"Horsehead" Nebula (B-33), photographed in 1989 by Ryan Wood
HORSEHEAD NONSENSE -- AND SENSE
an Article by Steve Waldee
The other night I whiled away some time looking at a certain forum, and happened to notice some posts about the Horsehead nebula. I could identify the website and specific thread, but I'd rather not be too critical of my fellow amateurs by name, since not everybody has done a specific intensive study of the object. Three of my associates and I, back in 1989/90, did an extensive research project which ultimately lead to the modern recognition and re-publication of the fact that Mrs. Williamina Fleming had first identified -- discovered, if you will -- the Horsehead on a picture taken at Harvard, and photographer William H. Pickering had immediately concluded that it was a dark nebula. This happened in 1888, and the realization of it has slowly made its way into the literature, prompted by Dr. Martha Hazen's talk in 1990 at the convention of the Astronomical Society of the Pacific, incorporating my research findings that she corroborated from the historical documents and photographs at Harvard. In addition, my amateur observing associates and I studied the Horsehead visually -- over more than two dozen observing sessions -- with a variety of telescopes, ranging from the most primitive, old, "junky" scopes, to premium custom-made and world-class instruments.
This study involved some limited use of controls to insure a fair chance that we were comparing apples to apples, and not oranges. We used a very good but arguably not 'near-perfect' site, which is not rated at the highest Bortle value for sky darkness. It was at a fairly high altitude of 3,400 feet; but not the highest elevation in our local region of the SF bay area (being 800 feet lower than Lick Observatory, and some 1600 feet below the site in the Ventana Wilderness where our friend Chuck Vaughn did his fabulous color astrophotos in the 1980s and 90s.) I planned the test, collated and reported our results, and made up a table that indicated the number of us who could see the Horsehead in some of the instruments we used: generally we'd get a success rate of 4 out of 4, and only once did we have only 1 observer who could see it, while the other 3 failed (when my friend Ryan Wood, then 14 years of age, was able to detect it in his father's 70 mm Celestron Photostar fluorite astrograph. Apparently his youthful eyes were more acute than those of observers in their mid to late forties!)
My research paper has been on the Net since October 2005 -- as the third part of our Horsehead Project website series of articles -- and has acquired about 5,600 hits in that period of time, though I have no idea how many readers have absorbed the contents of the table showing our results. I do know, however, that hardly anyone has ever mentioned it in a newsgroup or forum post (with one exception that I know of for certain.)
This was a semi-controlled test series, involving four people whose ages ranged over 3 decades, including a youthful novice and some highly experienced viewers. The results indicated that, indeed, the Horsehead could be seen fairly reliably in high quality telescopes of 8 or even 7 inches' aperture, and in 11x80 binoculars (plus all kinds of instruments in between, including a cheap near-toy grade "Astroscan" 4 inch scope.) Nebular filters were usually necessary, but not always. And, the observing site was about a 12 mile shot, as the crow flies, away from the heart of San Jose, California and the Santa Clara valley, where hundreds of thousands of souls live and work in a modern, over-lighted, metropolis.
This was not, then, a test done under ideal conditions; nor one that was restricted to the anecdotal experiences of ONE observer. I'd consider it fair to generalize that given clear enough air, and some consideration of proper technique, the Horsehead is by no means an impossible object for an 8 inch telescope, nor one that is much smaller.
Yet, if you look at some of the things posted, even today, it would sound to the beginner as if the Horsehead was the badge of honor of an expert who had invested a lifetime of experience and a pot of money toward the quest.
I recently summarized other reports that I found, contradicting this elitist point of view, in a commentary added to the "Update" section of my Horsehead Project website. Read it, scoffers, and click on the hyperlinks. Report after report, from well known and UNknown amateur astronomers, confirm the results of our 1989/90 tests.
Now, with this background I present some comments that came to mind when a friend and I looked at some recent Horsehead "advice". In addition, I offer a summary of my Horsehead observations done in the last two years, plus drawings I made in 1989.
I am not quoting exactly the very words of the forum thread to which I objected. That particular discussion doesn't matter specifically; the ideas expressed are common mistakes. I've paraphrased them to get away from putting any onus on one individual with whom I might disagree. And, of course: I'm just an individual person, like anybody else; I don't assert that I am always 'universally right' and that others are 'objectively wrong' in everything said here; some of these concepts are matters of opinion and personal experience. However, where I most strongly disagree is always in relation to facts.
Furthermore: from a logical standpoint, if you haven't been able to see the Horsehead, whose advice is most useful: the suggestions of someone who has figured out the way to seen it with telescopes of 8 inches and smaller aperture, or the opinions of someone who hasn't been able to accomplish that? I do not mean to emphasize myself here; there are plenty of other observers of the Horsehead who have successfully used small instruments in conditions ranging from very good to suboptimal: the proof is in their own reports, with links supplied in this article.
Typical Horsehead Queries and Responses:
• I have only an 8" reflector telescope, and I know that I may be pushing it to try to see the Horsehead with this instrument. Is there any "magic eyepiece" that will enable me to do it? I own a [..........] and a [..........]; should I get a [..........]?
"I tried for more than a decade with my 8" scope -- a standard older model SCT -- and failed. Yet, I use a very dark sky site at a high altitude."
• But...isn't is POSSIBLE with an 8"?
"Well, if you can do it at all, you'll HAVE to:
...use a hydrogen-beta filter in order to be able to see IC-434 at all;
...get that very bright star near the Horsehead out of the field; that's important, while the eyepiece you use is not particularly relevant;
...once you've got IC 434 in view, that H-beta filter is the only way you can see that the Horsehead is a dark spot in the nebula;
...and remember that it is VERY, very very very very hard to see it, even if you are using a ten inch aperture scope, so you can imagine how much harder it is in an 8 inch!
...furthermore, your sky must be incredibly dark (I recommend 6.7 magnitude -- or darker! -- or you don't have a chance.) And, B-33 has to be at the meridian."
• OK; I get the point that my 8" won't be adequate; and I'm not at a "very dark high altitude site" like you are. And, I'm told that the thing is really, really tiny and hard to see, even in a big telescope, right?
"No, it's not tiny at all! It's in fact much larger than you think -- it's about ten arcminutes in diameter: not tiny. It will show at the lowest power because it is so large; but your scope should have (say) much more than 90% transmission of light. It won't be seen in a scope with standard coatings."
• Thanks. That lets out my scope, too. It's hopeless then. If I get such a scope, what kind of eyepiece do you recommend?
Another, different guy chimes in now.
"Well, if you spend $1400 on an image intensifier eyepiece, you can see it for sure."
• Gack. Err, any other suggestions?
"Try an orthoscopic type in the Zeiss brand. And, your best bet is to get the 12-13 inch size telescope, such as mine: I can see it all the time with such an instrument, though it was impossible in my 8 inch. And remember: I'm using a very dark sky site at a high altitude, so it's going to be tough otherwise."
[An aside: the writer of the most explicit and specific advice that I've drawn from the original discussion lives in the southern California region, closer to Hollywood than to San Diego. My assumption is that Mt. Wilson -- usually obscenely light-polluted -- is probably not what he uses. My guess is that it's more likely to be Mt. Pinos; and from my personal experiences at that site at night I would not class the spot where we did our 1989/90 Horsehead tests as at all inferior, in any way. Nor would I personally call Mt. Pinos generally a truly world class dark sky site; that it's still useful at all is due to the altitude. I quote from the 'official' astronomers' website of Mt. Pinos: "Its high altitude, 8300 ft. (2500 meters), puts the site above most of the worst clouds and pollution making for a naked-eye limit (for me at least) of about 6.0 depending on the humidity and other factors, but the transparency has noticeably degraded over the past few years due to new housing developments just to the southeast." -- click here for more information; spelling corrections added here on this present page copy by me, srw. I might add that it is rare that at my site, in the Santa Cruz mountains south of San Jose, the NELM is very frequently 6.0 or far better, so despite the proximity to Santa Cruz, San Jose, Gilroy, and Morgan Hill streetlights, it's a darker sky site than Mt. Pinos. -- srw]
• Oh, my: a friend has one of those Zeiss orthos, but I don't think I can borrow it. I guess the circumstances are all against me: I don't have the right scope, eyepiece, or site; and I misjudged what the thing will look like. Well: thanks for the reality check.
