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  #1  
Old 06-11-2018, 06:17 AM
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mental4astro (Alexander)
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Any gravitational lensing effects that can be seen through scope?

Hi all,

I'm trying to recall if there are any gravitational lensing effects that can be seen through an amateur size scope. This following from the Smiley Face found by the HST.

I think there is, but the memory just doesn't gel...

Anyone able to shed some light so I can refocus my thoughts?

Alex.
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  #2  
Old 06-11-2018, 06:28 AM
glend (Glen)
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Certainly there are, at least ones that can be imaged using amateur equipment. Look here:

https://www.astrobin.com/182048/

Captured with a homemade Newt.

There is a thread about this area on CN:

https://www.cloudynights.com/topic/5...dss-j10384849/

He used a TEC140.

I doubt observationally it could be seen.
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  #3  
Old 06-11-2018, 07:49 AM
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Atmos (Colin)
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Although most gravitational lens' are considerably fainter than their faint galaxy counterparts there are a couple of brighter ones. I wouldn't imagine that any of them would be visible visually without at least 30" of aperture though.
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  #4  
Old 06-11-2018, 07:57 AM
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mental4astro (Alexander)
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Thanks Glen. It is visual observation I am asking about though.

Since posting my original question, I seem to recall Einstein's Cross or Einstein's Ring being visible - though the "Einstein Ring" is more of a collective term for an complete or long annular effect.

Alex.
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Old 06-11-2018, 08:04 AM
Wavytone (Nick)
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Alex Einstein’s Cross is possible visually in a 25”-40” dob...

https://www.cloudynights.com/topic/4...mateur-scopes/

If someone has a 30” at a star party there are few to try.
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  #6  
Old 06-11-2018, 09:37 AM
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mental4astro (Alexander)
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Thanks Wavy!
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  #7  
Old 06-11-2018, 09:38 AM
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Shiraz (Ray)
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Can only comment on gravitational arcs. The brightest that I am aware of is described in the paper linked here http://www.iceinspace.com.au/forum/s...d.php?t=161884.

The arcs in Abell 370 and 2667 may also be worth a look, but these things really are are very dim and will be challenging - if they are possible at all at around mag 18+ (integrated). Would have to be a great experience if you could see one though.

Cheers Ray

Last edited by Shiraz; 08-11-2018 at 03:38 PM.
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  #8  
Old 08-11-2018, 10:05 AM
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mental4astro (Alexander)
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Thanks Ray!

Your link has allowed me to find 3 candidates, including the Andromeda Parachute!, probably the easiest, though a real horizon grazer for us. Blooming heck, an object that is more than 9 billion light years from us! Three times further than the Virgo Quasar. Through amateur size scopes! WOW!

Alex.
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  #9  
Old 08-11-2018, 02:25 PM
pmrid (Peter)
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Guys, this is a real teaser! I just have to try a capture. But finding RA and Dec for these objects is proving to be surprisingly difficult. Can anyone provide refs for some of the more likely candidates please?

Peter
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Old 08-11-2018, 02:50 PM
Wavytone (Nick)
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Clearly there’s a need for a book “Gravitational Lenses for Southern Observers”.

here’s one in Pegasus at mag 17
https://en.m.wikipedia.org/wiki/Einstein_Cross

Last edited by Wavytone; 08-11-2018 at 03:02 PM.
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  #11  
Old 08-11-2018, 03:42 PM
pmrid (Peter)
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Thanks Nick. That'll give me something to point at. I make that sitting more or less on top of PGC 69457 - an eliptical of .9x.3 arc/mins and +15.44 apparent mag. As far as I can tell, and assuming we're working on J2000 precession, that should be about 1 second in RA and 1.3 in Dec away so it ought to be in the FOV if I can push the resolution well enough. What fun!!

Peter
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Old 08-11-2018, 09:39 PM
Wavytone (Nick)
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Peter I’ve got the resolution, but not the aperture well not visual anyway.

Slowly I’m collecting the pieces to put a camera on the MK91 and auto guided, this would be one heck of a target for a night.

It’s a pity the scopes at Stromlo were destroyed ... that would have been just possible - visually - using the 30” Reynolds.

Last edited by Wavytone; 08-11-2018 at 09:50 PM.
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Old 09-11-2018, 07:40 AM
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Well, a brief reality check has persuaded me that this particular object will remain closed to me - with the theoretical resolution (Dawes Limit of 4.56 seconds/aperture in inches) of my longest FL scope is only about .5 seconds and since this object is only 1 second away from an elliptical galaxy - well, you can see the problem. I have a 10" newt with a lovely Suchting conical mirror in it but even that might not be enough to see this but factoring in the usual limits imposed by even the best local seeing would conspire against me. I'll give it a try but I won't be holding my breath.

