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Minimum magnification for Great Red Spot

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#1 galazie

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Posted 27 July 2021 - 09:38 AM

Last night was a good night. Using my 78mm spotting scope with a 50x eyepiece, I detected the Great Red Spot on Jupiter. It was confirmed by switching to 75x.

 

so 50x and see the GRS. is it good? or usual?

 

 


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#2 DLuders

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Posted 27 July 2021 - 09:56 AM

Are you sure you saw it?  Most astronomy articles say you need at least 100x-150x to see the Great Red Spot.  


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#3 Supernova74

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Posted 27 July 2021 - 11:06 AM

Well all due respect to yourself that sounds highly unlikely to be honest.unless you have some kind of superman vision I’m unaware of.even in a 12” sct cassagrain which I own at a magnification of 70x surface detail is not great.

in my experience even at 150-200x and very good transparent seeing conditions and ideally when Jupiter is at higher altitudes still can become quite challenging at times to observe the Great Red Spot.



#4 ButterFly

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Posted 27 July 2021 - 11:11 AM

What makes you think it was the No-Longer-So-Great Red Spot?  Did you confirm your observation with some kind of software?



#5 xvariablestarx

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Posted 27 July 2021 - 11:21 AM

It is hard to differentiate the GRS from general banding, at anything less than around 150x in my experience, but my eyesight isn't the best. The first time I saw it, I had both a 8 inch Dob and a 100mm Mak on it to make sure I was seeing the same thing in both, and I was.



#6 Redbetter

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Posted 27 July 2021 - 11:32 AM

Are you sure you saw it?  Most astronomy articles say you need at least 100x-150x to see the Great Red Spot.  

The audience for answering such questions in articles is typically novices who have never seen the GRS or other planetary features being discussed.  Rather than providing a minimum, they are providing a suggested magnification where one should expect to see it.  That is a magnification where it should become obvious, rather than being a mere detection that could be made by someone already familiar with the appearance.

 

As it is, the OP is in Vietnam where Jupiter will be high in the sky, and I suspect the seeing will be quite good in a tropical climate as well.  I am not surprised that the GRS would be visible this way at relatively low power.  It is a different problem than seeing the spot in the typical roiling seeing in my backyard, desert climate.  Yet I can detect the spot at 60x with my 60ED this way.  It is not a good view in poor seeing with the present low color contrast, but the large bump sticking out of the bottom of the SEB is unmistakable when it is approaching the meridian--less so when it is on the limb.  Larger aperture makes it easier because color contrast is stronger at the same magnification, and finer features are resolved even in mediocre seeing.

 

At this time, the spot is roughly 5+ arc seconds tall and perhaps 6+ arc seconds wide depending on how you evaluate it.  That is more than large enough for detection at 50 to 60x, where the apparent size will be 250+ arc seconds by 300+ arc seconds.  


Edited by Redbetter, 27 July 2021 - 11:35 AM.

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#7 JamesMStephens

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Posted 27 July 2021 - 11:39 AM

Maybe you would like an online tool like this

https://skyandtelesc...great-red-spot/

 

Observe near the predicted transit time so you know where the spot is and you'll have more confidence deciding whether you've seen it or not.

 

Jim


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#8 payner

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Posted 27 July 2021 - 01:53 PM

What Red said is definitely the way these articles are written.  They are communicating to a general audience and are not coming at these types of recommendations/comments as one would speaking to experienced visual observers.

 

It's definitely visible in my 78 mm refractor at 50x. I would not expect an unexperienced planetary observer to see it; at higher magnification and careful observation, yes.

 

Randy


Edited by payner, 27 July 2021 - 07:03 PM.

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#9 Supernova74

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Posted 27 July 2021 - 02:07 PM

What Red said is definitely the way these articles are written.  They are communicating to a general audience and are not coming at these types of recommendations/comments as one would speaking to experienced visual observers.

 

It's definitely visible in my 78 mm refractor at 50x. I would not expected an unexperienced planetary observer to see it; at higher magnification and careful observation, yes.

 

Randy

Well i was woundering how many amateurs will be straining there eyes after this thread has finished.

trying to find the GRS on Jupiter at 50x.



#10 grif 678

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Posted 27 July 2021 - 04:57 PM

I had read lately that the Great red spot was beginning to be on the other side of Jupiter for a while?



#11 JamesMStephens

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Posted 27 July 2021 - 06:38 PM

I had read lately that the Great red spot was beginning to be on the other side of Jupiter for a while?

Ten hour rotation rate, so it's facing us several hours out of every ten.  The best visibility is when it's near meridian transit.  This online tool in #7 can help.

 

Jim



#12 payner

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Posted 27 July 2021 - 07:16 PM

Well i was woundering how many amateurs will be straining there eyes after this thread has finished.

trying to find the GRS on Jupiter at 50x.

If one has experience in planetary observation (think low contrast features) and can find steady skies and decent elevation of the planet, no straining necessary. No, do not strain at the eyepiece, relax.

 

Why not occasionally push one's self and the equipment? It can be a learning experience.


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#13 galazie

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Posted 27 July 2021 - 10:05 PM

good to hear your opinions and glad to know that I did it well. now I know that seeing the GRS at 50x and 78mm is a good performance of the scope, the weather, and the human vision.