I believe I've done a fair -- though rephrased -- digest of the discussion, which has aspects of many others that I've read on usenet and in astronomy group forums. Is this really the best and most practical advice one can give a less-experienced observer?
A friend of mine who has seen the Horsehead with an 8 inch "stock" run of the mill telescope, without fancy high reflectance overcoatings, read the discussion at my suggestion. He was even more derisive than I had been.
What's wrong with the stuff in the above replies -- my very close paraphrases of what was actually posted -- in the view of myself and a close colleague?
1. The Horsehead's angular diameter is ALL WRONG.
Edward Barnard himself said, in his article in the Astrophysical Journal for January, 1919 (containing a list of 182 dark objects in the sky) that the dark object he identified as B-33 (now known as the Horsehead nebula) was "4 minutes" in diameter. (You may look it up yourself by typing in "33" into the box for "Dark Object listing" on this website that supplies an elaborate search function for Barnard's Atlas of the Milky Way.)
I checked some modern sources. The Saguaro Astronomy Club database (version 7.7) says "6 minutes"; in my opinion, this is on the large side as it represents what may be measured from a photographic plate. The Deep Sky Browser page for Barnard 33, via the website Messier45.com of Mikkel Steine, says 6' x 5', which -- again -- seems large, compared to a good eye-view. Interestingly, the alternative modern catalogue designation for the Horsehead is LDN 1630; but the Deep Sky Browser page for that says 3' diameter!
The astro-atlas TheSky VI gives a value of 6 x 4 arcminutes, based on the SAC database; but when you use the cursor to measure the diameter of the object as it's plotted on screen, you come up with a figure of about 2 minutes.
The late Walter Scott Houston, columnist for decades for Sky & Telescope, states "The Horsehead is only 5' across" in this article. The Robert Gendler picture illustrating the Horsehead, though, is in brilliant color with very high contrast, and the "torso" of the Horse is dead black against vivid rosy red, and extends westward about four to five times longer than its width in the N/S direction.
John Sanford, author of "Observing the Constellations", apparently agrees. I used his figure of 1 x 5 arcminutes for the database of nebulae in my program "Eyepiece", by his permission. However, whenever I looked at the nebula, I tended to perceive reliably that the narrow "head" was about 1 minute, with diverse scopes, while I had varying results in determing the longer diameter: from 5 minutes on down, depending on the contrast of the view.
So the specific "diameter" of this irregularly-shaped dark cloud depends on how you view it! In the dim gray eyepiece apparition, depending on the aperture and filtration, you may only be able to see the "head" (which measures only slightly greater than 1 minute in diameter) unless you have a gigantic scope: for example, something approaching 20 inches or larger. Then, you can can get an absolutely crisp, clear view of the "chess piece" shape, and a fair amount of the long 'torso'.
I have not measured it with a micrometer eyepiece -- and even if I did, the result would be highly context-dependent -- but I'd say that in an 8 inch scope, you might perceive a 30" to 1' dark bump, best case (it would be therefore about 1/10th to 1/15th the apparent diameter of the great globular cluster M-13.) NO WAY would it be likely that you'd perceive the Horsehead as a 10' diameter object -- the size of globular cluster M-107 or galaxy M-65, according to the figures given in this compilation -- as asserted in the misinformed reply above.
By the time Barmard had published his paper and list of dark objects, he had not only photographed the Horsehead and measured the plates, but he also had examined it very closely by eye with the 40 inch Yerkes refractor: in fact, so well that he could distinguish its character as a darkened cloud over a bright nebula, not a "notch" or vacancy (this article of ours has the documentation.) I'd say that the Old Master himself is about right, when he gives a general figure of '4 minutes' for the thing.
So, it is likely in a large scope to be perceived as being about 4' on the longer diameter, but smaller in less efficient scopes.
This is indeed -- to use a relative term -- a "tiny" object. The highly experienced observer and author Steve Coe, in fact, disagrees with "Scotty" Houston, as seen here on the SAC website page for objects in Orion: "I have seen the Horsehead in the 17.5 inch scope at 125X. With averted vision some light and dark detail could be seen, but it was tough. The Horsehead outline is small, maybe the size of the Ring Nebula."
The diameter of the Ring Nebula (M-57) is 86" x 62" according to the figure given by Dr. Harold G. Corwin for the object (as NGC 6720) on the NGC/IC Project website. Ergo, Coe sees the Horsehead in his 17.5 inch scope as being a spot similar in size to the Ring nebula, a bit over 1' in diameter. Remember: that's in a 17.5 inch scope!
As you can see, there is no absolutely convincing concurrence of opinion; but the figure that it is "ten arcminutes" in diameter, given as advice in the discussion thread, is laughably wrong: by some accounts, an order of magnitude too large! Some advice...
2. The telescope advice is ALL WRONG.
We've already discussed the results of my test with four observers, involving a limited application of controls, and the table of results I've published. And I have provided above a link to an article written recently that quotes, and links, other observers using very small optics. These two discussions alone blow away the assertions that an 8 inch scope with "standard" reflecting coatings 'won't work'.
3. The eyepiece advice is ALL WRONG.
The advice given (my paraphrase of the original statement, which is almost identical in wording) that "...the eyepiece you use is not particularly relevant..." is so simplistic as to mislead the uninitiated experimenter. There are indeed important issues both of quality, and of performance in a given telescope, that can cause dimming of the image or reducing contrast to the point that the very slight difference of brightness -- at some wavelengths of light -- between the Horsehead cloud, and the background on the eastern and western sides of the dark nebula, won't be detectable.
Beyond the Horsehead 'trunk' to the east (toward the "7 o'clock" corner in this picture) is a larger mass -- not quite as opaque -- that partially obstructs the light of dim stars in the region; then there is a sharp bright rim of IC-434, against which the 'head' of the Horse stands out -- at least in a deep exposure photo or CCD image. In a color rendering, the glow of IC-434 is deep red from the radiation of hydrogen alpha wavelengths; but the dark adapted eye is sensitive only to the much fainter greenish hydrogen beta light. In some circumstances, that light is so dim, that a poor contrast view will fail to show the presence of the Horsehead's 'trunk', which is only the slightest bit brighter than the background: it might even be totally invisible in a washed out view caused by stray light scatter. On the western side of IC-434, the 'head' of B-33 just peeks out, a very dark mass superimposed over the 'rim'. But if the field glow from local light pollution is brighter than that, you can't tell that the head is there. The key to being able to see the Horsehead, then, is to (a) know where it is, and how large it will appear; and (b) to get a high contrast view that isn't diminished by scattered, unrelated glow. The eyepiece is ultimately the mechanism by which the light gathered by the instrument is conveyed to the eye.
You will require a high contrast ocular, with efficient light transmission and low scatter. But, above a certain threshold -- which will depend on the brightness of the image, affected by the exit pupil and telescope aperture -- most anything will do. I would suppose that with a 25" telescope, in a superbly dark and transparent sky, an old uncoated Kellner might show the Horsehead. That same eyepiece, in a 4" refractor used at my site in the mountains south of San Jose, would fail to show the object. But another eyepiece of modern, efficient design could do so.
There is absolutely no reason to insist on buying an esoteric Abbé ortho eyepiece, or an image intensifier that costs more than most telescopes. I will illustrate this from my various reports below, using scopes ranging from 11 to 2 inches of aperture, with standard eyepieces that I happen to own: not expensive premium ones nor esoteric designs (mine cost from about $50 to $125: the brand is not absolutely critical, but you should get a pretty good one, as the inferior coatings of cheap ones may prevent getting a decent view with the smallest telescopes.)
Then, of course, there is the issue of the performance of a given eyepiece IN a specific scope, which will vary due to its focal length -- and that of the telescope -- and the eyepiece's apparent field. Wide field oculars with 8 or 9 elements may not always be the best choice: at low power, they might allow the glow of Alnitak and NGC-2023 to 'compete' with the faint Horsehead. Such an eyepiece might have slightly more loss than a fully multicoated 4 or 5 element ocular with narrower field, which will both act to exclude the bright light sources near the Horsehead, and to transmit more photons, since not as much light will be lost at the boundaries of the glass elements. In a very small aperture instrument, you need every percent of transmission you can get. It's not at all predictable for a given situation, except in the most general sense. The only way to see any dark nebula against the faintly glowing background is to get contrast. So, you should test every eyepiece available in your kit, starting with low powers and working up until the view begins to degrade. At some point, for your given situation, you may find an optimal result: don't be discouraged until you have thoroughly experimented.
