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Can you really see +7 magnitude stars with your eyes in bortle 1 or 2 skies?

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#1 DAG792

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Posted 09 April 2020 - 12:10 AM

This fact comes up quite a lot on the internet. Recently, I was reading a Sky and Telescope magazine article, and it stated that Stephen o Meara was able to see better than 7, and on some occasions even 8 magnitude stars with his naked eye alone. Is this possible? I find it very hard to believe because I've observed from Bortle 3-4 sites on a couple of occasions, and the best I could do was about mag 6.3 (with considerable effort). I am by no means an expert, and have only been involved in amateur astronomy for the best part of 2 years, but still, I know most of the techniques like dark-adaptation, averted vision and I still couldn't do any better. I have excellent eyesight (better than 6/4 in my right eye) but still, such a feat seems impossible to me. I mean no disrespect to o Meara, however is there anyone here who has observed from perfect (Bortle 1 or 2) sites and was able to replicate o Meara's feat? If not, why don't you give the faintest magnitude you've ever seen. Just a curious question on my part...

 

Any replies are welcome.



#2 AstroBrett

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Posted 09 April 2020 - 12:43 AM

O'Meara is legendary for the exceptional sensitivity of his exceptional eyesight. So, I'd rephrase your question as "Is it possible for one of the most experienced observers in the world with exceptional visual acuity to see something five to six times fainter than the average observer?"  I'd bet that it is, although I'll be the first to say, I can't come close to his performance under mag 21.5 / Bortle2 skies after 50+ years of observing.  But that has absolutely nothing to do with the question of whether Stephen O'Meara can. 

 

Brett    


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#3 Astrojensen

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Posted 09 April 2020 - 01:45 AM

I've seen down to mag 7.1 in B3 skies on rare occasions, so it's definitely doable, but how difficult it is varies tremendously from person to person. 

 

 

Clear skies!
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#4 TOMDEY

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Posted 09 April 2020 - 01:53 AM

Yes! Giovanni Schiaparelli could see mag 7+ and Percival Lowell could see mag 8+.    Tom


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#5 JOEinCO

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Posted 09 April 2020 - 02:57 AM

Yes!.....and Percival Lowell could see mag 8+

Lowell could see a lot of things others couldn't. lol.gif lol.gif lol.gif 


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#6 siriusandthepup

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Posted 09 April 2020 - 04:31 AM

A small group of us did a limiting mag test using the stars in the bowl of the little dipper at TSP many moons ago. My friends girlfriend made it to mag 7.4, I only made it to 7.2. She was a regular observer with us - not a random person. She understood averted vision. The bowl was in the upward position - so not terribly low to the horizon. (edit: Texas Star Party is held at the Prude Ranch at 5000ft elevation under the protection of McDonald observatory's county wide light pollution controls)

 

I have been in much darker skies on rare occasion where (with out any test) I'm sure I could reach another 1/2 magnitude. (edit: northwest New Mexico, about 50/60 miles north of Silver City very isolated and unpopulated area at 8000ft elevation)

 

Use stars at the zenith on the darkest night for the win. Very very dependent on local conditions. The bowl stars of Corona Borealis is a prime candidate at the proper time for us northern hemisphere peeps.

 

waytogo.gif


Edited by siriusandthepup, 09 April 2020 - 09:23 AM.

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#7 Jon Isaacs

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Posted 09 April 2020 - 04:37 AM

Can you really see +7 magnitude stars with your eyes in bortle 1 or 2 skies?

 

I can't. 

 

Some of the other things I have never done:

 

- Run a 4 minute mile.

 

- thrown a baseball 100 mph.

 

- Bench pressed 600 lbs.

 

A Bortle 3 could be anywhere from 21.3-21.5 mpsas, (measured, not from a map), a Bortle 4 site could be anywhere from 20.4 to 21.3.

 

Using Mel Bartels SQM versus NELM calculator, a Nelm of 6.3 translates to 21.3 mpsas so it seems you are pretty much right on target.

 

https://www.bbastrod...Mconverter.html

 

Jon


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#8 Tony Flanders

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Posted 09 April 2020 - 05:10 AM

The faintest star that I have knowingly seen was magnitude 6.9. But my acuity is not very good. For instance, I can't split Epsilon Lyrae into two components with my unaided eyes, something that many people can do fairly easily.

