’ on a night of excellent seeing and transparency.  Any recommendations on what it takes to discern the rille as a true depression?

Edited by AJK 547, 09 November 2019 - 08:21 PM.

[BillHarris]

Another good thread on Plato's craterlets is

https://www.cloudyni...ato-craterlets/

The OP tried to see these craterlets at a colongitude of about 51*. Plato has a longitude of about 9*, so this makes for a solar elevation of about 40*. The three largest craterlets are about 1 arc-sec (about 1.5mi/2.4km) in size, which is marginal in a 100mm scope, and likely impossible at that sun elevation. I'd try again about 1 to 1-1/2 days after Plato sunrise, at a colongitude of 20* to 25*. I've been able to barely discern the largest craterlets under a low sun and good seeing with my Questar 3.5.

Good luck and keep trying!

[Asbytec]

My next challenge is the Vallis Alpes ‘Rille’ on a night of excellent seeing and transparency. Any recommendations on what it takes to discern the rille as a true depression?

As with the craterlets, seeing is king. Hang in there. IME, the rille is tough in a 6 inch even when seeing is nice, but it can be done even if marginally so. Keep at it until things come together one night.