Plato Craterlets

[Alkaid]

Good seeing last night.  Using the 4" TAL 100RS Achromatic Refractor.....I knew the limitations of a 4" aperture but had read reports that Craterlet 'A' could be seen with this aperture and a low angle of illumination.   The illumination was just right, long shadows creeping across Plato at 8pm last night. 

Craterlet 'A' was seen....quite difficult to resolve but after looking for a long time it was definitely there.

I am pleased for the TAL, it has good optics.

[michael.h.f.wilkinson]

Well done! I spotted Plato through bins yesterday, but clouds rushed in before a scope could be brought out. I have spotted some of the craterlets with my C8, but am surprised your 4" picked it out. Well done

[Alkaid]

Well done! I spotted Plato through bins yesterday, but clouds rushed in before a scope could be brought out. I have spotted some of the craterlets with my C8, but am surprised your 4" picked it out. Well done

Yes, it was very hard to be honest Michael.  I saw it, then the seeing would cause a slight problem and then after a few seconds I detected it again...it kept going like this in a cycle, over and over, seeing dependent.

So this morning I decided to google the craterlets to see if a 4" should be able to do it....general consensus is that it can do 'A' on a good night under the right conditions,  but definetely not 'B' 'C' or 'D'.  So with a bit of luck I am pleased that I managed 'A'!

[laudropb]

That is a very good capture. I have struggled to see A with my Dob unless the seeing conditions were very good.

[Alkaid]

I wonder if imaging would capture it better....hundreds of stacked frames might even show the smaller ones?  I want to get into this and try...

By the way, as a very rough calculation...

Craterlet 'A' is 2.44km across.  Using the distance to the Moon as 400,000 km, the angular diameter of 'A' is 1.26 arc seconds.  That's very close to what TAL say about their refractor, 1.3 arc seconds I believe (sorry I haven't got the detail in front of me right now).   It does explain to me why it was so hard and why the illumation needed to be just right, seeing good etc.   I must have been very lucky indeed.

[michael.h.f.wilkinson]

I have seen A, B, and C with the 8" and have some images backing that up, but I need bigger iron to see the rest  I suppose

[John]

The Plato craterlets are a good test of seeing and optics. The TAL certainly has a good objective.

I've seen "the big 4" with my 4" and 4.7" refractors on good nights under favourable illumination. C & D are sometimes seen as one.  My "best ever" was 10 with my 12" dob under superb conditions which enabled 400x plus to be used.

Theres a good guide to these features here:

http://www.cloudynights.com/topic/34841-guide-to-plato-craterlets/

[michael.h.f.wilkinson]

Very useful reference. I think I must have seen D at some point, but didn't log it.

[Alkaid]

I've seen "the big 4" with my 4" and 4.7" refractors on good nights under favourable illumination. C & D are sometimes seen as one.  My "best ever" was 10 with my 12" dob under superb conditions which enabled 400x plus to be used.

Brilliant! 

[goodricke1]

Haven't attempted these, but did identify crater Carlini S last night. 2.5 miles diameter in the Mare Imbrium, viewed with 13mm plossl and x2 Barlow on the 8SE. One never knows when conditions will allow further observations of these elusive rascals -

[cathalferris]

It's not the diffraction limit of the optics that limits the visibility of small craters under low angle illumination, it's the contrast between the crater and the surrounding maria. If there was an area of only a few hundred metres across that was hugely brighter  than the surroundings, it'll get picked fairly easily even though it's well below the resolution of the scope that you could detect it with.

You can see another example of that with the Hubble images from 2004 of Ceres, seeing the bright spots, and the angular diameter of the bright spots is well under the resolution of Hubble.

It doesn't alter the fact that being able to detect the craterlets is a good test of a telescope. It's a test of the mean transfer function, not the resolving capability. The shadowed craterlet floor is a contrast against the surrounding basalt, and the larger the shadow the easier the detection.