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Moon: Plato crater 12" RCX saw 2 craterlets good?

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#1 Pess

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Posted 17 February 2008 - 02:07 PM

Last night I had the best (out of 2) observing conditions in 8 weeks. Skies were 8 with luna directly overhead.

For centuries men have looked at the moon and used the crater Plato to check their telescopes resolution. The basin of Plato is so smooth it looks like someone poured in Jello Pudding and let it harden!.

The only thing marring this smooth surface is a small number of craterlets of varying size.

As a challenge to see just how well I could get my Meade 12" RCX to function I set it out early and let it acclimatize.

I also laid out a succession of eyepieces and Powermates designed from low power wide-field all the way up to about 600x which is my scopes theeoretical 'best' magnification.

Field reducer was removed. Attempts were made with and without a polarizer and/or a Lumicon Deep Sky filter for LP reduction.

At best, and intermittently, I was able to discern two craterlets in plato's basin.

I am in a heavily light polluted area.

Anyone with experience looking at the moon with a 12" think this is about what is to be expected performance? The filters were worthless in any and all combinations. In fact after finishing moon observations i easily seperated Polaris from its double but with the $200 Lumicon in place I could no longer see Ursa Minor! I was disappointed to say the least but inexperience in this filters use may be partially to blame.

Commentary?

Pesse (Stock image of Plato) mist

#2 Schiaparelli

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Posted 17 February 2008 - 03:04 PM

Hello Douglas,

I observe yesterday Plato too and I could detect three craterlets with my TMB 115/805.
I think your 12" RSC can show you much more.
You don't shoud be disapointet. A lot things could happen, that you can't see more.
Perhaps the RCX wasn't complete cool down, or the seeing conditions are not good enough for seeing more details, or the RSC wasn't perfect kollimate.

So, I think you should give your fine and great telescope a new chance to look through.

clear skies, Jürgen

#3 frank5817

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Posted 17 February 2008 - 07:51 PM

Pess,

Nice report and attached image of Plato. :cool:

Frank

#4 David Knisely

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Posted 18 February 2008 - 01:56 AM

Last night I had the best (out of 2) observing conditions in 8 weeks. Skies were 8 with luna directly overhead.

For centuries men have looked at the moon and used the crater Plato to check their telescopes resolution. The basin of Plato is so smooth it looks like someone poured in Jello Pudding and let it harden!.

The only thing marring this smooth surface is a small number of craterlets of varying size.

As a challenge to see just how well I could get my Meade 12" RCX to function I set it out early and let it acclimatize.

I also laid out a succession of eyepieces and Powermates designed from low power wide-field all the way up to about 600x which is my scopes theeoretical 'best' magnification.

Field reducer was removed. Attempts were made with and without a polarizer and/or a Lumicon Deep Sky filter for LP reduction.

At best, and intermittently, I was able to discern two craterlets in plato's basin.

I am in a heavily light polluted area.

Anyone with experience looking at the moon with a 12" think this is about what is to be expected performance? The filters were worthless in any and all combinations. In fact after finishing moon observations i easily seperated Polaris from its double but with the $200 Lumicon in place I could no longer see Ursa Minor! I was disappointed to say the least but inexperience in this filters use may be partially to blame.

Commentary?

Pesse (Stock image of Plato) mist


I have seen up to around 10 small craterlets on the floor of Plato in my 10 inch under good seeing conditions when the sun-angle is low. However, more commonly, I am lucky to see the "Big Four" craterlets which are between two and three kilometers in diameter. When the sun angle is quite high, a number of these craterlets can be seen as tiny white dots when seeing is good. In fact, I regularly can see the largest craterlet near the center of Plato as a tiny white dot in my 80mm f/5 refractor. It is not resolved as a true craterlet of course, but at least it is "detectable". Here is some information about the craterlets in general:

** MAJOR CRATERLETS ON THE FLOOR OF PLATO (see attached image below)**
(Rim-to-rim diameters 1 km or larger, based on Lunar Orbiter IV images. (Plato Rim diameter from point on the cusp of the inward bowing feature north) of faulted rock (West Rim Bow-in) to east rim edge = 62 miles (99.8 km). NOTE: Letters used below are *not* standard IAU secondary crater designators.

