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"A scope under 7 inches aperture is of no use observing planets"

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#1 RichA

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Posted 23 October 2020 - 02:51 AM

-John Texereau, paraphrased.  I read a book he wrote about his observing experiences.  I believe expanded, he meant that clear, verifiable visible features were better presented (especially so-called "transient" features) and more reliably recorded using scopes above 7 inch aperture.  He was also adamant that observations done in anything but pristine seeing were suspect.

 

 


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#2 db2005

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Posted 23 October 2020 - 03:06 AM

Maybe true for strictly scientific purposes - but with the advent of the HST and giant telescopes one could easily argue that any telescopes smaller than, say 2 meters are "of no use". It doesn't mean that observing planets with smaller scopes is less enjoyable, though. A mere 2-4 inches of aperture can show you things that that can open a person's mind to the universe and a mindset of curiosity and scientific thought that would otherwise not be opened. It could be argued that these qualities of small scopes are at least of "some use".


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#3 BGazing

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Posted 23 October 2020 - 03:47 AM

Last night I observed Mars in my 4 inch refractor, binos, 180x.

I saw southern polar cap, northern polar hood, Mare Acidalium with Lunae Lacus link, Deucatonis Regio like a huge bright promontorium into a dark sea, and the three pronged tentacles of Solis Lacus area. Seeing was not good enough for additional features and there appeared to be no limb haze and orographic clouds like there were a few nights ago. Better seeing also brings out finer coloring features of the surface, breaks it down into differently shaded areas.

Mars is 60 million kilometres away. So I'd say a 4 inch refractor was useful and helped me observe planetary features on a small rock really really far away. On a night of good seeing I saw incredible things in my friend's 140mm APO, clearly better than anything my C8 has shown me. If anything, in our climate it is the seeing that puts the cap (and not the aperture) almost always, and it is the quality of the optics which allows me to see the most under those conditions.


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#4 Asbytec

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Posted 23 October 2020 - 03:52 AM

...he meant that clear, verifiable visible features were better presented (especially so-called "transient" features) and more reliably recorded using scopes above 7 inch aperture.  He was also adamant that observations done in anything but pristine seeing were suspect.

If he meant that, it's interesting. I observed planets for nearly a decade in a 6" aperture in some of the consistent best seeing I am aware of. Seeing of 8/10 or better was common, and better than that was not a once in a lifetime experience. He may be right about some detail being suspect in less than pristine seeing. When seeing is nearly perfect, it's nearly perfect or better on shorter time intervals allowing some very fine detail to emerge. 

 

One example is seeing a small craterlet on Plato's floor less than a mile in diameter with a 6" aperture. To show some scale, that's about 0.72" arc. However, it was not always visible. I saw it exactly three times over a few minutes when already very good seeing became even better. Another example is observing Jupiter. In good seeing, Jupiter certainly looks nice. At times it is "etched". Sometimes, smaller portions of the planet might reveal some very tiny detail to emerge then fade. Sort of a micro seeing effect because I do not recall the entire planet showing that level of small, fleeting detail at once.

 

Detail in the martian polar caps is visible, too, including the current apparition. Surface albedo on Ganymede and an "apparent" very slight elongation of Io when compared to Europa's more circular (borderline extended object) disc. I am not sure I have seen that level of detail when seeing was modest or worse. Such things seem to occur more readily when seeing is already very nice, with even nicer moments at brief random intervals. I noted them reliably enough (unmistakable, actually) in a 6" aperture. But, sure, maybe more reliably in a 7" aperture. 


Edited by Asbytec, 23 October 2020 - 03:58 AM.

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#5 lee14

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Posted 23 October 2020 - 05:35 AM

Right. And Percival Lowell used the 24 inch Clarke to map out the extensive canal system on Mars. It's a rather absurd assumption to denigrate smaller apertures over their lack of resolving power, when the more significant variable is the skill and perception of the observer.

 

Lee


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#6 planet earth

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Posted 23 October 2020 - 05:37 AM

I don't believe everything I read.


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#7 David Gray

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Posted 23 October 2020 - 06:18 AM

George Alcock is more famous for his comet and nova discoveries; but part of what got him more to those was the criticism of his views of planets with a 4” refractor that were dismissed by several BAA notables.

 

The full Linked Article is only available to members but it goes on to tell how those observations were ultimately vindicated. 

 

https://www.britastr...urnal_item/5752

 

The sheer amount of detail on those Jupiter sketches was because it was during an SEB Revival.

