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Cosmic Challenge: Barnard's Loop

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Cosmic Challenge:

Barnard's Loop


January 2017


Phil Harrington

This month's suggested aperture range

Naked eye


One of the greatest naked-eye challenges goading amateur astronomers around the world is trying to spot the elusive arc of nebulosity known as Barnard's Loop.  Cataloged officially as Sharpless 2-276, Barnard's Loop is a ghostly, 10°-wide semicircular bow of nebulosity that wraps around the eastern side of Orion, the Hunter.  In long exposure photographs, it bears the unmistakable resemblance to portions of the Veil Nebula supernova remnant in Cygnus.  Spotting it by eye stands as a monumental test for observers.

Above: Winter star map.

Credit: Star Watch by Phil Harrington


Above: Finder chart for this month's Cosmic Challenge.  

Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window

Although named for the renowned American astronomer Edward Emerson Barnard (1857
1923), who described the scene he captured on photographs made in October 1894 as a "great nebula extending in a curved form over the entire body of Orion," Barnard was not the first person to glimpse the Loop.  Records show that Barnard's Loop was discovered visually by Sir William Herschel.  Herschel published observations of 52 broad regions of the sky that he thought contained traces of nebulosity.  The region around Barnard's Loop is listed as Area 27 and is centered at Right Ascension 05h 48.3m, Declination +01° 09.9'.  Practicing an economy of words, Herschel simply described his 27th entry as "affected with milky nebulosity."

Few confirming observations were made of Herschels 52 nebulous regions, igniting a debate over their existence that raged in certain astronomical circles for more than a century.  While some of Herschel's 52 regions have subsequently been proven false, Barnard's images of Area #27 left little doubt about its existence.

Debate over Herschel's Area #27 continues to this day, but now, it revolves around seeing the Loop by eye.   Many amateurs have noted sections of the Loop through surprisingly small apertures, ranging in size from 50-mm binoculars to 3- to 5-inch telescopes.  But can Barnard's Loop be seen by eye alone?  It certainly is large enough, spanning the height of Orion's star-studded torso.  Is it too faint, or more correctly, too red for the human eye to detect?  The answer is "no;" it can and has been glimpsed without optical aid.  But there are a few caveats.

I have read many accounts of observers claiming to have seen Barnard's Loop by eye, but I suspect many of them are false.  That's not to say the observers are falsifying what they saw.  I don't doubt their honesty in the least.  But from their descriptions, I suspect that they did not see the real Loop, but rather a string of faint stars that follow very nearly the same path through Orion.  The False Loop is formed by 10 stars that shine between magnitude 4.5 and 5.  The illusion begins north of the Belt stars at Psi (Ψ) Orionis, and then hooks counterclockwise around the Belt, connecting the stars 33, 38, Omega (ω), 56, and 60 Orionis.  The False Loop then winds to the southwest, linking the faint stars SAO 132732, and 55, 49, and Upsilon (υ) Orionis as it curves between Orion's Sword and the stars Saiph and Rigel.  Although these stars are widely separated, as evidenced on the chart above, the brain tends to play tricks on us when we're not careful.  Rather than interpret the False Loop as a series of faint stars, our eye-brain system tends to fill in empty gaps to create a single image, especially at low light levels.  This optical illusion is caused by our psychological tendency to connect indistinct features into some sort of comprehensible whole, and is exactly why Percival Lowell saw straight canals crisscrossing Mars.

In order to see the real Barnard's Loop, several factors have to come together.  First, a clear, dark night free of any trace of moonlight, haze, and clouds is an absolute must.  Light pollution, especially in the direction of Orion, is also a no-no.  It is best to wait for Orion to be highest in the sky, to further remove any terrestrial interference.  You, the observer, should be seated or lying down; standing will only cause eye strain and interference.  The best solution would be to lie a chaise lounge tilted so that you are looking at Orion more or less straight on.  You also need to know the point where your eyes' peripheral vision is most sensitive.  Review the discussion in chapter 1 for further thoughts.

If you have them available, try narrowband and Hydrogen-Beta filters to improve image contrast.  If possible, hold identical filters in front of both eyes simultaneously to take advantage of binocular vision.  Some observers report good results with these, but Oxygen-III filters seem to offer little benefit.

Start with the Loop's brightest segment, which lies just south of 56 Orionis and ends just west of SAO 132732.  If you spot that segment successfully, see if you can extend it toward the region in between 56 and 51 Orionis.  Try staring toward the Belt stars, while focusing your peripheral vision toward SAO 132732.

