Thanks to all who have referred to my Horsehead Nebula web articles.
I appreciate the kind words. It isn't always that way; when I finally worked up the courage to inform readers of sci.astro.amateur of the site, which would take someone about 2 hours or more to read, I noticed that within less than TWENTY minutes of my posting its brand new URL, there was a criticism of it, saying (in effect) that all it would do would be to annoy people, by 'claiming' that it could be seen in small instruments.
Well, it's no "claim". It's a fact. The site has an extensive section on observing and photographing it in small optics, including data of four observers who used a variety of telesecopes in the winter of 1989/90, which I am repeating at the same spot to see if increased light pollution "kills" the Horsehead there. As you'll see from my recent reports added at the end of the article, it is STILL quite visible when (a) the sky darkens enough so that stars of about 5.5 magnitude can be held clearly by DIRECT vision; (b) on nights of superb transparency; and (c) when the HH is nearest the meridian, as high as possible. Furthermore, a filter of the H-Beta type is almost always required, and with one, and a 25 mm Orion Ultrascopic Plossl, I used my wife's little $169 Orion StarBlast 4 inch aperture f/4 reflector to see the HH, repeating some of the feats of the 1989/90 tests. On a superb night, I saw the HH with NO filter, which surpassed any of my previous efforts which had always failed: on that occasion, my 3,400 foot altitude site in the mountains south of San Jose (on private property: sorry!) was "closed in" by ground fog below, cutting off virtually all artificial light, resulting in "high desert rural skies" such as I'd experienced in Nevada.
Within the last two winters I have had views of the HH with my 10 inch f/4.7 (cheap) Orion Dob, and my C-11, that rival the best I've ever had, at this site. I seriously doubt, though, that folks who use low altitudes and who can't get away from light pollution are going to have a lot of luck.
Somebody in this thread said that the HH was about the size of many galaxies that one observes, and gave dimensions. But, unfortunately, they were not quite correct: as far as VISUAL observers are concerned, the HH is only about an arcminute (or 2 at most) wide by perhaps 2 to 3 arcminutes long, as seen in most amateur sized scopes. The published dimension of 6x4 is overstated (re: visual) and based on photographic measurements. It seems incredibly small when viewed with low powers (such as the 16x I employed with my Astroscan, or the 18x in my StarBlast, or in 8x or 11x binoculars.) And, "dark against not quite so dark" is harder to discern than a light galaxy against a dark background, in my experience.
Generally the key to being able to see the HH is the exit pupil employed, not so much the sheer aperture of the instrument. Jack Marling's rules for the appropriate exit pupil for his filters hold well for the HH and the H-beta filter, even if they are made by other companies than Lumicon. You may look at the Lumicon site for a chart, on this page:
http://www.lumicon.com/categories_sub.php?cid=1&cn=Filters
Also, I use those values in doing calculations for filters in my old DOS program, which I now give away free:
http://home.earthlink.net/~steve_waldee/index.html
Furthermore, my program actually can calculate the predicted visibility of the objects in its databases, including the HH, based on various optical parameters and the surface brightness and wavelengths of light to which the eye is sensitive.
When I did my test in '89 and discovered that I *could* actually see a sort of miniscule semblance of the HH using 8x42 binos fitted with H-Beta filters, it was an outlandish claim; but others are now doing it too, though not necessarily with such small aperture. However, the 8x42s had an exit pupil that is within range of the right size for the filter, maximizing the contrast enhancement.
Of course, to see it that way, you're going to have to have a lot of prior visual experience with the object so that you'll know what to expect.
Those of you who are going to attempt to view the HH with a refractor, Mak, or SCT: please try it WITHOUT a star diagonal! This will help enormously unless you are using one of the new premium dialectric ones with 99% reflectance. And, I can say with confidence that often refractors give the best results, their higher contrast -- having no central obstruction -- sometimes making the critical difference. Thus, those of us who did the tests back in '89 found that Rich Page's wonderful AstroPhysics StarFire 7" APO gave us views of the object that rivalled a 17 inch Dob (believe it, or not!)
To find the articles about the HH that I have published, go to the main menu of the HH site:
http://home.earthlink.net/~astro-app/horsehead/index.html
There are three fairly readable articles following a general introduction; the third article "Pt. 3 The 20th Century; Viewing the Horsehead in Small Telescope" has, at the end, a long section on viewing techniques, with many images and links. The other articles deal with its UNKNOWN history: its discovery -- by a female member of the Harvard College Observatory staff -- and all the subsequent photographs published in the next several decades, and my not quite successful attempt to track down PRECISELY who gave it the nickname. The last article is a very long, detailed paper with footnotes (sadly, a few of those references have been lost), which I reconstructed from a copy of the paper that turned up last year. All the original material was sent to Kalmbach Publishing - but they put it in storage and LOST it! I do not have any of the original pictures in the pristine prints that I collected, but did my best to process the xerox copies that I saved, so the FIRST HH photo is indeed included!
Steve Waldee