Peter
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Old 09-11-2018, 09:59 AM
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Peter, the Dawes' Limit ONLY works between two point sources of light, like a star, which are diffraction patterns, an Airy Disk, and in particular the Dawes' Limit is between two Airy Disks and how diffraction patterns interact.

For an extended object, this all changes, and the resolving power of say a knife edge line is less than 1/10th that of the Dawes' Limit.

This is why the Cassini Division was discovered with a 2.5" scope in 1695!, which is impossible if the Dawes' Limit applied to extended objects. And the Encke Division is visible in a 7" scope - I've seen it in a 7" Mak. The Encke Division is 0.05" - WAY smaller than the Dawes' Limit for a 7" scope!!!

If you still have any doubts, have a look at really high quality images of Saturn using 7" or 8" scopes, and the Encke Division is clearly visible in these. If the Dawes' Limit applied to extended objects, the Encke Division would not be visible.

And if you still have any doubts, if you have seen the Cassini Division in an 80mm scope, YOUR SCOPE JUST EXCEEDED ITS DAWES' RESOLUTION LIMIT!!! and you've whitnessed this yourself! The Cassini Division is not a challenge for the modest Skywatcher ED80. Yet somehow no one questions this!

This is a common misnomer about the "resolution limit" of scopes. The information regarding it is both only half explained, and then poorly understood by most people.

The actual application of how the Dawes' Limit and Raleigh Limit are acquired are like I said, for a pair of diffraction patterns. When it comes to extended objects, this diffraction patter is totally disrupted, and the TRUE resolution limit of a scope is significantly smaller than the Dawes' Limit.

I've only come to find out this in the last few weeks myself! I had a suspicion something wasn't quite "kosher" when I started seeing very fine details on the Moon, and on doing some trig calculations I was staggered to see that these structures were much finer than the quoted resolution limit for 7" and 8" scopes. But it is no mistake as I've come to find out

I explain it a bit more in this post: http://www.iceinspace.com.au/forum/s...5&postcount=10 and in the rest of that thread it is talked about some more.

Peter, I suggest you reconsider your thinking about not following through with this project

Alex.

Last edited by mental4astro; 09-11-2018 at 10:23 AM.
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  #15  
Old 09-11-2018, 03:25 PM
pmrid (Peter)
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G'day Alex. Yes. You're right of course. I got stuck on the Dawes Limit in the context of Einsteins Cross which usually appears as 4 star-like images and I figured this would be the place where an Airy Disk would be sure to overlap. Happy to be proven wrong of course.

Peter
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Old 09-11-2018, 07:40 PM
Wavytone (Nick)
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Peter,

It’s one hell of a challenge. A 4”-5” reaching galaxies at mag 19 - and in colour - tells me it’s not impossible and a factor of 2 in aperture should make a useful difference.

From the double stars I’ve tried the MK91 easily has the resolution to split it cleanly in 8/10 seeing near the meridian - if it was magnitude 11 or brighter.

But at mag 17 the time needed to image this is s serious problem. I suspect it’s feasible, if “success” is an indistinct blob distinguishable from a star, and it could be full spectrum monochrome - doesn’t have to be colour. In this respect a mono camera with no Bayer filter would be the go.

You’d have to be phenomenally lucky seeing wise, and guiding at sub second of arc rms the whole time.
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Old 09-11-2018, 08:03 PM
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Quote:
Originally Posted by mental4astro View Post
Thanks Ray!
Your link has allowed me to find 3 candidates, including the Andromeda Parachute!, probably the easiest, though a real horizon grazer for us...
Alex.
Ah man, the Andromeda patch of sky is at Zenith around 9:15pm where I am right now. Wish I brought something bigger than the 102 Mak with us...
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  #18  
Old 10-11-2018, 09:41 AM
pmrid (Peter)
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Quote:
Originally Posted by Wavytone View Post

You’d have to be phenomenally lucky seeing wise, and guiding at sub second of arc rms the whole time.
Yes. The best I can do is my fast (F3.8) 10" mirror and hope for good seeing. I know its a long shot but what the heck? While that scope is grinding away, I can go to the other extreme and image with my FSQ85.

Summer nights up here are often not that great for seeing though. Even when weather cooperates, the upper atmosphere frequently boils like a kettle.

Peter
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