Users of compound telescopes or refractors may typically employ a star diagonal: these accessories can have light loss and scatter that will reduce the contrast and thus the perception of the Horsehead: so experiment here by taking out the diagnonal (if possible), or by trying a better one if yours isn't highly efficient.
While the Horsehead is by no means the most difficult dark nebula to see visually, it's not as easy as -- say -- B-92 in Sagittarius, shown here. This dim cloud looks like a veritable black inky pool of nothingness, suddenly emerging from a bright and starry realm in the Milky Way, even in my 4.7 inch telescope with no filter whatsoever. You may even examine it at high power, when it continues to be an almost total void, with one or two faint stars inside an empty chasm: an eery sight.
Furthermore, the longer axis of B-92 is at least twice as large as the Horsehead, increasing the contrast effect. The congested star field around B-92 makes the dark mass's presence all the more obvious. This is not the situation with the Horsehead, which has only a few faint stars immediately nearby within about 5-6 arcminutes' radius, which don't have the same effect as the densely populated Milky Way stars right at the edge of B-92. Therefore, since we must judge only slight differences of shading, the higher the transmission of the eyepiece, and lower the light scatter, the better the contrast will be: and the easier it is to see B-33.
4. The filter and site advice is SOMEWHAT OVERSTATED.
As I show below, the Horsehead can be detected with a "UHC type" general narrowband nebular filter (I happen to have done it with my UltraBlock in a variety of scopes, including a c.1979 model C-8 at a county park in California -- not at all a high altitude site: its elevation is only 1400 feet); and I've seen it also without a filter. Jay Freeman reports viewing it with his LPR filter and a 6" Maksutov scope, at a 2500 foot elevation not far from the city lights of Monterey, California: a place that is certainly neither a towering mountain peak nor a critically dark site. This, and other reports -- including Jeff Medkeff's very first view of the Horsehead with a 4.5 inch telescope and NO filter -- are discussed in this article, with links to the originals on the web. But, I agree with the general advice that most people will benefit from the hydrogen-beta filter; I certainly do!
My correspondent friend has observed the Horsehead from Scandinavia with an 8 inch "low end" Dobsonian (an old Orion-US brand), with standard 88% reflectivity aluminized primary and secondary mirrors, and with medium-low-end eyepieces, near sea level at a latitude of about 60 degrees N, and writes regarding the 'advice' given on the forum, "And anyway, it isn't about the altitude of the site and not the meridian... if it would be how could I be able to see it with my 8" here to begin with?" (He observes near sea level, and the Horsehead is lower in his sky than it is in mine in California.)
He sums up: "There is no reason to discourage people like that. And you don't absolutely need the H-Beta filter. 'The eyepiece used is irrelevant?' I think not son! It is worthless posting there: nobody believes you anyway."
Some of My Observations
I have rather exhaustively treated our four-person visual tests in this article; and at the end I added some recent attempts, starting in 2005, to try to confirm the results just by myself, with the newer scopes that I now own. These are so very much "buried" in the voluminous material on my Horsehead Project site that I fear relatively few people have had an opportunity to read them. And, I've done some recent work again with very small apertures, reported in my Google astro-blog of "Faint Fuzzies Observations" -- again, perhaps a bit buried in unrelated contexts. So, here is a summary of my work during the past two winters, preceded by a new view of my old drawings (given originally in inverted mode views in my 1990 Horsehead article.)
17.5 Inch Reflector Telescope
This picture was produced by me, using as a basis Ron Wood's photograph, originally as an "eye view" simulation for my software program EYEPIECE. I made a drawing while observing with my 17.5" aperture f/4.5 Dobsonian telescope (a cheap Coulter, with regular aluminum coatings) at my site in the Santa Cruz mountains near San Jose, in 1989, using a Lumicon H-Beta filter and an eyepiece with a focal length of 18 mm, producing 111x at an exit pupil of 4 mm. Then I used Ron's photo and cropped and processed it in the DOS program "Neopaint" to resemble the image scale and density perceived in my sketch. In 2005 I took that image file and transformed it again into a telescope eyepiece-framed image and show it in positive mode in my Horsehead article: you may see it that way by clicking here, though it's best seen against a dark background. For the purposes of this present article, I've just converted it back to a negative view, as it would appear if sketched on white paper with pencil. This represents one of my all-time optimal views with a large scope (though I've achieved virtually the equal of it with smaller ones, as you'll read below.)
7 Inch f/9 Apo Refractor Telescope
The sketch at left was done by me in 1989 when viewing the Horsehead nebula at the same site, using Rich Page's marvelous 7" aperture Astro-Physics Star-Fire f/9 apochromatic refractor. I wrote in my article, "a 20mm Televue Nagler eyepiece and Lumicon h-Beta filter work together, at 80x, to provide a gorgeous wide field, with no trace of light-scatter from Alnitak: nebulae NGC-2023, IC-434, and B-33 were splendidly defined, the Horsehead being a distinct, very dark, patch that was noticeably dimmer than the general background field sky glow." The positive version of this picture may be seen here.
8x42 Binoculars with H-Beta Filters
My most controversial observation, which I only recently found corroborated by other amateurs, was done by means of a Carton "Adlerblick" 8x42 high quality binocular, with Lumicon H-Beta filters inserted into each eye cup (they fit quite nicely, as a matter of fact!) I had to dark adapt my eyes for an hour, and had prepared by looking at the 1888 photograph taken by William Pickering using the wide-field Bache 8" telescope at Harvard, which showed the entire belt of Orion and the Horsehead as a very small dark patch. So I had a 'feeling' for how small the nebula would be, and where it could be spotted in the streamer of IC-434: and I got it! If this sounds unlikely, then please refer to my recent report of other amateur sightings, including the work of Phil Harrington and John Class using small aperture binoculars. The negative version of this sketch may be found here.
Some Recent Sightings, 2005-2013
I am reviewing and retesting our 1989 Horsehead observations at exactly the same physical location -- within a few feet! -- used fifteen years previously. Here are some recent sightings (excerpted from earlier reports in articles on our websites and blog, though in a few instances I have improved the wording or added more information):
Monday, 5 December 2005: 11 inch aperture scope
Better winter weather conditions than usual in the Santa Clara valley region vouchsafed more stable skies than in previous November and December days, though fog below did not significantly reduce light pollution. Seeing was exceptionally steady approaching midnight, when the constellation of Orion was just about at the meridian. We used my 11-inch aperture Celestron NexStar GPS "goto" scope (with deluxe enhanced coatings) on a motor-driven alt-azimuth mount, enabling us to "park" on the Horsehead region and not to bother constantly readjusting the scope position.
The test star mentioned in our article -- 52 Orionis -- was only barely visible, and not by direct vision but with a slightly averted glance: not propitious. The dusting of Milky Way was only vaguely perceptible through the sky region just to the east of the constellation of Orion. But the transparency of the sky was vastly better than last Friday, Dec. 2nd: with a 40mm Celestron E-Lux Plössl and Lumicon H-beta filter, having very close to the same exit pupil, field of view, and magnifying power used Friday -- but with a different scope -- now the Horsehead was quite distinct, and viewable without ambiguity with direct vision! It was a clearly defined black patch of about the expected shape. The faint 12-13th magnitude field stars around the object were seen even with the H-beta filter. Furthermore, the glow of IC-434 was distinctly different on either "side" of the Horsehead, brighter where expected as shown in photos.
This was, even without light pollution reducing lower ground fog, one of the very finest views of the Horsehead we have ever enjoyed, and a distinct thrill after our previous half-dozen attempts and their disappointing results: the object had been seen, but not as impressively as tonight.
Two reasons will explain the quality of the observation: first, the sky transparency was outstanding; pale emission and reflection nebulae were easily spotted all around the region; M-78 was fabulous, a view to "knock your socks off" even without a filter! Second: the Horsehead was right at the meridian, with a minimum of distorting air to diminish the faint contrast differences...
Friday, 2 December 2005: 10 inch aperture scope
An unexpected clearing, after days of rainy weather, sent us scrambling up to the top of the Santa Cruz mountain range to do some rare winter observing. The air had been cleared of particulates but fog was a problem at the top of the mountain, at 3400 feet above sea level. A huge cloud bank was moving westward toward the observing site, but we had time to try for the Horsehead around 10:30pm, with the constellation of Orion not yet at the meridian.
