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Cosmic Challenge: Horsehead Nebula (Barnard 33)


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Cosmic Challenge: Horsehead Nebula (Barnard 33)

 

January 2022

Phil Harrington

This month's suggested aperture range:

Giant binoculars and 3- to 5-inch (7.6- to 13-cm) telescopes

 

 

 

 

Target

Type

RA

DEC

Const

Mag

Size

Horsehead
Nebula (B33)

Dark
nebula

05h 41.0m

-02° 27.7'

Orion

--

4'

 

Let's kick off the new year with what many consider to be one of the most difficult visual challenges in the sky. If you listen carefully, you might even hear the strains of the "Mission: Impossible" theme song playing in the background. Of all the deep-sky objects in the winter sky, none carries the mystique of the dark nebula Barnard 33, better known as the Horsehead Nebula.

 

Lying 1,375 light-years from Earth, the Horsehead is part of the huge Orion Molecular Cloud Complex, which engulfs much of the constellation. It was discovered in 1888 by Williamina Fleming, not visually, but on a photographic plate taken at the Harvard College Observatory.  Later, Edward Emerson Barnard added it as entry 33 in his burgeoning Barnard Catalogue of Dark Markings in the Sky, describing it as a "dark mass, diameter 4', on nebulous strip extending south from Delta Orionis."

 

The Horsehead is located 1° due south of Orion's easternmost belt star, Alnitak [Delta (δ) Orionis], making it very easy to pinpoint.  But as easy as it is to locate, this "night-mare" is a nightmare to see.

 

Above: Evening star map showing the location of this month's Cosmic Challenge.

 

Credit: Map adapted from 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

 

 

The problem is not the object, but rather our eyes.  The human eye is a marvelous tool with an incredible range.  We can adapt to almost any lighting condition, from very bright to very dark and still find our way around.  But when it comes to dim, red deep-sky objects, it's almost worthless.  That's the problem here. The Horsehead is visible only because it is situated in front of the red emission nebula, IC 434.  And IC 434 is, for all intents and purposes, invisible unless viewed under very dark skies or by using nebula filters, or both.

 

In my book Touring the Universe through Binoculars (1990: John Wiley and Sons), I stated that "the Horsehead Nebulais too small and faint to be visible in binoculars."  I reasoned that it's tough enough to find it through large backyard telescopes, let alone binoculars.  But 31 years ago, at the 1991 Winter Star Party in the Florida Keys, after spending some time observing alongside the late, great Tomm Lorenzin, the talented astronomy author and observer from North Carolina, I found out that I was wrong.  Tomm (short for Theurgically Organic Mankind Module) showed me that the Horsehead is indeed visible in giant binoculars!

 

Here's how we did it.  First, we were in an ideal observing site.  The Keys' crystal-clear skies and Orion's height above the horizon certainly made a big difference.  Next, he taped a pair of hydrogen-beta line filters to the eyepieces of his 10x70 Fujinon binoculars.  Finally, we made sure that Alnitak was just outside the northern edge of the field, while nearby Sigma (σ) Orionis was toward the western edge.  Then, with a detailed chart of the area at our side, we looked for a close-set pair of 8th-and 9th-magnitude stars near the center of the field.  These coincide with the leading edge of IC 434 and are just west of the Horsehead.  With Tomm's help, it took me only a few minutes to pick out both nebulae.  Of course, the Horsehead was very small, looking like a thumb viewed from a few dozen feet away, but it was unmistakably there.  I repeated the observation in my own 11x80 Unitron binoculars after retaping his filters onto my eyepieces. More recently, and under less ideal conditions, I spotted the Horsehead through my 4-inch (10.2-cm) refractor, as captured in the rendering below.

Above: The Horsehead Nebula (Barnard 33) and IC 434 through the author's 4-inch (10.2-cm) f/9.8 refractor.

 

Below: Steve Bellavia (CN member StevenBellavia) took this image of the Horsehead and IC 434 using a Borg 90FL refractor and a ZWO ASI 183MM Pro camera. Be sure to visit his Astrobin page for full information on this as well as his other spectacular images.

 

This is not to say that seeing the Horsehead is a simple task in larger instruments.  Nothing could be farther from the truth.  Indeed, I can rarely see it from my own backyard observatory using my 18-inch (45.7-cm) reflector with a hydrogen-beta filter in place.  So, regardless of the telescope you're using, the Horsehead Nebula is a difficult challenge, one that will test your instrument's quality, the clarity and darkness of your night sky, as well as your skills as an observer.

Before I close, just a postscript about Tomm Lorenzin. Those who have been into observing for any length of time have undoubtedly heard of Tomm's self-published atlas/handbook 1000+: The Amateur Astronomer's Field Guide to Deep Sky. It's still available on the used book marketplace, such as from addall.com and others, as well as on occasion in the CN Classifieds under Software/Books/Magazines/Etc.