 

Incidentally, my ability to see faint stars seems to top out around Bortle 3; increasing darkness beyond that does not increase the number of stars that I can see. The same is definitely not true for faint fuzzies; the Milky Way appears far more detailed to me at Bortle 1 than at Bortle 3.


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#9 bunyon

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Posted 09 April 2020 - 05:25 AM

I don't know Stephen O'Meara so I don't know. Can he still see such faint stars? He was young (for an observer) when he made many of his famous observations. To use Jon's analogy, Roger Bannister couldn't have run a 4 minute mile in his 60s and Nolan Ryan can no longer throw 100 mph. 



#10 BradFran

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Posted 09 April 2020 - 05:44 AM

Yup, 7.5 naked eye from Bortle 1-2 and 8,000 feet... many years ago. I've observed with people who can see fainter in the telescope than I can. I believe them. I think O'Meara is being accurate. He probably has a biological advantage and much, much more experience as well as practice than the average bear. Seeing, transparency and darkness also play large roles. Looking at Jupiter will put your night vision off by quite a margin. When it gets really dark, the milky way casts shadows. The human eye can be very sensitive.


Edited by BradFran, 09 April 2020 - 05:58 AM.

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#11 Second Time Around

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Posted 09 April 2020 - 06:09 AM

I can't. 

 

Some of the other things I have never done:

 

- Run a 4 minute mile.

 

Using Mel Bartels SQM versus NELM calculator, a Nelm of 6.3 translates to 21.3 mpsas so it seems you are pretty much right on target.

 

https://www.bbastrod...Mconverter.html

 

Jon

Thanks for that useful link, Jon!  According to that, at my 20.8 skies my NELM would be 6.0.  However the best I've got would be about 5.5. I can think of two reasons for this.

 

Firstly it's not just how sharp one's eyes are that determines NELM.  My eyes are 6/4 (=US 20/12.5), so much sharper than average. Hopefully that will help.

 

However, my dark adapted pupil size is only 4.5mm, so quite a bit less than average. I assume this will make a significant difference.

 

Secondly, the 20.8 figure may be optimistic.  As far as I can determine, that's based on the 2015 World Atlas data; the VIIRS 2019 figure isn't as good, so presumably light pollution has got worse here.

 

Thoughts anyone?



#12 harbinjer

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Posted 09 April 2020 - 09:44 AM

Yes, the 4.5mm pupil size will make a big difference. I can't confirm but I recall reading that O'Meara's pupils open up to about 8mm. That's 100²mm vs 31²mm for your 4.5mm pupils. I'd say you're doing fine.

 

I'm bad at estimating magnitudes, but I have seen Milky Way shadows, from the Nebraska Star Party.

 

I would also add that seeing and transparency really make a noticeable difference in really dark skies. If those are ideal, I'm sure 7+ is possible.


Edited by harbinjer, 09 April 2020 - 09:48 AM.

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#13 epee

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Posted 09 April 2020 - 12:39 PM

Ted Williams stated that he could almost count the stitches on a baseball pitched to him; his batting average backed-up his claim. Chuck Yeager could spot enemy fights and cll out their position several seconds before his squadron mates looking in the same area. A top shooter of the Depression Era (forget his name) could read the title of a 78 RPM record while it was spinning.

 

I think 20/10 was the best vision ever recorded. Couple that with good night vision, and clear dark skies at elevation and 7-8 magnitude seems doable.


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#14 smithrrlyr

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Posted 09 April 2020 - 12:49 PM

In 1903, Heber D. Curtis published an interesting paper on the naked eye limiting magnitude in the Lick Observatory Bulletin (vol. 2,
p. 67 -- available through NASA/ADS).  The magnitude system employed was of course not Johnson V, but visual magnitudes of the day weren't bad for brighter stars. Curtis was then relatively young, and he describes his attempts to see faint stars with his unaided eye, taking care to exclude scattered light from his vision. His limit seems to have been around mag 8.3.  Of course, light pollution was apparently not a problem then at the Lick site. This seems to be consistent with O'Meara's limit.  Curtis gives a nice description of his approach in the paper.