Okay, take a breath.  Unfortunately, the southern half of Barnard's Loop is quite a bit fainter than the northern half.  To spot the segment lying between Saiph (Kappa [κ] Orionis) and Rigel (Beta [β] Orionis) try blocking both stars with your fingers using the "V for Victory" sign.  Doing so just might make you victorious.

Above: Barnard's Loop. Credit: Kevin Dixon


Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my web site or post to this month's discussion forum.

Until next month, remember that half of the fun is the thrill of the chase.  Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2017 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


  • Mr. Bill, R.bak, okiestarman56 and 1 other like this


Enjoyed this month's article Phil. Nicely done. 

    • PhilH likes this

Hi, Phil et al, Thanx for the intriguing article/challenge! My skies are quite good, occasionally superior, but never exceptional. I can "see" such objects as the N American Nebl, Lagoon, etc. naked eye... but have convinced myself that it is actually the associated stars, and not the red Ha itself that I am enjoying. And I have never visually detected overt red/pink (Ha), that others claim, in M42, even with huge RF Dob. UHC, Hb and OIII filters DO show many/most emission nebl nicely, but those bands/lines would be (if anything) greenish-blue, not red. I have since "cheated" using Gen3 NV 1x True Binos + Ha narrow band filters. The H-alpha sky then Lights Up at 1x scan and the "naked eye" feeling is Intense! All the familiars (N Am, gamma Cyg, M42, Barnard's Loop, California, Rosette, etc.) are blazingly obvious. I'm leaning toward thinking true naked eye Barnard's Loop may be stars and not true perception of the emission itself. It's SO tempting to "see" below-threshold, when we preemptively know what is there. Reminds me of the Martian Canals... where some experts would see (and sketch) them... yet others would try and try and come up empty-handed.  Tom

    • PhilH and Kimbo_2112 like this

One night on Mt. Pinos (2550m, 8350') here in SoCal, skies of 21.4mpsas, a friend and I saw nearly the entirety of Barnard's loop from the shoulder around to nearly Rigel

by mounting a Lumicon H-Beta filter in a short extension tube and holding it up to the eye in a way that blocked all peripheral light.

That high altitude site has, often, ultra-transparent air, and this was one of those nights.

On a similar night we saw the Veil Nebula with the Naked eye and O-III filter, but that is a different story.

    • Dave Mitsky, mwedel, Tarzanrock and 1 other like this

living in Hudson valley 50 mile north of  NYC naked eye view of Barnards loop out of the question 


however I do the next best thing is night vision with Ha filter "its real time" and I can pan sky and see all kinds of gas clouds up there


i like to try that h-beta trick up in dark sky area thanks for that tip


Dave Mitsky
Jan 06 2017 08:43 PM

Enjoyed this month's article Phil. Nicely done. 



Dave Mitsky

Jan 07 2017 02:58 PM

would 2.3x40 Blue Planet Optics or similar Vixen or Nikon TC2E or TC3E hand made binos make it easier to see Barnards Loop?

The image would not be any brighter than the naked eye and the magnification would be higher.

I doubt it would be any easier, but it might be the same as naked eye.  You'd need two full-aperture H-Beta filters, though,

and that would be expensive.

Jan 08 2017 02:40 AM

is it posslible to see Barnards loop using a UHC filter? the H-beta line  is included (right?), or is it too dim or something? 

Barnard's Loop is like the nebula behind the Horsehead--very faint--and maximum contrast is desirable (which means the narrowest bandwidth)

A UHC filter that passes the H-Beta line might work, but the contrast would be less than a pure H-Beta filter.

It's certainly worth trying.

Use some form of light-blocking holder for the filter (maybe your thumb and index finger around the filter with the hand touching your eyebrow and cheek bone)

or a short barrel extender.  And make sure you are completely dark adapted (45 minutes outside away from lights) and do not spend a lot of time looking at the sky before you try.

Also, wait until Orion is near the N-S meridian and at its highest altitude to improve the odds of success.


These days, some UHC-type filters are narrower than some H-Beta filters, so it will depend a lot on the filter used.

You want a high (>90%) transmission on the H-Beta line, and <26nm in bandwidth.

There aren't many UHC filters that meet those requirements.

    • Kimbo_2112 likes this

I don't think I have ever been under dark enough skies to see Barnard's Loop unaided, but as some other folks have commented, a good Gen3 Night Vision device makes it (and other H-alpha nebula) pop out, clear as day, even from urban/suburban skies.  Here are some a handheld shots taken with my iPhone held up to the eyepiece of my Mod3 night vision device, with a 7nm h-alpha filter.  You can see M42/M43, Barnard's Loop, Rosette, Horsehead and Flame, and the Angelfish nebula, all within this 40 degree field.  It's marvelous and lovely!