 

In the hands of an accomplished observer there is a lot to see on planets with less than 7”.  In fact those willing to hone their skills have shown that many times over the years......and still are.......

 

What such an observer can do with 3”.......  http://alpo-j.sakura...0/m201017k1.jpg


Edited by David Gray, 23 October 2020 - 06:20 AM.

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#8 Jon Isaacs

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Posted 23 October 2020 - 06:44 AM

-John Texereau, paraphrased.  I read a book he wrote about his observing experiences.  I believe expanded, he meant that clear, verifiable visible features were better presented (especially so-called "transient" features) and more reliably recorded using scopes above 7 inch aperture.  He was also adamant that observations done in anything but pristine seeing were suspect.

 

Rich:

 

What did Jean Texereau really say?  Did he really say it was of no use to observe the planets in a scope less than 7 inches?  That is very different than saying that clear, verifiable features were better seen in scopes larger than 7 inches. We all know that's true.  We also know that difficult, transient features are best seen in excellent seeing.  It's worth remembering that Texereau was not an amateur, he was a professional who was responsible for many larger scientific telescopes.  

 

https://fr.wikipedia...i/Jean_Texereau

 

Roland Christen in his Cloudy Nights article "What is the Best Planetary Telescope" also recommends scopes larger than 7 inches for viewing the planets.  

 

"Whatever system you choose, you might want to consider your local viewing conditions. For planetary, light pollution has zero effect, so you can observe right from your backyard in a downtown area. The most important thing is the stability of the air above. The better your seeing i.e. steadiness of the image, the larger the instrument I would install. The farther south you live, the larger the scope that will be most effective. If you can only afford a 6"or 7" instrument, don't despair that you will not see anything. I know some top planetary amateurs who regularly observe with those apertures and have seen amazing detail on the planets."

 

https://www.cloudyni...-telescope-r402

 

Jon Isaacs


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#9 Diego

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Posted 23 October 2020 - 06:49 AM

If I recall correctly, the "spokes" on Saturn were reported by Stephen O'meara before the Voyager 1 missions. I'm not sure what telescope he had at the time, but I know he uses a 4" refractor. So it makes no sense to rule out telescope capabilities by size.

Edited by Diego, 23 October 2020 - 06:51 AM.

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#10 Jon Isaacs

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Posted 23 October 2020 - 07:51 AM

I don't believe everything I read.

 

Yes.

 

In particular, that Jean Texereau actually said that it was of no use observing the planets with a scope less than 7 inches.  

 

Jon


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#11 Wildetelescope

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Posted 23 October 2020 - 09:50 AM

-John Texereau, paraphrased.  I read a book he wrote about his observing experiences.  I believe expanded, he meant that clear, verifiable visible features were better presented (especially so-called "transient" features) and more reliably recorded using scopes above 7 inch aperture.  He was also adamant that observations done in anything but pristine seeing were suspect.

I agree with Jon, more context is needed to understand the author's point.  While everyone knows that larger aperture and excellent seeing promotes the best experience for planets, I would not use that as a justification for NOT pointing my 80 mm telescope at Jupiter occasionally!  And if I waited only for the most pristine seeing conditions, I would look at a planet once a year.   I have had some remarkable moments with my son and a telescope of modest aperture looking at solar system objects.  Surely, I do not see the level of detail I once saw in a friends 10 inch Cat under an incredibly stable sky,(Dec 31, 2003 Ellicott city MD), but I still get a thrill when I can see the red spot or Cassini division through my 4 inch refractor.   I remember the excitement that my father had when he got to see Saturn through a friends 3 inch achromat, which was basically just an orange BB in a washer:-)  He talks about it to this day, 25 yrs later.

 

Finally, I would point out that Galileo changed how we see the physical world forever with a ~1 inch aperture refractor that would be put to shame by the most modest of dime store scopes available today.  A telescope is just a tool.  It is the observer and how they choose to use it that makes the results relevant.

 

Cheers!

 

JMD


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#12 BillP

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Posted 23 October 2020 - 11:35 AM

-John Texereau, paraphrased.  I read a book he wrote about his observing experiences.  I believe expanded, he meant that clear, verifiable visible features were better presented (especially so-called "transient" features) and more reliably recorded using scopes above 7 inch aperture.  He was also adamant that observations done in anything but pristine seeing were suspect.

If that is what he truly said, all I can say is lol.gif and rofl2.gif and oh yes looney.sml.gif

You should have seen the views I had last evening in the 81mm...simply amazing and mesmerizing!