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#15 Tom Polakis

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Posted 09 April 2020 - 05:20 PM

Way back in 1999, I filed a report on a visual-observers group, Amastro.  My friend Bernie Sanden and I did naked-eye limiting magnitude tests from a dark site at 5300 feet elevation in the southeast corner of Arizona.

 

Executive summary for long post below: we described the stars we were seeing in Pegasus without looking at a chart, while the other person "catalogued" it.  I was able to see mag. 7.4, but not 7.7.  Bernie, who has great visual acuity, reached magnitude 8.5.  As Tony Flanders mentioned above, visual acuity differs from seeing faint detail in diffuse objects, where Bernie and I were pretty similar.  I'd sort of like to repeat the test 21 years later, but I'm not sure I want to know the answer.

 

Here's the post.

 

---

 

I recently spent three nights at Sunglow Ranch in Southern Arizona.  The
site lies in the western foothills of the Chiricahua Mountains at an
elevation of 5300 feet.  Since sleeping in until noon was so easy there,
these were complete dusk-to-dawn observing sessions, with only a couple
brief naps each night.  Since the Arizona monsoon ended in September,
predicting cloudiness has been a no-brainer; there simply haven't been any!
Transparency was excellent on 2 1/2 of the 3 nights, while seeing was,
well, sub-five-arcsecond most of the time.

 

Among many spontaneous projects that arose during these long October
evenings was determining the limiting magnitude at this dark site.  The
magnitudes are "V" values from the Hipparcos catalogue, displayed on
Megastar on my nearby laptop computer.  My observing partner Bernie Sanden
consistently has a half-manitude on me, so after I discovered my limit, I
quizzed him.

 

We used the equilateral triangle of stars formed by eta, beta, and mu
Pegasi to guide our way to the the test stars.  I quickly developed a good
feel for the difficulty of seeing each half-magnitude step further down the
scale.  It bcame immediately apparent that this was well beyond the coveted
6.5-magnitude sky.  I found those stars to be easy with direct vision.
7th-magnitude stars were not so easy, but with some patience became
visible.  Very near my limit were HIP 113005 and 113063, both listed as
magnitude 7.4.  I could hold these stars with averted vision most of the
time.  I hit the wall at HIP 113092, which lies 10' west of a slightly
brighter star.  It has a Hipparcos V magnitude of 7.7.

 

Next Bernie came over to once again demonstrate just how dependent these
magnitude limits are on the observer.  While I stared at the screen, I had
him describe the positions of these stars.  He was able to see HIP 114833
and 114832, magnitudes 8.4 and 8.3, respectively.  Then he went on to
mention HIP 113481 and 113486, which are 8.0- and 8.5-magnitude stars.
After a long break away from the computer screen, I was happy to learn that
my limit had not changed.

 

This experience left me impressed that an observer could see so deep with
unaided vision.  We went on to easily spot M15 and M2.  Perhaps the
naked-eye Messier Marathon will be the next big thing in amateur observing.


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#16 Jon Isaacs

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Posted 09 April 2020 - 05:31 PM

I'd sort of like to repeat the test 21 years later, but I'm not sure I want to know the answer.

 

 

Tom:

 

I am not sure I want to the answer either.  :)

 

Do you remember Jeff Medkeff?  

 

jon



#17 Cotts

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Posted 09 April 2020 - 11:09 PM

There really must be something wrong with me...  At Texas S.P. And Okie Tex, both Bortle 1 sites I have never, ever cracked the 6.0 barrier.  I've nearly 60 years in the hobby and know all about averted vision, wearing sunglasses all day before observing....all that stuff....

 

At those sites M13 is at the absolute edge of my averted vision capability -and even that is a 50% frequency..  M33 has always eluded me...

 

I have tried the “count all the stars inside the Great Square of Pegasus” thing, the circles of ever fainter stars around Polaris and sketching a random area of sky within a recognizable triangle or trapezoid...  

 

Mag 6.0 is my record.

 

When I hear of people doing 7.0, 7.5, 8.0 I just have to consider my pretty good acuity and let it go at that...

 

8.5????

 

Dave


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#18 siriusandthepup

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Posted 10 April 2020 - 12:51 AM

 

There really must be something wrong with me...

Dave, I suspect that you have the same thing I have - old age.

