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Can the disc of the seventh planet be seen in a 70mm scope?

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#1 Tropobob

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Posted 03 December 2021 - 06:02 PM

I am just curious if a quality 70mm refractor will show the small disc of Uranus. 

 

I previously owned a 60mm F15 Unitron, with ortho EPs and it showed all stars with a aerial disc similar in size to the planet, thus making the identification impossible.  

 

Last night, I used my 80mm Vixen (F7.7) Apo with a Fuju orthoscopic EP, and its color and disc was unmistakable at 50x.  When I used some basic plossl EPs, I needed 83x to be certain. 

 

So, I am seeking personal experiences about what was smallest-sized, quality refractor that was used to see and identify the planet?

 

 

 

 

 


Edited by Tropobob, 03 December 2021 - 06:39 PM.

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#2 Redbetter

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Posted 03 December 2021 - 06:17 PM

I usually use a bit more magnification with scopes this small (closer to 100x as a starting point), but yes, Uranus' disk is apparent down to 60mm aperture and certainly with the 72EDII.  Neptune is much more difficult at these apertures, and requires more magnification.  It doesn't resolve well with the 60 and is marginal with the 72 going from memory.  An 80 does a little better, but still a tough match.

 

BTW, forgot to mention this at start, Uranus is #7, Saturn is #6


Edited by Redbetter, 03 December 2021 - 06:25 PM.

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#3 Bean614

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Posted 03 December 2021 - 06:41 PM

Uranus is the 7th Planet.  



#4 Tropobob

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Posted 03 December 2021 - 06:43 PM

I usually use a bit more magnification with scopes this small (closer to 100x as a starting point), but yes, Uranus' disk is apparent down to 60mm aperture and certainly with the 72EDII.  Neptune is much more difficult at these apertures, and requires more magnification.  It doesn't resolve well with the 60 and is marginal with the 72 going from memory.  An 80 does a little better, but still a tough match.

 

BTW, forgot to mention this at start, Uranus is #7, Saturn is #6

Thanks for that.  I must not be pushing magnifications to the necessary values.   

 

6th planet- I must be getting old-timers disease!   smile.gif

 

(Heading is now corrected) 



#5 CHASLX200

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Posted 03 December 2021 - 07:15 PM

A very good 70mm can do 300x as i have easy with my SW 70mm scope.


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#6 Mark9473

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Posted 03 December 2021 - 07:19 PM

I previously owned a 60mm F15 Unitron, with ortho EPs and it showed all stars with a aerial disc similar in size to the planet, thus making the identification impossible.


No difference in the twinkling?

#7 Tropobob

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Posted 03 December 2021 - 10:28 PM

No difference in the twinkling?

I thought not.   



#8 csrlice12

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Posted 03 December 2021 - 10:33 PM

It's still #7 till a doomsday machine shows up...or the IAU declares it a nonplanet.



#9 Wow!

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Posted 04 December 2021 - 12:42 AM

It's still #7 till a doomsday machine shows up...or the IAU declares it a nonplanet.

Jupiter is a failed proto-star anyway, so let's reclassify it first :)


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#10 Astrojensen

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Posted 04 December 2021 - 04:15 AM

I wouldn't get too hung up on which size telescope is needed to show this or that. Much depends on one's visual acuity, something which is partially outside our control. It's not so important, what others need to see any given feature, what's important is what YOU, yourself, need to see it. It's obviously fun to compare what you might need to see a given feature, compared to others, but you shouldn't feel inferior or less worthy as an observer, just because you need more than average aperture to see any given object or detail. This is not a competitive sport, it's a hobby.  

 

 

Clear skies!

Thomas, Denmark


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#11 skysurfer

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Posted 04 December 2021 - 04:31 AM

Disk of Uranus ? You mean its rings (which are a sort of disk with a hole in it in which the planet itself is) ?
No, only Saturn's rings are visible in a small scope.



#12 Astrojensen

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Posted 04 December 2021 - 04:43 AM

Disk of Uranus ? You mean its rings (which are a sort of disk with a hole in it in which the planet itself is) ?
No, only Saturn's rings are visible in a small scope.

??? Is there a nuance to the difference between the words "disc" and "disk" I am not aware of?

 

Referring to the visual appearance of a planet in the eyepiece as having a disc, when it has an appreciable diameter, is normal, or so I thought. 

 

 

Clear skies!

Thomas, Denmark


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#13 ETtheExtraterrestrial

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Posted 04 December 2021 - 11:41 AM

So I have never seen Uranus’s rings and just by doing a quick search online I’m not sure it’s possible. Considering they weren’t observed for the first time until 1977 and that was from a plane with scientific instruments that’s a big leap in amateur instruments. One of the only earth bound images that pops quickly is 10M observatory using near infrared.

My guess would be people see an aberration of some kind and associate it with the rings. They’re extremely faint.

There has been times they’re visible as a glint with large amateur scopes but the angle and location have to be perfect.

Again, not discounting folks and if I’m wrong I’m wrong.

#14 Mark9473

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Posted 04 December 2021 - 11:46 AM

Nobody's seeing the rings, it was just skysurfer's misinterpretation of the word disc.
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#15 Redbetter

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Posted 04 December 2021 - 04:49 PM

I wouldn't get too hung up on which size telescope is needed to show this or that. Much depends on one's visual acuity, something which is partially outside our control. It's not so important, what others need to see any given feature, what's important is what YOU, yourself, need to see it. It's obviously fun to compare what you might need to see a given feature, compared to others, but you shouldn't feel inferior or less worthy as an observer, just because you need more than average aperture to see any given object or detail. This is not a competitive sport, it's a hobby.  