Edited by BillP, 23 October 2020 - 11:38 AM.

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#13 Jaimo!

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Posted 23 October 2020 - 02:19 PM

If you are like me and have never heard of Jean Texereau...  as I am not a mirror grinder, follow the link.


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#14 vahe

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Posted 06 November 2020 - 11:29 AM

I don't believe everything I read.

I am also skeptical of all that is claimed here on the internet particularly comments along the lines “the best image of Saturn that I have ever seen” referring to the views in someones 4” achromat pointed at the ringed planet, yah right !!!, I have learned to read and move on.

.

Here is something that I do believe is accurate and believable, it is an article that appeared in S&T November 2018 page 52, “Best aperture for seeing the Planets” by Thomas Dobbins.

.

If you can I would recommend that you find and read this article, here is a clip from that two page article:

.
“Instruments with apertures smaller than 8 inches are certainly capable of providing very satisfying views, but they are less than optimal in terms of resolution and lack of image brightness required to reveal the muted pastel hues of many planetary markings. Based on five decades of observing through a vast array of telescopes , I’d venture to say that under excellent conditions, a 10 or 12 inch instrument of high quality is capable of revealing at least 75% of what can be seen on the Moon or brighter planets through even the largest Earth-based instruments.
The larger apertures required to see the remaining 25% involve rapidly diminishing marginal returns…………”

.

Vahe


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#15 Sketcher

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Posted 06 November 2020 - 12:40 PM

You know what they say about opinions . . .

 

A 1-inch telescope can show Jupiter's four largest moons, the planet's South Equatorial Belt and hint at the existence of a North Equatorial Belt:

 

Jupiter 1 inch 67x March 30 2019 2
 

A 1-inch telescope can show that Saturn is different and has "ears", or "handles", or a ring, or whatever:

 

Saturn 1 inch 67x March 30 2019 4

 

A 1-inch telescope can show that Venus undergoes phases along with corresponding changes in its apparent diameter:

 

Venus 1 inch aperture 19 Oct 2018 67x Sketcher   Text

 

Only a blind person would say: "A scope under 7 inches aperture is of no use observing planets."

 

On the other hand, it's not the telescope that does the observing.  It's sad and most unfortunate that some observers lack the ability to see and/or lack the ability to appreciate the sights that even the smallest of telescopes can reveal.

 

Is it just me who gets amazed and shocked when reading about new owners of 11-inch and 14.5-inch telescopes who have been unable to see some of the things that a 1-inch telescope is capable of showing?  In light of that, I guess it shouldn't be so surprising to read that someone feels that at least a 7-inch telescope is needed for planetary observation.

 

. . . just another case of the blind leading the blind.


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#16 arrrrgon

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Posted 06 November 2020 - 03:31 PM

I am also skeptical of all that is claimed here on the internet particularly comments along the lines “the best image of Saturn that I have ever seen” referring to the views in someones 4” achromat pointed at the ringed planet, yah right !!!, I have learned to read and move on.


The best view that person has seen isn't necessarily the best view you've ever seen. My 8" Dob has good planetary views, but my 60mm f/15.2 achromat shows amazing views of Jupiter. There's more detail and more color (not false color).

These are views done on the same night side by side with proper cooling and collimation. Maybe it's just how my eyes work, but while I can get a great view of Jupiter magnified much larger than my 60mm could ever hope for I still prefer the 60mm image.

Now obviously the 8" blows the 60mm away in every other way, but the 60mm holds it's own on planets.

#17 Astrojensen

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Posted 06 November 2020 - 03:33 PM

Whether a scope of under 7" is no use observing the planets really depends on what results we expect. If we want and expect consistently scientifically useful results, then yes, anything below 7" (or perhaps significantly larger) is not of much use today, since all the low-hanging fruit has since long been picked, but if what we want is personal entertainment and education, then anything goes, even a 1". 

 

And if personal education and entertainment is the focus, then aperture becomes less important and ease of use more important. 

 

 

Clear skies!

Thomas, Denmark


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#18 Astrojensen

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Posted 06 November 2020 - 03:41 PM

The best view that person has seen isn't necessarily the best view you've ever seen. My 8" Dob has good planetary views, but my 60mm f/15.2 achromat shows amazing views of Jupiter. There's more detail and more color (not false color).