 

One thing I learned when I got my cataract lens replacement surgery two years ago is how much unnoticed degradation had occurred during my lifetime.

 

After the lens replacement everything was much brighter and more colorful. When I commented to the Dr. about this - he said that "Now you can see like when you were young". We don't even realize the loss over the years - it's so gradual. NOT the cataracts I'm talking about, but the gradual yellowing of the lens. You get to our age and it's just like wearing sunglasses. Going for limiting magnitude with your sunglasses on is kinda non-optimum.

 

I need to redo my limiting magnitude tests next time I get to a dark sky to reestablish my new limiting magnitude. My 7.2 at TSP was done back in my 40's - already sliding down the age impairment pole.

 

Speaking of sunglasses - I never used to wear 'em because I was comfortable without them. NOW - I gotta have 'em on sunny days to drive - Too bright!!

 

YMMV


Edited by siriusandthepup, 10 April 2020 - 12:52 AM.

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#19 birger

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Posted 10 April 2020 - 02:35 AM

I've seen a 6.1 star at a Bortle 3-4 site (averted vision), but I've also seen a 5.7 star from outside my home (Bortle 5 skies). I can't remember the conditions during the visit to the Bortle 3-4 sky, but I remember visiting a Bortle 2 sky during bad conditions, and I was barely able to see the Milky Way!



#20 Tony Flanders

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Posted 10 April 2020 - 06:41 AM

Yes, the 4.5mm pupil size will make a big difference.


I vaguely remember a study that found little or no correlation between pupil size and limiting stellar magnitude.

My guess is that the biggest asset that Steve O'Meara has is exceptionally acuity rather than wide pupils. He was, after all, famous for his planetary observations long before he got into deep sky.

I have lousy visual acuity even when my pupils are fully stopped down. Many people have good acuity with stopped-down pupils but poor acuity when their pupils are wide open. Steve O'Meara seems like one of the lucky few with good acuity regardless of how wide his pupils are.


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#21 Cotts

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Posted 10 April 2020 - 11:21 AM

Dave, I suspect that you have the same thing I have - old age.

 

One thing I learned when I got my cataract lens replacement surgery two years ago is how much unnoticed degradation had occurred during my lifetime.

 

After the lens replacement everything was much brighter and more colorful. When I commented to the Dr. about this - he said that "Now you can see like when you were young". We don't even realize the loss over the years - it's so gradual. NOT the cataracts I'm talking about, but the gradual yellowing of the lens. You get to our age and it's just like wearing sunglasses. Going for limiting magnitude with your sunglasses on is kinda non-optimum.

 

I need to redo my limiting magnitude tests next time I get to a dark sky to reestablish my new limiting magnitude. My 7.2 at TSP was done back in my 40's - already sliding down the age impairment pole.

 

Speaking of sunglasses - I never used to wear 'em because I was comfortable without them. NOW - I gotta have 'em on sunny days to drive - Too bright!!

 

YMMV

I should have mentioned.  My 6.0 'record' is AFTER I had full lens replacements in both eyes in 2016.... 

 

My acuity got a lot better because the toric lenses pretty much eliminated my rather severe astigmatism.....

 

Dave



#22 Starman1

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Posted 10 April 2020 - 02:25 PM

This fact comes up quite a lot on the internet. Recently, I was reading a Sky and Telescope magazine article, and it stated that Stephen o Meara was able to see better than 7, and on some occasions even 8 magnitude stars with his naked eye alone. Is this possible? I find it very hard to believe because I've observed from Bortle 3-4 sites on a couple of occasions, and the best I could do was about mag 6.3 (with considerable effort). I am by no means an expert, and have only been involved in amateur astronomy for the best part of 2 years, but still, I know most of the techniques like dark-adaptation, averted vision and I still couldn't do any better. I have excellent eyesight (better than 6/4 in my right eye) but still, such a feat seems impossible to me. I mean no disrespect to o Meara, however is there anyone here who has observed from perfect (Bortle 1 or 2) sites and was able to replicate o Meara's feat? If not, why don't you give the faintest magnitude you've ever seen. Just a curious question on my part...

 

Any replies are welcome.