The scope used was our 10" aperture Orion SkyQuest Dobsonian model with standard 88% reflection coatings. With a 17mm Orion "Highlight" Plössl ocular and Lumicon H-beta filter, the Horsehead was a patch of very slightly darker shading in the faintly- luminous field: we frankly spotted it only because of long familiarity with this object in the FOV. A novice observer might miss this pale dimness-variability. With other filters, or none at all, the region had some very vague and uneven nebulosity above the "luminous ground", but IC-434 did not have a distinct glow. Just as we began to test different oculars, the view "closed down": we were suddenly in the clouds, and our observing session was terminated. But only minutes before, we did see the Horsehead. [However, in the next observation with the same telescope, the Horsehead was splendid: read on.]
Sunday, 1 October 2006: 10 inch aperture scope
Ah, the first good views of Orion for the season! I could not fail to notice the fine faint trace of northern Milky Way stars coursing over the zenith and into the region of the "hunter" asterism. This is not often seen at the site I use, due to light pollution. But low level valley fog had cut off the lights as if a giant switch had been thrown. Quickly I began to scan the constellation for favorite faint objects. The great swath of nebulosity, "Barnard's Loop", was dimly seen in my 10x50 binoculars (as recounted by me in this article); I could also discern a very faint presence of IC-2118, the "Witch's Head" reflection nebula, 2.5 degrees west of Rigel. The "Flame Nebula", NGC-2024 (sometimes called "Tank Tracks") was very distinct in the binoculars, if I took care to get blinding Alnitak out of the field.
These views augured well for the Horsehead; so I turned my 10" f/4.7 Orion "SkyQuest" Dobsonian telescope onto the precise spot -- I know it so well by now that I almost feel I could find it with my eyes closed! I happened to have a 21 mm Orion "Stratus" eyepiece in the focuser, with an Orion "UltraBlock" hydrogen-line nebular filter, used a few minutes earlier to view NGC-2174. YES: the Horsehead was very readily detected. After changing to the Lumicon H-Beta filter, the Horsehead's darkness stood out as a distinctly blacker region, an inky patch in the sky background along the faintly glowing "rim" of IC-434.
I wondered how much magnification the object could bear, being concerned that the filter tends to require a large exit pupil. With lower power, there was too much light from NGC-2022, and streaks of light from Alnitak. So I went to higher power, selecting a very efficient Orion "Highlight" 17 mm Plössl and screwing on the filter. This ocular, in my 10" Dobsonian, provides a nearly a three-quarter degree field, at 70x: absolutely perfect for the proper rendering of the Horsehead so that its outline and shape could be discerned. In fact, I was able to see the elusive nebula with direct vision: as distinctly as in a decent black-and-white photograph. This was surely one of the finest views I have ever experienced, rivalling the clarity I perceived in Rich Page's 7" StarFire refractor 15 years before. It was just as good as the earlier sighting with my C-11: perhaps, in fact, slightly better (as the sky condition was superior.)
The final test: would the dark cloud be visible without the filter? And the answer: indeed it was! B-33's distinct shape was gone; it was no longer inky black: but the small irregular region was barely darker than the skyglow, or the faint glowing breath of IC-434. This surely proves that the Horsehead was indeed visible to dedicated observers in the early days before modern filters. That supremely rare experience of mine was truly a glorious culmination to a fine early morning survey. Not long afterward I looked away from the ocular and noticed that the sky was suddenly very bright to the east of the constellation: not the onset of twilight, but the glow of the zodiacal light (rarely seen this close to San Jose.)
Wednesday, 12 September 2007: 120 mm (4.7 inch) aperture scope
During a test of the performance of my new Orion 120 mm f/5 achromat refractor on
the night and morning of Tuesday-Wednesday, September 11-12, 2007, just after the winds had started to clear the intense smoke of the forest fires that had polluted the air of the Santa Clara valley, I tried out the scope on some difficult, faint diffuse nebulae, such as Sharpless 2-101, shown below This is a nebula that I have seen often at my site, as well as at darker sites down the Pacific coast, in scopes as small as 4 inches' aperture. I recorded in my logbook that on this occasion it was "Beautifully seen - 21 mm Stratus plus UltraBlock [29x, 4.2 mm exit pupil]: glow around 2 fairly br *s, less visible in 15 mm + UB [40x]."
On this same night I also viewed a some Sharpless and Van den Bergh nebulae in and around the huge cluster and nebular complex IC-1396: "Sh 2-129: can trace entire thing around a bright * in central region"; and "VdB 140: barely seen, AV. Not as good without the UBlock."
The other Sharpless nebulae viewed on this occasion were Sh 2-112 and Sh 2-115, both in Cygnus; Sh 2-155, the "Cave" nebula in Cepheus -- described by me on this occasion as "an odd-shaped glow around a grouping of *s" -- and Sh 2-157 in Cassiopeia (about which I enthused, "Spectacular! V br. Effect improved by all the f *s in chains along the brighter lanes of the nebula.")
I looked at a number of Barnard dark nebulae that I'd never bothered to track down, including B160, B161, B162, B163, and B367: all in and around the IC 1396 complex. Most were vague, and required the UltraBlock filter plus discernment with averted vision; but they were distinctly darker than the immediate regions.
One of the ultimate tests of a small instrument is the Horsehead nebula. Yes, it was perceptible in the 120 mm scope; this was my second try, slightly more successful at 3:58 am on September 12 than it had been on September 11, 2007, when I first attempted to see it with this scope. The constellation of Orion was reasonably high though it would be seen much better at the meridian in December or January; thus, viewing the Horsehead in September is not an inconsequential feat. I used several oculars, finding it essential to get Zeta Orionis and the "lump star" NGC-2023 out of the field in order to preserve contrast. As such, with the 25 mm Ultrascopic [24x], the Horsehead was well over to the edge of the field: but still visible, using the hydrogen-beta filter; I also saw it with the 21 mm Stratus eyepiece [29x]. But, please note that the sky was now VERY dark, fog having crept all around the base of my mountain site, cutting off almost every trace of artificial light; and the viewing transparency was exceptional. You won't do this under mediocre conditions!
Saturday, 24 December 2005: 113 mm (4.5) inch aperture scope
I was successful in viewing the Horsehead with a small scope (4" aperture) under terrible weather conditions, confirming the views reported at the same locale in 1989/90 with a similar instrument. Christmas eve 2005 was not graced with clear, cloud-free skies: for days it had been overcast and intermittently rainy. But it occurred to me that this might be an opportunity to find a few clear patches of sky to test a small telescope. I wasn't disappointed!
The instrument was an Orion "StarBlast" Newtonian reflector on a 'table-top' alt-azimuth mount, pictured
during some earlier experiments I made to try to image the moon. I had purchased it so that my wife Regina wouldn't be bored while I was setting up my larger telescopes. It turned out to be a marvelously useful little workhorse, with excellent optics and surprising light-gathering power, vastly superior in every way to the "Astroscan" we had used in 1989 during the original Horsehead observing tests.
I had to wait more than two hours for the Orion constellation region to clear, and to get near the meridian: I sat bored and shivering for nearly 45 minutes in a deep cloud bank that came suddenly over the top of my mountain location. But a mere ten minutes after the drenching fog cleared, after 11pm, I had the Horsehead! I could barely see with naked eye the faint peppering of Milky Way stars coursing through Orion, and saw not even a trace of 52 Orionis, with or without averted vision. Yet my very first try with the StarBlast (plus, of course, the Lumicon hydrogen-beta ocular filter) yielded a lovely view of the entire nebula IC-434, quite distinctly -- but dimly -- glowing, and extended almost all the way out to Sigma Orionis, as in a photograph. Despite having Sigma, Alnitak, and NGC-2023 in the very wide 2.9 degree field of view provided by an Orion Ultrascopic 25mm ocular (yielding a 6.3 mm exit pupil and 18x magnification) I could very clearly see the dark edge of IC-434 where the nebula is blocked along our line of sight by light-absorbing matter. And, at the correct location (between the approximate focus of three stars in an arc on the Alnitak side, and a parallelogram of four stars on the opposite), that darkish boundary edge had a smallish, darker smudge: the Horsehead!