 

yes I have no doubt that it was GRS. It was tiny, but clear, and definitely it. I confirmed the detection by increasing the mag to 75x, and cross-checking with Stellarium.

 

best,


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#14 Redbetter

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Posted 27 July 2021 - 11:13 PM

What Red said is definitely the way these articles are written.  They are communicating to a general audience and are not coming at these types of recommendations/comments as one would speaking to experienced visual observers.

 

It's definitely visible in my 78 mm refractor at 50x. I would not expect an unexperienced planetary observer to see it; at higher magnification and careful observation, yes.

 

Randy

 

For perspective, there has been conjecture whether or not Galileo would or could have seen the GRS.  He didn't record it, and his optics were quite crude compared to even the cheapest achros today.  The relevance is that he was operating at only 20x to 30x depending on the iteration of his scope.  


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#15 nibiru711

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Posted 28 July 2021 - 10:26 PM

One thing you have to remember about Jupiter is the features change over the course of the night because it rotates, too. I was using my 127mm maksutov last night and it was visible  starting at a 13mm eyepiece and above.  One thing with compared with newtonians is the red spot will be on the bottom and not the top. If it's time for it to be there(the red spot) observing with my two orion dobsonians 6 and 8 inch it will become visible starting with a 10mm most nights and it can be rather prominent feature.


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#16 Maciek_Cz

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Posted 29 July 2021 - 03:02 PM

I think you've seen the GRS for sure. I observe it very often even in a 50mm f/20 telescope with 66x magnification. In a large telescope, at low magnification and the exit pupil well above 1mm, the image of the planet is too bright to see details. 


Edited by Maciek_Cz, 29 July 2021 - 03:28 PM.

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#17 galazie

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Posted 29 July 2021 - 08:22 PM

 

 

As it is, the OP is in Vietnam where Jupiter will be high in the sky, and I suspect the seeing will be quite good in a tropical climate as well.  

Thanks for reminding me of the advantage of my location. Yes Jupiter climbs as high as near overhead here.


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#18 JamesMStephens

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Posted 29 July 2021 - 09:18 PM

Galazie,

 

What telescope do you have?  We all like pictures of telescopes on CN!

 

Jim


Edited by JamesMStephens, 29 July 2021 - 09:19 PM.

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#19 galazie

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Posted 29 July 2021 - 10:08 PM

Jim,

 

It is a Nikon spotting scope 78mm ED. I have a 50x eyepiece, and a 75x one.

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Edited by galazie, 29 July 2021 - 10:09 PM.

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#20 ButterFly

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Posted 30 July 2021 - 10:43 AM

Very nice.  If you can binoview with those, keep pushing it down to its/your limit.

 

I am having the same issue with UKS 1.  I know what it looks like through my setup, and I know where I am looking.  Is that what I should be seeing?  After some point, the answer becomes, "Who cares about the shoulds?"



#21 Redbetter

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Posted 30 July 2021 - 11:20 AM

 

I am having the same issue with UKS 1.  I know what it looks like through my setup, and I know where I am looking.  Is that what I should be seeing?  After some point, the answer becomes, "Who cares about the shoulds?"

The globular?  It is not really a visual object from what I see, too reddened and in a rich field, like Liller 1.  If we could see the red wavelengths decently in scotopic vision it would be different.  



#22 ButterFly

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Posted 30 July 2021 - 11:55 AM

The globular?  It is not really a visual object from what I see, too reddened and in a rich field, like Liller 1.  If we could see the red wavelengths decently in scotopic vision it would be different.  

That's what the PVS14 is for.


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#23 Dave Mitsky

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Posted 30 July 2021 - 01:19 PM

A list of the transit times in UT of the GRS for August is posted at https://www.projectp...eve_grs.htm#aug

 

Transit times for the entire year can be found at https://www.projectp...om/jeve_grs.htm



#24 patrickt

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Posted 31 July 2021 - 03:53 AM

     This is interesting. I myself live in the tropics, and am located about 15 degrees north of the equator. I have an old-school Vixen 80L/f15 achromat. And I have absolutely seen the GRS a handful of times in my Vixen. I always wondered why the recommended apertures and magnifications were higher. Oh, i do use the Pluto Project website for the GRS predictions.

 

     In only fair seeing, I have seen it at 133x, and more so at 171x (though somewhat mushy already, but more easily identifiable). When seeing is good, I would sometimes go down to 80x, just to test my vision, and i would (just barely) make it out. Also in good seeing, at 133x, I could also just make it out at either west or east end of Jupiter. I normally use an old Celestron  ortho for this, but for curiositys sake, have on occasion used an old Huyghenian, and see a (obviously) degraded image of it.

 

    REDBETTER - I believe you answered what I have been wondering about all this time, thank you !  Which is why I am hoping  our present monsoons will give us over here a chance to see Jupiter at opposition....

Patrick 


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#25 Dave Mitsky

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Posted 31 July 2021 - 01:13 PM

I've never tried for a low-power sighting of the GRS.  I was able to see it at 116x last night using the Naylor Observatory's 17" f/15 classical Cassegrain.  The seeing was poor and I had the scope stopped down to 12 inches with an aperture mask.  I also used a 2" light blue color filter.


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