It would be possible IF:

--your eyes have large dilated nighttime pupils

--you have exceptional acuity, like perhaps 20/10 vision with zero astigmatism

--the seeing is exceptionally good

I have tried using the AAVSO charts in select areas to see how deep I can get, and my own best is around 6.9.  That is the limit of my acuity, and I am 20/15 with glasses on.

 

If I back out the very faintest star I've ever seen with averted vision in the scope to a naked eye figure, I should be able to see magnitude 7.

Even using the Schaefer-derived limiting telescope magnitude calculators, I should not be able to see deeper than magnitude 7.4 under completely ideal conditions (high altitude, perfect seeing, ultra high transparency, star at the zenith with a blue-white spectrum).  Seeing stars fainter than that would be achieving a limit in the scope far beyond what is thought theoretically possible.

I've heard of people seeing M81 with the naked eye.  I'm not sure I really believe it.

 

Barbara Wilson reportedly reached magnitude 18.6 with a 20" scope at the Texas Star Party, and that was considered to be quite a feat, but that is about the same as seeing magnitude 7.1 with the naked eye.

So I'm not sure I believe all I've read on the internet.


Edited by Starman1, 10 April 2020 - 05:21 PM.

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#23 Jon Isaacs

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Posted 10 April 2020 - 03:04 PM

Barbara Wilson reportedly reached magnitude 18.6 with a 20" scope at the Texas Star Party, and that was considered to be quite a feat, but that is about the same as seeing magnitude 7.1 with the naked eye.

 

 

Barbara Wilson, Tom Polakis and others are those 4 minute milers..   I am just happy to get around the track without fainting.

 

Jon


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#24 BrooksObs

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Posted 10 April 2020 - 03:09 PM

As the creator of the widely used Dark Sky Scale I can report that during the 1970's when my backyard skies were consistently a Bortle class 1-2 on any clear and moonless night, I could detect stars of 7.4 to 7.6 on every occasion using my unaided eyes. My personal best, IIRC, was a +7.9 many years ago while on Nantucket Island for a meeting.  I might add mention that there is a star immediately adjacent to the well known variable R CrB that is well established to be of magnitude +7.4 visual that I have employed for decades to establish the quality of darkness at various observing sites. Providing it is well placed in the sky and the variable star is in its faint state, up to the earlier 2010's I could always detect it using care and averted vision, given that the site was reasonably dark.

 

Incidentally, some years ago Barbara Wilson, my old friend Steve O'Meara, and I went head-to-head in determining our telescopic magnitude limits with Barbara's 20" at TSP. We employed stars of a very precisely established "v" magnitude field in Cancer. All three of us reached the exact same limit which was in the 18's that night, IIRC. None of us has ever claimed to possess exceptional vision, only many years as serious visual observers of countless faint objects. Many other of my AAVSO colleagues over the years have done similarly well.

 

BrooksObs


Edited by BrooksObs, 10 April 2020 - 03:14 PM.

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#25 Starman1

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Posted 10 April 2020 - 05:25 PM

I guess there are some people who, when the exit pupil gets smaller, see a decreasing limit on stars compared to what they see with the naked eye.

Like John above, for example, because a 20" should see past magnitude 19 if the naked eye can see 7.4 - 7.6.

More limited seeing at high powers could be to blame for that.

 

For me, it's about the same, i.e. the increase in light grasp figures out to nearly exactly the magnitude gain in the scope.

If I add the gain of the scope to the naked eye view, I can derive my telescopic limit fairly closely.

 

And, with others, their telescopic limit derives a naked eye magnitude quite a bit fainter than they can see naked eye.

The ostensible reason is poor acuity when the whole pupil is used.  I suspect this is fairly common.

Also, contrast for stars should improve with magnification, allowing the faintest stars to be seen at high powers and small exit pupils,

unless seeing is compromised at higher powers.

 

I suspect a lot of that has to do with astigmatism, clarity of the lens, corneal issues like "map" or "fingerprint" lines, etc.

And, perhaps, the resolution and sensitivity of the retina itself.

 

What that says is that there may not be a good correlation between naked eye limiting magnitude and telescopic limiting magnitude,

for a variety of reasons.

 

One thing is for certain though--the range of naked eye limits among observers is quite large, and has a lot to do with the acuity of vision in the observers.


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