But unlike the view with my Celestron C-11 described above, the Horsehead's shape was not easy to perceive. With neither direct nor averted vision could I tell precisely where the darkest part was positioned, nor how far it extended (as it blended so subtly from the slightly less dark region surrounding.) It seemed merely a slight difference in the dim extension. I would expect this kind of view of the Horsehead to be acknowledged only by an experienced observer who has seen it telescopically many times. But IT WAS THERE, unmistakably: for when I switched oculars to a slightly higher power, it became even more apparent, with a more noticeable contrast of darkness.
Using an 20 mm Orion "Expanse" eyepiece I got my optimal view (with a 5 mm exit pupil, magnification of 22.5x, and FOV of 2.9d.) The object became more elusive at an even greater power, with an Orion "Highlight" Ploessl of 17 mm focal length (26.5x, 4.3 mm exit pupil, 2d FOV.) I also tried moving the telescope so that Alnitak was out of the field; this helped but was difficult with the oculars that gave nearly a 3 degree field!
Without the hydrogen-beta filter I could not even see the dark boundary to IC-434, nor really any trace of the nebula's faint gray glow. It only reappeared, dimly, with the addition of a narrowband filter (Orion "Ultrablock"), though the Horsehead was still utterly invisible.
Eyepiece efficiency and light transmission may be important with small telescopes. For example: the 25 mm "Sirius" Ploessl that came as an accessory with another of my Orion telescopes failed to show the Horsehead, even with the h-beta filter. Yet the more expensive, higher quality "Ultrascopic" 25 mm ocular, with exactly the same focal length and apparent field, had distinctly higher contrast and sharper focus; the Horsehead could now be detected.
Large exit pupils are essential for the h-beta filter, and they are doubly essential for seeing the object in a very small aperture scope. While the best views are obtained with a narrow field, exempting the bright objects in the region, this is difficult to achieve in a short-focus "richest field" scope like the StarBlast (an f/4 instrument.) But a consequence of the small aperture is that Alnitak, Sigma, and NGC-2023 will not be overpoweringly brilliant. So, as in our tests with binoculars, the Horsehead could still be seen in a wide field, as assisted by the all-important filter.
What is even more remarkable about this sighting is that it was accomplished with the cheapest commercial telescope I've ever used for observing the object up to that date: the StarBlast cost me a mere $169! Of course one had to use the Lumicon filter ($99) and a very good ocular (another $100) but this illustrates that even so-called "beginner" equipment may be very useful, providing it has the outstanding optical quality of the amazing little StarBlast!
I frankly consider this a sort of ultimate test of a small telescope; the StarBlast passed it -- but be aware that beginning Horsehead observers probably won't be as lucky. First: you have to know exactly what to expect from much prior experience at low power. Then, you must use a hydrogen-beta filter that is very costly; and also preferably a very expensive, high transmission, low loss eyepiece, not just any cheap old thing at hand. The Horsehead has to be well situated in the sky, which MUST be transparent and dark. Then, you stand a chance.
Thursday, 23 August 2007: 50, 80, 113 mm (2", 3", 4.5") aperture scopes
In my blog article, "What Can You See with a 2" Finderscope?", I document the work that went into the preparation of some narrowly configured tests of 50, 80, and 113 mm aperture telescopes at the same site as all these other observations discussed in this article. Aware that some skepticism has been expressed by persons who did not believe my observation of the Horsehead with 8x42 binoculars bearing Lumicon filters, I hope that this 'monocular' view with 50 mm's of aperture will help corroborate what I was able to achieve fifteen years earlier. By now, I have viewed the Horsehead around 50 times, at the very least, and many of them were with small scopes and at low power: so I know what to expect.
During the viewing session of the early morning hours of 23 August, 2007 I saw the Horsehead with the 2" lens! The little telescope was made by me from the 50 mm objective from a Celestron finder, using a new tube assembly and high quality star diagonal and eyepiece, as described in the article mentioned.
At 4:40am, I recorded that my the 3" Orion ST-80 scope, "Got it, barely, with 25 mm + H-Beta F at 12.5x"
Five minutes later: "2 scope": same eypc, filter - no. Took off the star diagonal, substituting an extension tube. Since Orion was down pretty low, was able to move my observing chair base so that I could sit and look DIRECTLY into 2" scope. Used 17 mm Pl. and H-Beta: NOT QUITE.
But, with 20mm + H-Beta" YES. Using AV. IC 434 was very br and distinctive. Started to perceive a 'difference' in it, at the right spot...
4:50am. FINALLY got it -- could see HH with 15 mm + H-Beta: looked like a discontinuity in the long stream of IC-434, very black, with my eye off the center of it. Probably would have been downright EASY if Orion had been up high (if I could have put my head down low enough to see thru scope w/out diagonal!) Could see Milky Way clearly thru N edge of Orion coming up almost from the eastern horizon: dark, dark sky!."
I don't think under the circumstances I could have seen it at 8x but only with one eye, though I had seen it years ago with two eyes at that magnification, using the binocular. First, I was of course then considerably younger; and second: binocular vision helps build up contrast and discrimination. I was lucky enough to see it at about 13.3x with one eye; I proved my point about using small optics to discern amazingly faint things.
I think one has to do this kind of experiment, in a very dark sky with carefully controlled conditions, to be able to accept such an "unlikely" claim.
But, I feel strongly that I saw the things I have described here. It would be illogical of me to take the view of knee-jerk skeptics and try to PRETEND that I didn't. Clearly these experiences were stronger and more convincing than self-delusions. The question is: how repeatable are they? Find out for yourself by trying -- repeatedly.
Wednesday, 1 October 2008: C-11 scope
One major difficulty besetting the users of long focal length Schmidt-Cassegrain scopes (often of f/10 focal ratio) is getting an exit pupil big enough for an efficient use of the hydrogen-beta eyepiece filter. It isn't easy to find oculars with focal lengths longer than about 40 mm, even in 2" barrels: so (for instance) with my C-11 scope, I can't get an exit pupil larger than about 4 mm. The Horsehead can be seen, but sometimes not as effectively as when using a 5 mm exit pupil. As of this writing I did not happen to own a 2.0" H-beta filter, and could only get a 4 mm exit pupil in my C-11 with my 40 mm 1.25" Plössl.
So, when I found a 0.5x focal reducer for a very affordable price, on the Owl Astronomy website, I jumped at the opportunity and ordered one. At the time I placed my order (early fall of 2008) the price was only $29.95, and the owner of the company assured me it was fully coated and had very good light transmission through-put. I received it in about three days, and immediately tested it on appropriate eyepieces in several of my scopes. There is a male thread set on the "output" side, which will screw onto an appropriate threaded eyepiece, with a female thread on the "input" side that will allow one to add a nebular filter. Unfortunately it required too much focuser in-travel for some of my very short focal-length refractors and reflectors, but it worked fine on the C-11-- though I did notice vignetting and a significantly reduced field of view. However, that is exactly what you want for viewing the Horsehead nebula: a narrow field, to eliminate the "competing" bright stars!
I had an opportunity to try it on the Horsehead on the morning of 1 October 2008, during a night with steady and transparent sky but not much light- reducing ground fog in the valleys below my mountaintop site: I would estimate that the NELM in the region of Orion was about 5.8 to 5.9 magnitude. Normally this would not give a high-contrast view of the Horsehead, even in the C-11: but it would be detectable with a 40 mm eyepiece at about 70x, with a 4 mm exit pupil. However, now I was able to use my high efficiency Orion "Ultrascopic" 25 mm Plössl. With the 0.5x focal reducer, it provides about 59x at a 5 mm exit pupil, for a slightly brighter image. I noted that the resulting field of view was only about 17 to 18 arcminutes, so that by manuevering the scope a bit I could manage to get as many stars out of the field as possible. The (mirror-image) plot I generated with TheSky VI, below, shows approximately the same total field. Thus, I was able to avoid having the very bright 7.8 magnitude star SAO 132464 / HIP 26816 within the field, the "engine" that excites the reflection nebula NGC-2023. In a telescope of 10 or 11 inches aperture (and larger), the star+nebula are SO bright that they severely detract from the dim Horsehead dark nebula.