 

Tomm also created a sequel, bigger and better than the first that he generously released on his web site for free entitled, appropriately, 2000+: The Advanced Amateur Astronomer's Field Guide to Deep Sky Observing Database & Sky Atlas.  Tomm passed away unexpectedly in 2014, but his family has maintained his online legacy for all to enjoy to this day. If you haven't already, head over there and take a look.

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 challenge.  Contact me through my website 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 2022 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.

 


  • okiestarman56, John O'Hara, Sasa and 3 others like this


29 Comments

Photo
David Knisely
Jan 14 2022 10:18 AM

A UHC style filter is not a great choice for the emission nebula surrounding the HH, because the nebula lacks much in the way of OIII emissions.  This matters because UHC filter bandpass is considerably wider in order to reveal H-beta and OIII lines.  Good samples of UHC have a bandpass about twice as wide as good H-beta filters.  

 

On the other hand, a good H-beta filter is considerably narrower (about twice as narrow), reducing the general glow of any light pollution and natural airglow without damaging the emission signal.   The signal to noise ratio of the H-beta on appropriate nebulae can be about 2x as great.

Actually, the very first time I ever got  to see the Horsehead nebula was in the original 1980 version of the Lumicon UHC filter at one of our Prairie Astronomy Club rural star parties some distance south of Lincoln, Nebraska.  I was using a friend's Cave 10 inch f/5 Newtonian with his "new" UHC filter and could see the dark notch of the Horsehead fairly clearly, although it was pretty dim.  I borrowed his filter and took it to my own 8 inch f/7 Newtonian,where again, I managed to see it, although not quite as well.  In neither instrument was the Horsehead visible without the UHC filter.  Although the H-Beta is a better filter for the Horsehead than the narrowband filters are, the use of a good narrowband like the Lumicon UHC will definitely improve your chances of seeing it.  Clear skies to you.

    • John O'Hara likes this

I had a buddy a long time ago who lived on the Frio River, an hour and a half west of Austin, on the Edwards Plateau I think. Nearly perfect viewing conditions. We used to take a swim late in the evening and then lay on the big granite rocks along the shore. They would get heated up during the day and be nice and warm to lay on most of the night. The night sky out there was just incredibly beautiful. He taught me a little trick. If you laid on the rocks and looked up, let,your eyes adjust for a good half hour and then relax your eyes, so that you aren’t looking at anything, but everything - if that makes sense…. Anyway, after a while, you would start to see satellites- quite a few of them. Just with the Standard Issue Mark I eyeball!  
it took a little practice to be able to relax your eyes like that… this was in the early 90s. The one time I saw the horsehead nebula,  I had to relax my eye like that, as best I could. It’s a lot harder to do looking through a telescope than staring up from the hot rocks. As I mentioned earlier, it was my (now ex) wife who spotted it first, she came up with the ides of relaxing the eye like we did on the hot rocks. I had it dead on and couldn’t see it, until I tried several times to look, but not look, if that makes any sense.

on those hot rocks, when you spotted a satellite, if you tried to focus your eyes on it, almost always, you would lose it.  
 

I completely agree with “Surveyor I” - seeing it is almost a misnomer!

 

Blue Skies & Clear Nights!

 

-Kealey

    • John O'Hara and Knasal like this

Actually, the very first time I ever got  to see the Horsehead nebula was in the original 1980 version of the Lumicon UHC filter at one of our Prairie Astronomy Club rural star parties some distance south of Lincoln, Nebraska.  I was using a friend's Cave 10 inch f/5 Newtonian with his "new" UHC filter and could see the dark notch of the Horsehead fairly clearly, although it was pretty dim.  I borrowed his filter and took it to my own 8 inch f/7 Newtonian,where again, I managed to see it, although not quite as well.  In neither instrument was the Horsehead visible without the UHC filter.  Although the H-Beta is a better filter for the Horsehead than the narrowband filters are, the use of a good narrowband like the Lumicon UHC will definitely improve your chances of seeing it.  Clear skies to you.

UHC would still not be my first choice, hence "not a great choice" in the post of mine you quoted.  It certainly would not have worked when I detected the HH in town with an 8" SCT and H-beta.  Even a good UHC is half as good for the job as an H-beta.  And of course there is the problem of various generic broader band "UHC" filters that have about twice the band width again, so that they are roughly halfway between a narrowband and unfiltered.  The progression is roughly:  H-beta 2x better than UHC (narrowband) which is 2x better than a wideband "UHC/light pollution filter" but even the latter should be about 2x better than unfiltered.

 

What I have not tried is an even narrower H-beta, ones with bandpasses in the low single digits.  Doubling the signal to noise yet again could make a big difference for hydrogen emission clouds in general.  Those filters could be tricky because of wavelength shift at fast ratios, but some folks swear by them.

    • John O'Hara likes this

Beautiful night last night(Sugar Land TX) spent a couple of hours on Orion, but no luck with the horsehead…. Great views of M42 and the flame. Tried a couple of different filters, great on other stuff in/around Orion…  

    • John O'Hara and Knasal like this


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