Screen Shot 2016-12-28 at 11.54.02 PM.png
Screen Shot 2016-12-28 at 11.52.29 PM.png
    • Jeff Morgan, nicknacknock, Luis Gabriel and 2 others like this

I was interested to read this because of the revelation (to me) about the "False Loop."   


Even with some of the best image intensifiers available to civilians,  Barnard's loop is not a slam dunk. From my own home 3.5 miles from down town Austin Tx, I have only glimpsed the brighter condensation on he east side.



Peter and I recently did a short session at Mansfield Dam about 15 miles form down town Austin Tx and while the skies are much darker than my home they are still not particularly dark at all and on Saturday night, they were only fair by that locations standards.  Even with Mag 4.5 stars, I could detect no sign of the loop.  There was a very thin haze and a 70% moon and those conspired to deny me even a hint of Barnard's Loop.


I have absolutely seen Barnard's from that same location in the past on a night of better transparency, and while most of its lenght was visible, it did not "jump" out of the background.


Under dark and dry skies, it is a fantastic sight.  The amount of extension is considerable and is not much different than shown in the picture in the article.  With very dark skies and high transparency it becomes one of the most magnificent objects in a sky that is crowded with nearby bright nebula.  In this part of the sky, nothing rivals it.


To the naked eye with no filters, even in what is considered the darkest sky left in the United States it is totally invisible.   I did not have the recommended filters for visual use, but I would suspect that any report that suggest it can be seen with the naked eye and no filter would likely be (as you suggest in the article) the False Nebula. 


It is though a staggeringly beautiful object. 

I might mention that they sky in this region is awash with what I believe may be Integrated Flux Nebula (IFN).  Mel Bartels has reported on seeing IFN visually in his very small Richest Field Reflector, and after seeing this region using image intensifiers, I have no doubt that his report is correct.  The entire corridor of the Milky Way around this region shows a very large scale mottling of nebulosity.   I have only seen it once from southwest Texas on one night of Mag 6.5 seeing,  but it was unmistakable.  

We are surrounded by giant gas clouds all along the span of the Milky Way, but Barnards Loop and Barnards Loop is one of best of these to see, but even with high end night vision, the results can be extremly varied and just as with telescopic and naked eye viewing, the darker and more transparent the sky the better chance to see it or the better the view will be.

I have seen the brighter sections of the loop between Alnitak and Betelgeuse from my heavily light polluted home in the Philadelphia suburbs with a 50mm guide scope equipped with a NVD Micro image intensifier and 7nm Ha filter.


Both the Flame and Horsehead nebula are easier to see and stand out more apparently using the same equipment and on the same night.



Agreed that the visibility of Barnard's Loop even with night vision is very dependent on viewing conditions.

Phillip Creed
Jan 11 2017 04:41 PM

I got a good portion of the arc, particularly the section near NGC 2112, with the naked-eye without filters, but only under the most extraordinary viewing conditions.  In the late winters of 2005 and 2008, I was in Big Bend National Park around 29°N latitude, placing that portion of the nebula more than 60° above the horizon.  The air was incredibly transparent and the skies were the very definition of Bortle Class 1.  As dark as dark gets.  The Horsehead Nebula and the Medusa Nebula (Abell 21) were visible in a set of unfiltered 25x100 binoculars.

I have not been able to repeat that feat from any site other than Big Bend, even under the best of conditions in places like Cherry Springs or Calhoun County Park.  I could, though, readily see portions of the nebula from a green-zone site with unfiltered 15x70 binoculars on a cold, crisp winter's night.


Clear Skies,


This is fantasy, but imagine a capsule/space station with superb fused silica MARC coated window. And you (I) am an astronaut, totally dark-adapted, relaxed, oxygenized and have binos etc. available. What might that look like?! Does the Space Station have that view and someone experienced in looking? If you're on the dark side of the earth and station with no lit structure blasting in... Hmmm  Tom

David Knisely
Jan 13 2017 03:31 AM

is it posslible to see Barnards loop using a UHC filter? the H-beta line  is included (right?), or is it too dim or something? 

Yes, it is possible.  In fact, my very first sighting of at least part of the loop came way back around 1981 when I got my first look at the new Lumicon UHC filter a friend of mine had.  I held it up to my eye and almost immediately noted the "puff ball" of the Rosette, but when I glanced down towards Orion, I noted a faint arc above and to the left of Zeta that curved down to the east past the star and then ran a bit farther to the south.  I was stunned when I realized what it was, and immediately brought it to the attention of my friend, who then duplicated the observation.  Since then, the H-Beta has provided me a somewhat better view of more of Barnard's loop than the UHC did, but the UHC was the one that first allowed me a glimpse at what I had previously determined to be an "impossible" visual observation.  Clear skies to you.