I viewed the Horsehead with great pleasure, now being able to see it better than I recalled ever before in the same scope, despite the somewhat below-optimal sky darkness. I wrote:
3:53 am. Horsehead. Not quite visible in 4.5 inch scope tho' perceptible in C-11. Using 40 mm PL [~70x, 4 mm exit pupil, ~39' FOV] + H-beta filter, B33 is better than with 32 mm eypc [87x, 3.2 mm exit pupil]. But 32 gives larger scale, easier to see "head" & shape, w/o focal reducer. Added f.red. and tried again with several eypcs. BEST in 25 mm + f.r. [~59x, 5 mm exit pupil] + H-beta: for first time in C-11, the "neck" stands out further above the dark edge of IC-434: almost a 3D effect. Remarkable -- when I get my eye at exactly the right position for slightly averted vis., with cloth over head to cut off all external light. VG! With f.red. + either 21 mm Stratus [~80x], or 25 mm Ultrascopic, + H-beta filter, could see a 'rim of light' around the head. Shows up on photos but first time I remember seeing so clearly, by eye, in a scope-view. But must not be a 'great HH night' as it does not show up in my 4.5 inch scope with certainty -- and has before numerous times.
The rough sketch, above, is not exactly representative; I only spent a few seconds drawing it. But I did try to show the almost 'shimmery' rim of light around the head of the nebula, and that the 'trunk' was longer than it usually seems: often it just fades out quickly into the dark background. The 5 mm exit pupil really helped!
Note: I have found a very interesting digital image -- by Connecticut amateur astronomer Leo Taylor -- that shows the 'rim of light' around the Horsehead, evoking the view I had with the focal reducer, although of course the scale and contrast are different, with more detail than I could discern by live-eye. Click here for the picture, produced by Leo with a Meade 2080 Schmidt-Cassegrain at f/10, with SBIG ST-7E imager and Astronomik H-alpha filter: four 20 min exposures. This image is found on his "NGC Nebulas Part 1" page, on Leo's website.
Monday, 6 October 2008: 10" scope
During the early morning hours of this late fall session I made some further experiments with the focal reducer, now using it with my 10" f/4.7 Dobsonian. I found that the best combination for the Horsehead was with the 12.5 mm Orion "Lanthanum" eyepiece, which has an intrinsically narrow field of view. I took down notes between 5:05 and 5:28 am that I had a "wonderful view: narrow field, Zeta & N2023 out of sight; extremely high contrast, nebula quite dark. Could see 'head' pointed toward v br star [SAO 132451 / HIP 26756] with shape easily seen...super contrast, & IC-434 v bright! Best combination: 12.5 + f.red. + H-beta filter [48x, 5.2 mm exit pupil, ~10-12' FOV]."
Below: a larger picture of the focal reducer, H-beta filter, and 12.5 mm Lanthanum eyepiece combination, showing how the units screw together. - srw, 10/17/08
Tuesday 13 November 2012: 10" scope
I am now officially "old", being on Social Security and Medicare. Yet, I can still see the Horsehead nebula, though the sharpness of vision in my dominant right observing eye is a bit diminished, with somewhat more astigmatism than, say, five years ago. I continue to use several sky objects as tests of my visual acuity, including the Orion nebula's trapezium (for clarity), dim stars and faint low surface brightness galaxies (for limiting magnitude), and -- especially -- the Horsehead (for contrast range distinction.) I have had two observing sessions just approaching the November 2012 new Moon, at the regular mountaintop site north of Santa Cruz, California, both using my 10-inch aperture Orion f/4.7 Dobsonian, making many tests of not only some recent scope base modifications, but also my own eyesight and perception performance.
On Saturday night 10 November, the weather had just cleared and storm-front conditions were evident in the north bay area though the Monterey Bay south of Santa Cruz was cloud free. I tried the Horsehead nebula around midnight during this weekend, and found that I could only just barely discern it with a 20 mm ocular and H-beta filter, using my 'good' left eye (and couldn't detect it at all in my non-dominant right eye.) Does this indicate old age visual deterioration? Not at all! For, on the next night I tried -- Monday/Tuesday night, 12/13 October -- the weather was MUCH better: after midnight the local temperature was much higher than in the valley below, due to an inversion: hovering just under 60 degrees F, with humidity of about 18% and no winds: nearly like a summer night. Sirius did not even twitch! I looked again for the Horsehead after 2 am, when it was near culmination and -- at 2:15 -- about 50 degrees above the horizon. Same eyepiece and filter. Huge success!
At 60x [4.2 mm exit pupil, just fine for the H-beta filter] the dark nebula was clearly seen straight-on with utter presence: a coal-black body superimposed on a faint sheen of light beyond, with faint stars all around it. I increased the magnification. Using 80x, I could now see the 'shimmery rim of light' described above, and trace out the exact shape of the apparent 'top' of the Horse's head. I then tried 96x (about 4 times the approximately optimal magnification required to see it in a 4-inch class scope, with huge exit pupil), one of the highest magnifications I've ever used on it in a scope of this size class. The Horsehead had virtually the 'chess piece shape' appearance described by amateurs using huge scopes.
THIS PROVES THAT YOU MUST NOT JUST TRY ONCE, GIVE UP, and CONCLUDE YOU CAN'T SEE IT! The Horsehead can be elusive when the meteorological conditions are not absolutely favorable. Some degree of light pollution isn't even an absolutely deal-breaking obstacle, as there was no trace of ground fog or clouds beneath my site and quite a bit of sky glow was evident; I doubt that it was exceeding 6th magnitude naked eye limit at the zenith. Once again: (1) overall humidity should be low; (2) you should try at the highest altitude site you can reach; (3) attempt to view the object near time of culmination and not when it's too low; and (4) experiment with all practical magnifications to see what works best. - srw, 11/13/12
Friday 14 December 2012: 10" scope
"Rules are made to be broken." So many persons have asserted "rules" about what size scope aperture or what naked-eye limiting magnitude are "required" that I almost wonder why anybody tries to see the Horsehead. And, ironically: if you just take a small amount of effort to use a search engine and look for independent observing reports by persons who actually DO see the Horsehead, and get a feeling for the diversity of both instruments used and conditions experienced, you by no means come to the same simplistic conclusions, nor find corroboration for the reality of those "rules". In my own large website about the Horsehead nebula I have given some guidelines, among them that my group of testers in 1989 found that one might need to be able to discern the star 52 Orionis by naked-eye to vouchsafe a pretty good indicator of success with the Horsehead--at least in the telescope sizes we employed (up to 8 inches' aperture.) This star (actually a double, consisting of two nearly equal stars of about 6.1 magnitude, separated minimally at only a bit over one arcsecond) has a total visual magnitude of approximately 5.2; but seeing it straight-on with the naked eye does not mean that you definitely can, or cannot, see also the Horsehead. It's merely one indicator that the sky has enough steadiness and transparency to start to make it possible.
Furthermore: spotting the star, even with averted vision, is helpful. I observed the star, and the Horsehead, twice during this past week: once at a low-altitude (~900 ft) observing site southeast of Soledad, California on Tuesday early AM on 11 December 2012. Although the Milky Way was very strongly discernible just to the east of the major constellation stars of Orion (and the seeing was so steady that I split the double star into two beautifully formed, brilliant pearly globes, almost touching, at 341x), I was surprised that I did have to use slightly averted vision to HOLD it by naked eye. But of course I am 23 years older than I was in 1989; and I now have eyeglasses that use uncoated plastic lenses; the old ones I formerly used during the HH tests were premium-priced ones with anti-reflection coated glass lenses. Plastic eyeglass lenses have a significant light loss, compared to coated glass, as I have carefully discerned in my own personal tests (remember: I do NOT use eyeglasses for observing through my scopes.)
I found B33 to be "just ok" in my 10" Dobsonian, with H-beta filter at 57x. It was not an all-time great observation, and seemed to be merely a dark lump of slightly ovoid shape.
Now: move 85 miles north, to my regular observing site south of San Jose, at 3,400 feet altitude above a sharp drop to sea level, on the mountain range. Today (at 12:06 am) I used the same scope, filter, and eyepiece, and recorded in my logbook the following entry:
HH. Sky seemed so washed out (for instance, NO discernible MWay to E of Orion) that I wondered about the visibility of the HH. No trace of it in the 21 mm Stratus (57x) with no filter. But put in H-β: WOW! The HH jumps out, with good sense of its shape; v dark; not even requiring A/V!! Just goes to show that I'm right about its vis. in skies under 6th mag--as long as other aspects are superb. 52 Orionis is definitely vis naked-eye but only JUST barely perceptible straight-on.