I disagree with this assertion for the target and aperture ranges under discussion.  While visual acuity varies, at its core this isn't so much about acuity as it is about the size of the scope.  These small apertures are down in the range where it doesn't matter if your acuity is perfect, the diffraction effects and dimming of the image (since Uranus and Neptune are becoming lower and lower surface brightness) make it more difficult to distinguish the planetary disk.  You can apply all the magnification you want to make up for acuity (scale) differences, but that won't do anything to address the diffraction aspect and it will make the image dimmer, further impacting color perception.

 

Neptune is particularly tricky with a 60 to see clearly as a disk.  It becomes more of a judgement call where one is best served comparing to stars of similar magnitude to look for differences.  2.3" with a 60mm scales to 0.27" with a 20".   Not coincidentally, the latter is about the limit I have with the 20" for trying to resolve asteroids when the seeing is steady enough for it.  

 

Anyway, as one makes small incremental increases in aperture, it is apparent how much more noticeable the resolution of planetary discs become.

 

This is very similar to the aperture to diffraction pattern size for resolving double stars.



#16 Astrojensen

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Posted 04 December 2021 - 05:09 PM

I disagree with this assertion for the target and aperture ranges under discussion.  While visual acuity varies, at its core this isn't so much about acuity as it is about the size of the scope.  These small apertures are down in the range where it doesn't matter if your acuity is perfect, the diffraction effects and dimming of the image (since Uranus and Neptune are becoming lower and lower surface brightness) make it more difficult to distinguish the planetary disk.  You can apply all the magnification you want to make up for acuity (scale) differences, but that won't do anything to address the diffraction aspect and it will make the image dimmer, further impacting color perception.

 

Neptune is particularly tricky with a 60 to see clearly as a disk.  It becomes more of a judgement call where one is best served comparing to stars of similar magnitude to look for differences.  2.3" with a 60mm scales to 0.27" with a 20".   Not coincidentally, the latter is about the limit I have with the 20" for trying to resolve asteroids when the seeing is steady enough for it.  

 

Anyway, as one makes small incremental increases in aperture, it is apparent how much more noticeable the resolution of planetary discs become.

 

This is very similar to the aperture to diffraction pattern size for resolving double stars.

My intention wasn't to say that the laws of physics aren't important. What I tried to say was: "Relax, it's a hobby, don't get too frustrated, if you can't see something with aperture X, that someone else can". 

 

 

Clear skies!

Thomas, Denmark


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#17 Tropobob

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Posted 04 December 2021 - 05:40 PM

Thanks for your kind words Thomas, but I was just curious, not frustrated. My smallest scopes are two apo 80mms.  (Orion triplet, F6 and my favorite; a Vixen 80mm F7.7)   I personally think they are a wonderful balance of usefulness and portability.  I have never owned a 70mm of similar quality and I was just wondering how capable they were in comparison to a 80mm.  Its just a knowledge thing, I would like to know when talking with people what scopes may suit them and their capabilities.


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#18 CHASLX200

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Posted 04 December 2021 - 05:49 PM

Not much of a diff from 70mm to 80mm. The 80mm digs down a little deeper for deep sky and planets are a tiny bit brighter at the same power.



#19 Tropobob

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Posted 04 December 2021 - 07:10 PM

Not much of a diff from 70mm to 80mm. The 80mm digs down a little deeper for deep sky and planets are a tiny bit brighter at the same power.

Thanks Chasl, I get it.  I thought that it may have the difference between seeing and recognizing the tiny disc of Uranus. However, now to my surprise, some have seen the disc with only a 60mm.   



#20 CHASLX200

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Posted 04 December 2021 - 07:28 PM

Thanks Chasl, I get it.  I thought that it may have the difference between seeing and recognizing the tiny disc of Uranus. However, now to my surprise, some have seen the disc with only a 60mm.   

I have never viewed that planet much. But the disk is easy to tell from a star with a good 70mm at 200x and up. Used over 1000x on Sat and Jup many times with my 14.5" and bigger Dobs but never tried Unranus. If i can't see detail i just don't bother to look at a object.



#21 gnowellsct

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Posted 04 December 2021 - 07:48 PM

I am just curious if a quality 70mm refractor will show the small disc of Uranus. 

 

I previously owned a 60mm F15 Unitron, with ortho EPs and it showed all stars with a aerial disc similar in size to the planet, thus making the identification impossible.  

 

Last night, I used my 80mm Vixen (F7.7) Apo with a Fuju orthoscopic EP, and its color and disc was unmistakable at 50x.  When I used some basic plossl EPs, I needed 83x to be certain. 

 

So, I am seeking personal experiences about what was smallest-sized, quality refractor that was used to see and identify the planet?

This is the refractor group.  Some will come forward who have seen the disc in their finders, and patiently drawn belt details.


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#22 vtornado

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Posted 04 December 2021 - 10:49 PM

I have seen it with my 80mm scope in the summer.  I'm fairly certain 70 can disc it.

No features, just a pretty, tiny, blue disk.

 

Neptune on the other hand I found a challenge.  My 80 ran out of light before I could get enough magnification to be certain it was a disk.


Edited by vtornado, 04 December 2021 - 10:54 PM.

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