Jan 19 2017 07:07 AM

thank you for the description of the "false loop"


I thought that I saw it once, but with my LP and eyesight,

this seemed unlikely


now I know I have seen the "false loop"



Jeff Morgan
Jan 21 2017 10:16 AM

Walter Scott Houston wrote of seeing Barnard's Loop, the Rosette, and California nebulas with naked eye and nebula filter. I don't recall the issue though.


Unfortunately, searching for it is problematic since the the Sky & Telescope DVD collection it no longer works with Flash.


Perhaps someone here recalls the date of the article?

Walter Scott Houston wrote of seeing Barnard's Loop, the Rosette, and California nebulas with naked eye and nebula filter. I don't recall the issue though.


Unfortunately, searching for it is problematic since the the Sky & Telescope DVD collection it no longer works with Flash.


Perhaps someone here recalls the date of the article?

I have heard of people doing it visually, but I am skeptical that they could see much more than the narrower and brighter regions.


Even with an image intensifier, it takes fairly clear skies to see it to much of it's full extent.


I too saw it from near Big Bend using an image intensifier and it was simply out of this world.  To the image intensifier under dark and clear skies, it is highly detailed.

The entire region is filled with nebulosity (some of it I think Integrated Flux Nebula) and in a 40 degree true field, it is a mind bending peek at the real nature of the Milky Way.  It is dominated by very large scale dust and gas cloud that make the largest of stars seem puny by comparison. 


Consider that Barnard's loop is 500 light years away and 300 light years across at its widest, and one can quickly conclude that it is one of the most majestic structures visible to us in the Milky Way.   Entire solar systems are minute by comparison. 

Barnard's Loop seems far more likely to be at a greater distance:

"Recent estimates place it at a distance of either 159 pc (518 light years) or 440 pc (1434 ly) giving it dimensions of either about 100 or 300 ly across respectively. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including AE Aurigae, Mu Columbae and 53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova."

The Wiki article goes on to say that the stars of the Orion Nebula are believed to be the source of ionization, implying the greater distance is the correct one, since the Orion Nebula is at the farther distance.


When I and a friend saw it, we tracked the part north of the belt quite easily, but we were surprised to see it almost extend to Rigel on its southern end.

[the H-beta filter, attached to a short barrel extender, was held up to the eye]

Since that was at high altitude on a transparent night, I'm convinced altitude is a big asset to observing faint stuff.

We didn't see any other faint nebula covering other parts of Orion.  The Lambda Orionis patch, for example, was not visible.

It must have a lower surface brightness or respond to a different filter.

Lots of great discussion here!  I'm glad my article spurred it on!


Jeff, your post prompted me to hunt down an article by Scotty Houston, to see his thoughts about Barnard's Loop.  Like you, however, my CD collection didn't work either because of Flash.  So, now I had two missions.


First, to the Flash issue, a search on CN found this thread in another forum: http://www.cloudynig...et-not-working/


A third of the way down, Richard (aka Carl Kolchak) posted the solution.  You need to roll back to Flash Player version  I did this morning and life is good again.  Adobe has a video tutorial about rolling back to earlier versions.  You'll find it here: https://forums.adobe.../thread/1022066


Once I got that resolved, I found what I believe is Scotty's first mention of the Loop, from the January 1987 issue, page 116.  He recalls how he saw it naked eye from Joshua Tree National Park, using a UHC filter with a dark cloth draped over his head.  He also saw the California Nebula with the same set-up.

    • Jeff Morgan and nicknacknock like this

Odd.  I have the complete set of S&T magazines going all the way back,

and have Windws 10 Pro on a desktop computer with all the latest drivers and have absolutely

no problem reading any S&T magazine on any disc.

Jeff Morgan
Jan 26 2017 12:22 AM

A third of the way down, Richard (aka Carl Kolchak) posted the solution.  You need to roll back to Flash Player version  I did this morning and life is good again.  Adobe has a video tutorial about rolling back to earlier versions.  You'll find it here: https://forums.adobe.../thread/1022066

:waytogo:  You the man!


I always knew about the northern portion, but M42/43 always have drawn my concentration in the southern half of the constellation. Your article motivated me to track down the southern end of the loop for the first time tonight. I was observing from my suburban skies (Bortle 5 perhaps) using my NV monocular and 135mm telephoto lens (about 3x). Sure enough, it does go to Rigel where it appears to feather out into regular space, hard to be sure with just a 7nm filter.

Jeff Morgan
Jan 26 2017 02:49 PM

FYI: Sean Walker of Sky & Tel has just published a fix for the Flash issue over on the Astronomy Software forum.

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