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Pages: 1 | 2 | (show all) bassplayer142 professor emeritus Reged: 10/03/11 Loc: Michigan Small objects on Moon sighting       #5198177 - 04/30/12 12:21 PM Edit   Reply   Quote Quick Reply   I'm becoming more interested in viewing the moon recently in greater detail, and embarking on some object identification tests. One thing that has just started to interest me is the apparent size and resolution of telescopes. Can someone point me to some good lunar objects where I can search for known craters of small size. I'm interested in calculating the smallest object I could theoretically resolve in my 16" and then seeing how small I can see. Obviously seeing conditions will play a huge role, but it will be great to add a few smallest object seen to a list and work my way down in size. Thank you in advance for any help or comments. Post Extras:       EdZ Professor EdZ Reged: 02/15/02 Loc: Cumberland, R I , USA42N71.4W Re: Small objects on Moon sighting [Re: bassplayer142]       #5198440 - 04/30/12 03:04 PM Edit   Reply   Quote Quick Reply   be sure to keep in mind that small dark circlular objects on a bright background can be seen to a fraction of a telescope's Rayleigh resolution limit. edz Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Small objects on Moon sighting [Re: EdZ]       #5198882 - 04/30/12 07:12 PM Edit   Reply   Quote Quick Reply   Estimating from this page, it seems at 0.5" seeing should allow features 1.1 miles across. But, /I believe/ that's calculated purely from the Raleigh limit. It can give you an estimate or starting point. Edz is correct, especially with dark features (linear like Cassini, or circular like Jupiter's moon shadows.) can probably be improved upon. http://www.stargazing.net/naa/scopemath.htm One thing I used to do is observe the smallest feature I could resolve, find it on a chart, then try to measure it directly or search for data on it. Give it a whirl. In a 6", the the best I could do was about 3km in diameter in good seeing. One would imagine a 16" could go well below that limit seeing permitting. Here's some more technical reading. http://www.telescope-optics.net/telescope_resolution.htm Post Extras:       GlennLeDrew Postmaster Reged: 06/18/08 Loc: Ottawa, Ontario, Canada Re: Small objects on Moon sighting [Re: Asbytec]       #5199095 - 04/30/12 09:08 PM Edit   Reply   Quote Quick Reply   I'd have thought that a tiny bright spot on a dark background would be easier to detect than a same-sized dark spot on a brighter background. But I've never devoted much cogitation to the matter... Post Extras:       dan777 professor emeritus Reged: 11/16/07 Loc: Indiana Re: Small objects on Moon sighting [Re: GlennLeDrew]       #5199160 - 04/30/12 10:19 PM Edit   Reply   Quote Quick Reply   The Armstrong (4.6 km), Collins (2.4 km) & Aldrin (3.4 km) craters are good ones to go after. Post Extras:       David Knisely Postmaster Reged: 04/19/04 Loc: southeastern Nebraska Re: Small objects on Moon sighting [Re: bassplayer142]       #5199512 - 05/01/12 02:19 AM Attachment (44 downloads) Edit   Reply   Quote Quick Reply   Quote: I'm becoming more interested in viewing the moon recently in greater detail, and embarking on some object identification tests. One thing that has just started to interest me is the apparent size and resolution of telescopes. Can someone point me to some good lunar objects where I can search for known craters of small size. I'm interested in calculating the smallest object I could theoretically resolve in my 16" and then seeing how small I can see. Obviously seeing conditions will play a huge role, but it will be great to add a few smallest object seen to a list and work my way down in size. Thank you in advance for any help or comments. Well, the Lunar Reconnaissance Orbiter Camera's Nearside Image Browser has the entire front side of the moon depicted as it would be seen from Earth with a constant illumination angle and a 145 meters per pixel resolution at full zoom: LROC Image Browser: Lunar Frontside For the smaller craters, I just "count the pixels after zooming up the image once captured into my image manipulation software. With my 14 inch f/4.6 Newtonian, I have seen small craters down to around around 1 km (0.62 miles) under excellent seeing conditions and with the proper sun angle. Below is a slightly shrunken image of the area around the Apollo 11 landing site. For approximate sizes (based on counting pixels at 145m per pixel scale), Armstrong: 4 km wide, Collins: 2.6 km, Aldrin: 2.9 km, Sabine C: 3.1 km x 2.8 km, Cat's Paw: 3.6 km x 2.6 km (difficult to see due to its shallowness). Clear skies to you. Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Small objects on Moon sighting [Re: David Knisely]       #5199571 - 05/01/12 06:36 AM Edit   Reply   Quote Quick Reply   David, nice image of one of my favorite lunar sites, thanks to Pete urging me to observe the Cat's paw. I have seen the three Astronauts and the Cat's Paw trio. Come to think of it, they were actually quite easy in very calm seeing. So, if they are about 3km in diameter, a 6" can show smaller features (contrary to what I said above.) But, the area is dotted with a plethora of more challenging craters - a worthy test of a 16". Looks like a good area to get a feel for what it can do on the moon. Post Extras:       David Knisely Postmaster Reged: 04/19/04 Loc: southeastern Nebraska Re: Small objects on Moon sighting [Re: Asbytec]       #5199591 - 05/01/12 07:03 AM Edit   Reply   Quote Quick Reply   Quote: David, nice image of one of my favorite lunar sites, thanks to Pete urging me to observe the Cat's paw. I have seen the three Astronauts and the Cat's Paw trio. Come to think of it, they were actually quite easy in very calm seeing. So, if they are about 3km in diameter, a 6" can show smaller features (contrary to what I said above.) But, the area is dotted with a plethora of more challenging craters - a worthy test of a 16". Looks like a good area to get a feel for what it can do on the moon. I kind of like the "rule of thumb" that states that the minimum approximate size (in miles) for a crater half filled with shadow to be seen visually as a true pit-like formation is about 9/D, where "D" is the telescope aperture in inches. It isn't a totally accurate rule, as the precise minimum size depends on a number of factors, but it does give one at least a useful figure to shoot for. Using that rule makes a six inch go down to at least 1.5 miles (2.4 km) in size under favorable conditions. I have seen Sabine C, the oval crater south of it, and Cat's Paw in my 9.25 inch SCT a number of times, although Cat's Paw was sometimes a little on the tough side when the sun angle was fairly high. The very first time I got to view with my 14 inch mirror after it had come back from Mike Lockwood after he refigured it, I managed to see a huge number tiny secondary impact craterlets around and west of Thebit that are not usually shown in most Earth-based images of the area. That sighting alone convinced me that the mirror refiguring job was definitely worth the money I spent on it. Clear skies to you. Post Extras:       bassplayer142 professor emeritus Reged: 10/03/11 Loc: Michigan Re: Small objects on Moon sighting [Re: David Knisely]       #5199595 - 05/01/12 07:06 AM Edit   Reply   Quote Quick Reply   Thanks for all the replies. Now I have some reading to do before these clouds part. Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Small objects on Moon sighting [Re: bassplayer142]       #5199670 - 05/01/12 08:34 AM Edit   Reply   Quote Quick Reply   Thank you, again, David. I had forgotten about the 9/D rule of thumb. You seem to be correct, as the three astronaut Craters in the image you posted are easy in good seeing. A diameter of 9/6 = 1.5 miles across would put resolution right at the Dawes limit. That might mean a 16" can see features as small as (9/16 = 0.6) miles in diameter. If we assume seeing is limited to about 0.5" arc, then using the small angle formula and limiting angular resolution to 0.5" arc, then D=(0.5" arc*384,400Km)/206,265 = 0.9 Km or 0.6 miles in diameter, as well. Edited by Asbytec (05/01/12 09:34 AM) Post Extras:       David Knisely Postmaster Reged: 04/19/04 Loc: southeastern Nebraska Re: Small objects on Moon sighting [Re: Asbytec]       #5200647 - 05/01/12 06:36 PM Attachment (40 downloads) Edit   Reply   Quote Quick Reply   Here is the section of the LRO camera's front-side mosaic showing the area around the Apollo 12/Surveyor 3 landing site. For size reference, the crater Fra Mauro B is 6.7 km across and Euclides K is 5.9 km wide. There are two smaller craters a little below (south-southeast) of the landing site which are 1.5 km (west one) and 1.6 km (east one) across that are good landmarks to where the landing site actually sits. I have seen these two fairly easily in my 14 inch Newtonian when the sun was of low to moderate elevation on the area. There is a very tiny pit nearly 600 meters across that is closer to the landing site (right below the southern edge of the "cross") than the above two craters, but I doubt it can be seen from Earth. All of these craters mentioned above were probably far beyond the view of the astronauts while on the surface. By contrast, the Apollo 11 astronauts did see the distant ramparts of Cat's Paw while they were on the surface. Clear skies to you. Post Extras:       bassplayer142 professor emeritus Reged: 10/03/11 Loc: Michigan Re: Small objects on Moon sighting [Re: David Knisely]       #5200955 - 05/01/12 10:32 PM Edit   Reply   Quote Quick Reply   Some amazing pictures and information. Im really excited to start hitting the scope on the moon and seeing what I can see. Thanks again Post Extras:       stevetaylor199 sage Reged: 09/21/11 Loc: SE Wisconsin Re: Small objects on Moon sighting [Re: bassplayer142]       #5201073 - 05/01/12 11:34 PM Edit   Reply   Quote Quick Reply   This LTVT page has yet another take on crater resolution. The short answer is that your 16" could get down to about 0.7km. Photographically, at least. Post Extras:       David Knisely Postmaster Reged: 04/19/04 Loc: southeastern Nebraska Re: Small objects on Moon sighting [Re: stevetaylor199]       #5201212 - 05/02/12 02:18 AM Edit   Reply   Quote Quick Reply   Quote: This LTVT page has yet another take on crater resolution. The short answer is that your 16" could get down to about 0.7km. Photographically, at least. Yes, but perhaps not visually. Image processing can enhance detail to make somewhat marginal craters visible in images that visually might not be easily seen. I recall the first time I saw Linne (2.4 km (1.5 miles) diameter) in my 8 inch f/7, it kind of looked more like a mound rather than much of a true deep pit, so it was clearly pretty close to the limit of the eight. It did appear as a tiny pit in my 9.25 inch, and in the 10 inch, I could see it quite clearly as a hole with a clear slightly elevated rim surrounded by a lighter ejecta blanket. With some limited tests using my old LAC chart of the Raphaeus Mountain region of the moon, I found the 9/D to be perhaps a slightly conservative but very useful figure. With the limits of Earth-based seeing most of the time, probably something in the 1 km to 1.5 km range is about the best we can do routinely with the eye (and more often, we might be limited to twice that figure). Indeed, when I was looking at the Apollo 12 landing site in my 14 inch, the only craters easily visible in the immediate area were the widely-spaced 1.5 km and 1.6 km pair about 10 km south-southeast of the landing site. Clear skies to you. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Small objects on Moon sighting [Re: David Knisely]       #5202573 - 05/02/12 07:20 PM Edit   Reply   Quote Quick Reply   Ive found the 9/D works unusually well. As mentioned there are other factors that can readjust that result but its a fair rule of thumb. Do keep in mind that in aiming for your smallest craters that the moon varies in distance significant enough to throw false positives and such if this isnt acknowledged and worked in. For general small crater 5 to 3 mikes its a shrug but under a mile or do for your huge aperture and it needs accounting for if you are to have faith in your finds. Lol, thanks for the Catspaw mention Norme - I still havent seen it nyself but not for lack of looking when I was out. I simply couldnt get out when the seeing favored it. Either Im way late snd its hopelessly lost in high sun or its sunset is past my bedtime. It is one of my most sought for things in that area though. As it is I counted myself lucky for the three astronauts under high sun with the eight. It would be fascinating if with a high sun some kind of libido dust gave away the Catspaw. As it is its met with poor seeing if its to be had and so Im left still with a pocketfull of hopes and your exceptional experiences relayed here. Good luck with tge big sixteen. Keep in mind Google Moon (within Google Earth) has a really fine measuring tool. Fun and super simple to use. What may prove maddening, particularly with old craters is measuring erided soft crater walls. Good luck and keep us informed. Pete Edited by azure1961p (05/02/12 11:43 PM) Post Extras:       stevetaylor199 sage Reged: 09/21/11 Loc: SE Wisconsin Re: Small objects on Moon sighting [Re: azure1961p]       #5207598 - 05/05/12 05:42 PM Edit   Reply   Quote Quick Reply   Thanks David. I was hoping someone would take up the issue of photo vs. visual capabilities. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Small objects on Moon sighting [Re: stevetaylor199]       #5208012 - 05/05/12 10:40 PM Edit   Reply   Quote Quick Reply   I think the BEST observers can match or slightly excede a CCD on very small scales, say 5 arc seconds or less. Larger than that and I just dint think the human eye us winning. Hyper-focused in small area the observer can put a concerted effort to maximum use. I just dont think its humanly possible to expend that same scrutiny over larger areas , and if so, not with any comparable accuracy. For all that though, I enjoy sketches MORE than ccd images. Sketches have soul. Pete Post Extras:       David Knisely Postmaster Reged: 04/19/04 Loc: southeastern Nebraska Re: Small objects on Moon sighting [Re: azure1961p]       #5208430 - 05/06/12 08:53 AM Edit   Reply   Quote Quick Reply   Quote: I think the BEST observers can match or slightly excede a CCD on very small scales, say 5 arc seconds or less. Larger than that and I just dint think the human eye us winning. Hyper-focused in small area the observer can put a concerted effort to maximum use. I just dont think its humanly possible to expend that same scrutiny over larger areas , and if so, not with any comparable accuracy. For all that though, I enjoy sketches MORE than ccd images. Sketches have soul. Pete Maybe, but from what I have seen digital imagers do, their images of the moon and planets can indeed slightly exceed the views that the eye presents. The stacking and processing simply brings up the contrast and sharpness to a point where it can be somewhat better than the actual visual view. Clear skies to you. Post Extras:       brianb11213 Postmaster Reged: 02/25/09 Loc: 55.215N 6.554W Re: Small objects on Moon sighting [Re: David Knisely]       #5209001 - 05/06/12 03:33 PM Edit   Reply   Quote Quick Reply   Quote: from what I have seen digital imagers do, their images of the moon and planets can indeed slightly exceed the views that the eye presents. The stacking and processing simply brings up the contrast and sharpness to a point where it can be somewhat better than the actual visual view. I agree. I'm a pretty experienced visual observer and see more than most people do. But I routinely make images with a 110 mm scope (4.3") in poor to bad seeing that neveretheless resolves detail that I find a struggle to see with 15 cm in good to very good seeing. Other people may well have better trained eyes than me but I've yet to meet anyone who can see the same detail that I image regularly with the same aperture. Post Extras:       Moondoggy super member Reged: 03/17/08 Loc: Jack Daniels Country Re: Small objects on Moon sighting [Re: Asbytec]       #5209135 - 05/06/12 05:14 PM Edit   Reply   Quote Quick Reply   Thankyou so much for the Scope Math site. Now thats realy helpfull ! Post Extras:       Pages: 1 | 2 | (show all)

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