APPROXIMATE CRATER DIAMETERS
(+/- 0.2 miles uncertainty)
The "BIG FOUR" (+1)
A = 1.7 miles (2.7 km) B = 1.5 miles (2.4 km) C = 1.5 miles (2.4 km) D = 1.3 miles (2.1 km) W (on west-northwest wall) = 2.0 miles (3.2 km)
NOTES: Although many amateurs rarely seem to see very much on the apparently smooth dark floor of Plato, the above craterlets are the ones most often reported by those lucky enough to get really good seeing. "A" is the easiest of this group due to its fairly prominent ramparts, and has been reported in a 4 to 5 inch aperture, although the unresolved "bump" of craterlet-A's ramparts is visible in only a 3.1 inch. 3 or 4 of these craterlets can sometimes be observed under low sun angle and in good to excellent seeing in apertures 6 inches and *larger*. These four can sometimes be "detected" as very tiny white spots in 3 to 5 inch scopes during the full moon, although to show them all as true pits often requires a 7 or 8 inch aperture. The "East Wall Pit" is a much larger irregular feature (4 miles across) which often hides in the shadow of the eastern wall during the lunar mornings. It may or may not be an impact crater. There is also a small nearly rimless craterlet "W" low on the west-northwest wall north of the west-rim bow-in which is about 2 miles across. It is considerably more difficult to observe than its size would indicate, as the sun has to be at just the right angle to allow any shadow to fill even part of it to make it visible.

The "Little Four"
e = 1.2 miles (1.9 km) f = 1.0 miles (1.6 km)
g = 0.94 miles (1.5 km) h = 1.4 x 0.8 miles (2.2 x 1.3 km)
NOTES: Craterlet-e has been sighted in a good 8 inch, but craterlet-f may take a bit larger scope to see with any regularity. "e" tends to hide in the long early morning shadows, as "f" does also in the low lunar evening. The Lunar Orbiter shots of Plato show that "h" is a tiny double craterlet with 0.9 and 0.8 mile diameter components, forming an elongated 1.4 x 0.8 mile feature visible in larger apertures, but not fully resolved. Again, very high lunar sun may allow some of these cratelets to be "detected" as tiny white spots near full moon. The "Big Four", and the "Little Four" probably represent most of the craterlets on the floor of Plato which might be visible to amateurs using moderate to large apertures under excellent seeing.

The "Tiny Nine"
i = 0.7 miles (1.2 km) j = 0.6 miles (1.0 km) k = 0.7 miles (1.3 km) l = 0.6 miles (1.0 km) m = 0.7 miles (1.2 km) n = 0.7 miles (1.1 km) o = 0.7 miles (1.1 km) (double craterlet) p = 0.7 miles (triple craterlet) q = 0.6 miles (1.0 km) (double overlapping crater)

NOTES: These are *extremely* difficult to observe even in large apertures as anything other than tiny white spots or rimless pits, although i, j, m, and o2 have been imaged by Maurizio Di Scuillo using a CCD camera on a ten inch Newtonian optimized for high resolution planetary work. Craterlet k has a very small pit to its west and will be tough to resolve easily. Craterlet m is a fairly shallow bowl with little in the way of a rim, so it is more difficult than its size would indicate. "n" is a very small rimless pit just to the east of a tiny white spot which is often mistaken for a crater (may be a small mound or ejecta blanket). Craterlet o is a double craterlet, which forms a 1.3 mile x 0.7 mile elongated feature. p is a triple, consisting of 0.7 mile, 0.6 mile, and 0.3 mile craterlets in close promimity, which might be detectable in very large apertures as a single almost rimless 1.5 mile x 0.7 mile feature (not resolved). Craterlet q is two very small overlapping craterlets which form a single 1.3 mile x 0.6 mile feature. Lunar Orbiter images show a large number of smaller pits down to 0.25 miles across on the floor of Plato, but the above three "families" are probably the only ones which have much of a chance of being seen visually from Earth.

Attached Thumbnails

  • 2199672-PlatoCraterletGuideSmall.jpg


#5 Pess

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Posted 18 February 2008 - 11:31 AM

Thanks David. Maybe I saw more than i thought as I was looking for something that actually looked like a crater instead of a 'white dot'. I'll try again when the heavens open up.

I think my biggest problem is getting light pollution. Also the electric focuser on the RCX is difficult to use. The relative reading jumps all over so you can't step it in fine focus mode for perfection. You kinda have to eyeball it as you go and hope you don't overshoot.

Pesse (I may have to go with external focuser) mist

#6 Stephen65

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Posted 25 February 2008 - 08:01 AM

Seeing is everything when it comes to the craterlets and you also have to look at the right time of the lunar month. I can usually see 2-4 in my 5" refractor and most times I will see 4 in my 10".

#7 desertstars

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Posted 25 February 2008 - 10:47 AM

Good seeing and a hefty dash of patience. The best I've done so far is six on a night of pretty good seeing. The smallest of those I saw did not show clearly all of the time. Staying glued to the eyepiece I was able to catch a few magical moments of stillness that revealed two more craterlets than I might otherwise have seen.

Most nights, with merely average seeing, I consider four to be a good number.

#8 Pess

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Posted 25 February 2008 - 01:46 PM

thanks guys. If I good a good night of seeing I'm going to try an see what I can get with the SBIG and a few hundred frames.

Pesse (If at first you don't succeed, cut and paste from a moon atlas.) Mist


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