I split 52 Orionis with a 4 mm Vixen NPL eyepiece (298x): and it was definitely accomplished, but the seeing was somewhat rougher than it had been on Tuesday at the other location. There was now a constant jumbling/twitching of the star definition, which hadn't occurred at the lower site earlier!
So, here you have two observations during the same season, within 85 miles of each other, with same observer, same instrument, same accessories. Weather was about the same: clear sky for a day or so, in the midst of generally cloudy and mildly rainy weather, preceding and following. The darker site was much further from city lights, and the one bothersome light dome was about 100 degrees away from the constellation Orion. The Milky Way was resplendent. The steadiness was excellent, with a flawless, elegant textbook close double, 52 Orionis. YET... oddly, I found that star pretty hard to see by naked-eye unless I used averted vision. And, the Horsehead was detectable and identifiable, but a bit vague, without a clear 'shape'. Averted vision helped discern it.
Now, move ahead about 49 hours. Closer to San Jose, with population well over a million and huge light dome all over the general northerly directions. Also a significant light dome from nearby Gilroy, to the south: with direct vision of countless bright city lights at the distant horizon. More than three times the altitude; but the seeing seemed NOT QUITE as good -- unusual for the locale. NO trace by unaided eye of Milky Way near Orion. The naked-eye limiting magnitude was well under 6th due to all the scattered light: the general sky color to the south was a washed out dark blue-gray, not the impressively black sky (festooned by a peppering of countless stars) seen during the previous occasion. Yet the Horsehead was much better: clearly seen straight-on; shape well defined (a 'horse's head' and not merely a featureless ovoid lump that was darker than the surroundings); the glow of IC-434 was much more apparent in the eyepiece (very surprising, considering the washed out sky to the naked eye!); and averted vision was NOT required!
Without any other direct and sophisticated scientific and meteorological evidence to prove my hypothesis one way or the other, I'd assert that the reason that B33 was much more impressive during this week's second observation was that I was now well above the inversion layer, and the sky was simply more transparent. The scattered light pollution glow, visible with no optical aid, was not a factor that ruined the observation in the scope, at appropriate magnification with the narrowband nebular filter. Each of those aids to observing helped compensate for the light pollution!
In both instances, the Horsehead was being sought at the same time of night, at an elevation above the theoretical horizon of about 50 degrees, near culmination. When all aspects of each night's conditions, with and without a scope, as well as with high and moderately low magnification, were compared, there were significant differences (at the lower location, stellar seeing was better; at the higher location, it was more tremulous. Background light was significantly different; faintest stars visible to naked eye varied hugely.)
The interesting (and perplexing) thing is that the night that theoretically should have produced a better observation, due to seeing and background light, DID NOT do so--at least during this particular instance. So, there's more to having success with the Horsehead than just going to a dark sky site!
I also examined Lower's Nebula (Sharpless 2-261, also in the constellation of Orion, at a higher declination) at both sites, finding that I could trace out much of it on Tuesday at the darker site, but had trouble seeing more than one central brightest region at the higher site on Friday morning; yet the Horsehead visibility was opposite, being better at the site closer to San Jose!
Go figure. This interesting comparison reveals that there's not just one simplistic factor that guarantees success, or produces certain failure. The only way to know if you CAN see the Horsehead... is to try to do so, numerous times. If you always fail, no matter what you do: then maybe you can't see it. But, those of use who succeed often also find that the character of the view rather wildly varies, in ways that are surprising (and a little perturbing.) - srw, 12/14/12
Wednesday 16 January 2013: 3.5" scope
I was recently rather shocked -- after having received some very arch criticisms by the well known Nebraskan amateur, David Knisely, who has complained that I shouldn't emphasize the possibility that the Horsehead may indeed by seen in small aperture instruments -- to read in a discussion thread on the Cloudy Nights website that he HAS indeed seen a trace of the Horsehead in his 80 mm aperture refractor:
"...Small aperture reports aside, there needs to be a healthy dose of reality here. To have much of a chance of seeing it (at least for the first time), a somewhat larger aperture is often required. While I have detected the faint band of IC 434 in a filtered 80mm f/5 refractor (H-Beta filter) at 13x, the notch of Barnard 33 itself was not visible with much certainty. At that power, the thing just wasn't quite big enough to overcome the low resolution of averted vision. Once I got the image scale up to where it might have been visible, the magnification diluted the nebula to the point where it was too faint to see much of anything other than maybe a hint of a glow."
David has been more certain with his 4" scope ("Things were a little better in my 100mm f/6 refractor, as at 25x, under great conditions with the H-Beta filter, I could just barely detect the notch (Barnard 33) in that incredibly faint glow, but mainly because I knew exactly where it was to begin with.") On earlier occasions, he has commented directly to me on usenet that "you will probably get a lot of consternation from people who try it with the smaller scopes and fail"; he's also opined that my webpage on the object is "fairly good except for some of the things he says about a few people who just try to cast a little realism on those searching for this ellusive [sic] object for the first time...he kind of falls down a bit by going on a bit too long about it..." I was, he averred, misleading the public because I stated that I was able to see it; my colleagues could see it in the same small instruments in the same observing venue; and many others, whose posted observations with small scopes and even binoculars, could see it, too.
But, I reply: "Who gives the rules for this? What is the cut-off point where you absolutely refuse to MENTION an observation that isn't the kind of view one gets with an 18" Dob in a far-remote, darkest-possible sky?" I can certainly accept that David -- or anybody else -- might say, "Well--I won't mention it and shall ignore those observations"; but is it fair to tell us ALL to ignore them because of a single individual's personal preferences?
Indeed: I believe that it is far more desirable to try to establish a baseline of what has been experienced by a wide number of experimenters. Include the "outliers". Provide all the reports--from small image-stabilized hand held binoculars to gargantuan amateur Dobs and even professional observatory instruments. Don't omit the comments of anybody who has provided enough detail to suggest that the experience was credible.
What some hypothetical "beginner" somewhere will take away from all of this is not relevant to the serious scientific-minded experimenter. But, perhaps it is always wise to add the caveat "you probably will have trouble repeating this observation if you are inexperienced, and your conditions are inferior." There. We've covered ourselves and have NOT 'misled' anybody.
Ergo, I shall provide yet another small telescope report, this time done by me with a brand-new (used) telescope that I had only recently obtained for a mere $100. Now: don't be misled by this. I am not saying "anybody, anywhere, can spend a hundred dollars on equipment and then get an eye-view of the Horsehead." Not so! That used telescope (a) happened to be a very fine instrument, thoroughly tested out before the attempt was made; (b) it was augmented by a very expensive, now rare, discontinued premium Japanese made eyepiece with super high transmission and marvelous clarity; (c) that ocular was equipped with a premium Lumicon H-beta filter (which, as a matter of fact, was hand-selected from Lumicon stock by that company's founder, my personal friend Dr. Jack B. Marling.) And, (d) the altitude was thousands of feet above average terrain, right at the western Pacific coast, in wonderful winter conditions of relatively low humidity, with excellent seeing and transparency...and very low atmospheric water vapor.
These costly accessories were required: a superb, discontinued Japanese made Ultrascopic eyepiece, originally costing over $100; a premium high transmission Lumicon H-Beta filter; and a 0.5x focal reducer, now generally sold for about $50.
Furthermore, the observer -- your present author -- has been studying this object visually since the mid-1980s, having made many dozens of sightings with instruments ranging from high end refractors and giant reflectors, to small binoculars: NOT a beginner.
I have provided a complete chronicle of this event in my Faint Fuzzies Observing blog, in commentary no. 114: "January 2013 Moonless Night Observing", found here. The scope was a 2003 model Orion 90-mm (3.5") aperture Explorer achromat refractor, with an original retail price of only $299. However, it was used on an upgraded and very stable equatorial mount, and the observation was summed up by me as being "difficult, but achievable!" and "HARD: rather frustrating overall" as it required much experimentation to get exactly the right instrumental setup. At last, I saw the dark nebula unmistakably (without a star diagonal, and using a focal reducer to get a 5 mm exit pupil: finding it "trivially easy" to identify ONLY with that exact setup.) Read it all to get the complete context so that you won't be 'misled'. - srw, 1/17/13.