These are views done on the same night side by side with proper cooling and collimation. Maybe it's just how my eyes work, but while I can get a great view of Jupiter magnified much larger than my 60mm could ever hope for I still prefer the 60mm image.

Now obviously the 8" blows the 60mm away in every other way, but the 60mm holds it's own on planets.

I'm sorry to say it, but your 8" must be absolute trash on the planets, otherwise I can't make sense of your post. My $200 6" f/8 completely outperforms my 4" ED on Jupiter (and also did so with a $4000 4" triplet apo I had on loan), not to mention anything smaller. The planetary images are incomparably richer in detail and color, especially Jupiter.  

 

 

Clear skies!

Thomas, Denmark 



#19 arrrrgon

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Posted 06 November 2020 - 04:13 PM

I'm sorry to say it, but your 8" must be absolute trash on the planets, otherwise I can't make sense of your post. My $200 6" f/8 completely outperforms my 4" ED on Jupiter (and also did so with a $4000 4" triplet apo I had on loan), not to mention anything smaller. The planetary images are incomparably richer in detail and color, especially Jupiter.


Clear skies!
Thomas, Denmark


It's not. It gives great views of the planets, and yet the view of Jupiter through the 60mm looks better to my eyes. This same 8" has shown me distant nebula and many other things. The 60mm also looks better than my 80ED on Jupiter. There's nothing wrong with any of the scopes. The 80 gives nice planetary views too though. I don't know how to explain it to anyone other than to say that to my eyes the view of Jupiter through this scope looks amazing. I tried a 90mm Mak and a 6" newt as well. All on the same night. Just sharing what I saw.

My wife really likes the view through the 8" on Jupiter though. It is a larger view. It has plenty of detail, but to my eyes the 60mm view just looks better.

#20 Rich (RLTYS)

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Posted 07 November 2020 - 04:45 PM

I have an origional Telvue Genesis 4" f5 Refractor which gave excellent views of the planets especially Jupiter and Saturn. waytogo.gif


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#21 grif 678

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Posted 07 November 2020 - 07:13 PM

I can see much more in a 4 inch scope, because I am able to use it more easily and readily, than a 7 inch, if I owned one. You can see more in a scope that you use more, especially the older you get.



#22 jrkirkham

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Posted 07 November 2020 - 10:50 PM

They always say that the best telescope is the one you use most. I once set aside about a year and a half with nothing more than a 50mm refractor and a 25mm eyepiece on a camera tripod. During that time I duplicated Galileo's experiments and tried to imagine what it would have been like to come up with some of his insights with no more gear than that and no modern understanding of astronomy. That time period was one of the best astronomy exercises that I have taken to date. It is probably second only to finding all the Messier objects. I enjoyed every minute and all my other gear stayed in storage during that time. Did that 50mm refractor offer views to compare with my C11? Of course not, but neither could the C11 give me  give me the insights that I got from that little scope. Even today there are times I would rather spend time with a little refractor.


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#23 E_Look

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Posted 08 November 2020 - 02:20 AM

There is a CNer, azure1961p, who has gotten marvelous observations of planets with a 6" scope.  I'm sure there are others here.  I'd say it would have more to do with the night's viewing conditions and skill of the observer, more than the absolute parameters of the hardware.


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#24 John Boudreau

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Posted 08 November 2020 - 03:40 AM

If I recall correctly, the "spokes" on Saturn were reported by Stephen O'meara before the Voyager 1 missions. I'm not sure what telescope he had at the time, but I know he uses a 4" refractor. So it makes no sense to rule out telescope capabilities by size.

Sorry I'm responding a bit on the late side--- The O'Meara 'spoke' observations were made with the 9" f/12 Alvan Clark at Harvard College Observatory in Cambridge, MA. As were his early 1980's observations of spots on Uranus that led to a reasonable estimate of the planet's rotation period.


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#25 mikemarotta

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Posted 17 November 2020 - 11:40 AM

Just to add... the 200-inch Hale is only the 19th largest reflector in the world. Might as well melt the glass into champagne flutes and celebrate the death of observational astronomy.

 

https://en.wikipedia...ting_telescopes

 

I suppose that it depends on what you mean by "science." It is true that with my 2-3/4 inch National Geographic refractor, I am not going to discover a new planet. But to say that you should not bother unless you are at some arbitrary professional level would put an end to every amateur activity on Earth (and in space: the ARRL launched its first satellite before AT&T did). Practicing science is what we do, whether anyone else benefits or not is secondary to the edification that derives from the activity.

 

 


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