Sunday 3 February 2013: 3.5" scope
Here's a second account of observing the Horsehead with my 90-mm (3.5") aperture f/10 refractor. Same observing site as above (the Santa Cruz mountain range south of San Jose, 3400 ft. elevation); nearly as satisfactory meteorological conditions (temperature 47d F; high pressure, but local humidity higher than earlier; seeing hovering between Pickering 7, worst case, and 8, best case: with some slow rolling fluctuations though stars were sharp looking at high powers. Very clear sky, and with a sharp temperature inversion boundary holding in light pollution from the eastern valley, with dense air near ground level, and much less light glow above it.) "Grainy" Milky Way background evident east of Orion constellation, and star system 52 Orionis visible to naked eye, helped by slightly averted vision. Estimate NELM at zenith: at least 6th magnitude. Horsehead transit time on this night: 8:54 pm.
This was a test of the 2" Eyepiece Adaptor (for 1.25" focuser) that I chronicle in this blog entry. Having thoroughly determined how to use it properly, and any possible percentage of vignetting to be expected (documented here), I wanted to try the Horsehead again, avoiding the 0.5x focal reducer and employing my star diagonal.
9 to 10:02 pm. Horsehead. 42 mm WF (2") eypc does not focus with enhanced 92% star diagonal so have to use standard 88% one. With Hβ filter, HH seen at once (if Zeta Ori out of FOV.) Small, nearly inky black spot. IC-434 v definitely glowing. Only req. slightly averted vis. Seeing now ~8, slow rolling wobbles even up to 40d elev. HH elev. 50d at 9p, per Megastar 5.
Many HH tests over next hr:
56 mm Meade 2" + Hβ, enh. diag: I434 good, HH a bit too small to be more than just a hint of barely perc'd dark speck in I434. 18x too low power, scale too small. Big eypc just too darned heavy for small scope!
42 mm 2", Hβ, prism diag: Maybe I434 a little br'er but contrast seems not as good as std. 88% reflec. diag mirror, so HH v hard: but did get it, A/V, a few times.
32 mm Q-70 2" + Hβ, enh. diag: I434 good, HH almost impossibly hard. Tried UltraBl. filter: NO.
26 mm Q-70 2" + Hβ, enh. diag: way too dark, exit pup too small for filter.
40 mm E-Lux 1.25" + Hβ, enh. diag: No. I434 ok, but contrast not nearly as good as in GSO 42 mm widefield 2" eypc. Have never been impressed with this cheap Celestron E-Lux.
So: best is the 42 mm 2". HH up ~47d when last seen at end of tests. SATISFIED to use 2" eypc's with adaptor (except 56 mm too heavy and tends to slip & rotate.) HH sighting really much easier than earlier test w/o diagonal, using 0.5x f reducer and 25 Ultrascopic--though that combo did seem to give sl br'er view! (No diag.) However, Zeta just has to be out of field!
During this same observing session, about 2.5 hours later, I had an excellent view of the emission/reflection nebula Sh 2-297 (Ced 90 / LBN 1049) in Canis Major, elevated about 31d, and made a good, convincing drawing. After checking about a dozen pages of search engine hits, I cannot find a single amateur visual sighting report online currently (though there are numerous images.) Jaakko Saloranta's CMa page merely states that he has seen it in his 8" Newtonian reflector, but famed amateur Steve Coe does not seem to have published any observations whatsoever. The only commentary with any detail is by Tom Polakis (now offline), who indicates in 15 brief words that he has studied it with a 10" instrument. Since I got it, unmistakably, with a 3.5 inch long focal length refractor, and made a good drawing of a view at 72x, I think this illustrates the excellent efficiency of my equipment and the good conditions experienced at the site.
Horsehead Eyepiece Simulation
The following afternoon, the observations of the Horsehead still fresh in my mind, I created a simulation of how it seemed to be seen in my previous night's view. The 42 mm GSO widefield (65 degree) eyepiece was definitely very efficient: too much so! It was necessary to get the blinding star Zeta Orionis (Alnitak), shining at 1.8 magnitude, out of the field to see the Horsehead as a distinctly black spot. With Alnitak in the field, too much overwhelming brightness caused a loss of distinction and contrast in the dimmer parts of the field. I made up two simulated eyepiece views, the larger one showing approximately the same visual field as the 42 mm 2" ocular in the 90-mm f/10 scope (a true field of about 3 degrees), with an exit pupil of 4.1 mm (very good for the efficient use of the Hβ filter.) One could detect the Horsehead, but quite critical averted vision might be required, with a conscious effort to ignore the glare. It was better to use a narrower field eyepiece (or, at least with the 42 mm, to move Zeta entirely out of the field.)
The second picture shows about half the field diameter, with no direct glare from Alnitak, allowing the eye/brain perception to trace out more glow of IC-434; more distinct faint stars; and a much greater contrast that enables the Horsehead dark cloud to stand out better. Even though it is usually suggested that one place objects in the exact center of the field of view, for best quality, it is often necessary to offset the Horsehead to escape Zeta's light. In a large aperture scope (such as my simulation of the view in my old 17.5" Dob), one may use much higher magnification -- at a large and efficient exit pupil -- and then center the Horshead, avoiding Zeta in the resulting narrower field. - srw, 2/5/13
Find out for yourself if YOU can see the Horsehead. It shouldn't be too difficult to get some small, decent quality optics. Go to a dark sky site (preferably one with HIGH altitude, and dry, steady air.) Test out these and other comparable objects. Try it, and then see what you experience. But: remember that I have been using my observing site for decades, and know the weather patterns and the nights of likely best results. You may not be able to duplicate these views just any place, or any time; but the more often you try, THE BETTER ARE YOUR CHANCES!
As my friend has said, it's perhaps futile to post on forums 'because they won't believe you'; it's also perhaps futile to bring forth this evidence, for SOME skeptics will just deny it on the grounds that it's "anecdotal". So be it. But, if so, then almost every other report of seeing ANYTHING with a telescope is just that.
I've been taken to task for insisting that it has been shown by numerous people that the Horsehead nebula may be seen by persons using small telescopes. The objection given may be summed up as this: "it's hard; you shouldn't mislead people, because they're naive."
My reply is this analogy. Suppose I am a violin teacher, and am writing up a musicological / pedagogical analysis of how to play Paganini's 24th caprice. Do I hold it back, on the grounds that the piece is "difficult", fearing that some novice will try it and go into fits of despairing? Should I fill the whole article with big black boxes "WARNING" that it's a work for an experienced fiddler? No: this may be overstating the situation, and is too discouraging. The world of the intellect doesn't need to be dumbed-down that much. My feeling, having read the context of the objections, is that they generally are always traced back to the critic's admission that the task was hard for that individual. Maybe so. But: does any one person -- and his or her situation -- express all the human and physical possibilities that exist? Of course not. Try the Horsehead; if you fail, at worst you may feel you have wasted some time, though in reality you've learned a lot. At best, you'll see it!
Manager, ROPER PIANO STUDIO
Partner, WALDEE-WOOD ASTRONOMICAL SOFTWARE
Update, 12/08: I have found an interesting post by the expert observer Jay Reynolds Freeman, who has frequently viewed the Horsehead nebula with small- aperture telescopes. In a commentary written back in 1995, Jay perhaps explains one important factor that improves your chances of seeing the faint nebula: ultimate dark adaptation (I have added my own emphases to reinforce certain points):
We looked for the Horsehead Nebula in several instruments. In a 17-inch Dobson at 77x, with a Lumicon UHC filter, IC434 (the background nebula) and B33 (the Horsehead) were well seen; I could hold the Horsehead with direct vision. Without the filter, there was no trace of either. We tried the 155mm Astrophysics refractor with both 44x and 54x, with both a Lumicon H-beta filter and a Lumicon UHC filter. We tried each filter on each eyepiece. The best that some of us could do was suspect B33 at 44x with the UHC filter, though IC434 seemed visible with all four combinations. It was interesting that the UHC filter was doing a better job than the H-beta.
These observations led to an interesting discussion. I have seen the Horsehead in a 6-inch with no filters at 36x on a much darker night; I could even hold it with direct vision. The night of 21-22 October was certainly not so dark, but these filters surely reduced the background glow to as dark as that in any unfiltered observation made this side of low Earth orbit, presumably without diminishing the light from IC434 by any significant amount. Why, then, could we not see the Horsehead in the Astrophysics refractor with filters? One guess had to do with dark adaptation. The brighter sky and occasional lights of camping stuff may have deprived us of that last bit of adaptation that may have been necessary to make a difference. -- Jay Reynolds Freeman -- added 12/18/08
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