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Geoff Barnes

Pursuing the Horse.

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We've been blessed with some wonderfully clear and transparent skies of late here (Melbourne Oz region). As a result I've been having a look at some of the more indistinct targets with my 12 inch Dob. Inevitably this has resulted in a fair bit of time trying to spot the elusive Horsehead Nebula, Barnard 33, with Orion being particularly high in the sky here during our summer months.

With my Baader 8-24mm zoom and Astronomic UHC filter I thought I might be in with a chance, but no such luck so far despite repeated attempts. I'm wondering just how much difference an H-Beta Filter will make to improve my chances? I know it is the filter that is always recommended for this target, so I may well have to invest in one, even though it will rarely get used here, but people do report being able to see it with the UHC filter.

 

Edited by Geoff Barnes

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Sorry I can't answer your question, but thanks for posting this as I was hoping to see the Horsehead Nebula from my back garden the other night and couldn't see anything. I was thinking it was me being stupid, so it's nice to hear when other people have had difficulty too. Makes me realize it's not just me.

I've ordered and am just waiting for an Explore Scientific CLS Nebula Filter from FLO in the hope that might help with that type of object, but I also now think there was more light pollution than I realized at the time. I'm hoping to be able to post a review on here soon as to what difference the filter makes. Although after hearing that you already used a filter I'm a little worried now!

Bets of luck, and I hope someone else can give a good answer.

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I'd suggest blacking out any stray light entering your eye from your surroundings by covering your head and eyepiece with a dark blanket. I tried ten years ago using a Tak FS128 and H- beta filter from a dark site away from town, but all I could see was the flame nebula indistinctly. A couple of years ago while observing with a Tak FC100DC from my garden, and using the blackout blanket idea, I was successful in not only detecting IC434 but also a small notch of black nebula protruding into bright nebula IC434. I wasn't using any filter! I feel reasonably high magnification may help in your quest for the horse head, as the sky background will be darker making IC434 easier to detect. Once youve found that, you should be able to see the HH with averted vision. (Its tiny!) It may be best to keep Alnitak outside the field of view!

Edited by mikeDnight
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Hunt the HH when conditions are optimal - make sure you are well protected from light sources and light pollution levels are low, and also you need excellent transparency. Allow enough time in darkness to become fully dark adapted. Try to spot it when highest in the sky (around the time it crosses meridian), unless there is light pollution from that particular direction.

UHC will help, H-beta will probably do a bit better, but it's not mandatory. You need a bit smaller exit pupil than for most DSOs - aim at around 1.7-2.0mm, with your scope that would be between 8.5mm and 10mm ep focal length. Luckily you have zoom so you can easily try out different magnifications,

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I would not as stated above, suggest reasonably high magnification to attempt this observation. Rather you need to place emphasis on 1) exit pupil and 2) a narrow field of view. For this observation with my 14" dobsonian, an exit pupil between 3.7 and 4.2mm with either a 20mm (x92) or 25mm (x74), I use TeleVue Plossl's (calculated using my paracorr) works very well. A H-beta filter is necessary, although as I understand a UHC could assist in exceptionally good transparent circumstances. Your 12" dobsonian should be enough aperture, particularly where you are located and the high elevation of Orion. It is useful to observe other faint nebulae structures prior to focusing on this region, do not Observe M42 before hand as this will impact on your dark adapation. Having gained knowledge in and scrutinising the exact location, keeping Alnitak outside the field and applying averted vision will gain you this, the Horse Head appears like a thumb print and is like a velvet dark shape in the nebula -  good luck. 

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All good advice so far. It should be possible with your Dob. John did it with a 12” in the UK where it is much lower. 

Scarp15 hit the nail on the head re exit pupil. 4 to 5mm seems to be popular with the Hb; possibly a bit smaller with the UHC. Hb is better than UHC, but it has been done and let’s face it; the Hb isn’t much cop for the majority of targets. 

The right atmospheric conditions are a must. So out the Flame nebula first. If it isn’t clearly visible, don’t even bother looking for the horsey for the night.

Good Luck.

Paul

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4 hours ago, Geoff Barnes said:

how much difference an H-Beta Filter will make to improve my chances?

IMHO you need to determine how dark your sky actually is.....it needs very dark transparent skies. Under these conditions the HH is visible for sure- I use a 25mm TV plossl in my 10" to see it. Your zoom set on 24mm might allow you to see it with the Hb. Many use simple eyepieces to view this object.

Don't get your hopes up unless your sky is truly dark and transparent.

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3 hours ago, mikeDnight said:

I'd suggest blacking out any stray light entering your eye from your surroundings by covering your head and eyepiece with a dark blanket. I tried ten years ago using a Tak FS128 and H- beta filter from a dark site away from town, but all I could see was the flame nebula indistinctly. A couple of years ago while observing with a Tak FC100DC from my garden, and using the blackout blanket idea, I was successful in not only detecting IC434 but also a small notch of black nebula protruding into bright nebula IC434. I wasn't using any filter! I feel reasonably high magnification may help in your quest for the horse head, as the sky background will be darker making IC434 easier to detect. Once youve found that, you should be able to see the HH with averted vision. (Its tiny!) It may be best to keep Alnitak outside the field of view!

That's pretty impressive Mike. How dark are your skies at home?

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49 minutes ago, Paul73 said:

All good advice so far. It should be possible with your Dob. John did it with a 12” in the UK where it is much lower....

 

Indeed I did and I've done it since with the same scope plus Astronomik H-Beta filter. It's probably the most challenging target I've ever pursued and observed in my years of observing. I'm very glad I've done it but to be honest it's a pretty underwhelming visual experience without NV technology to enhance things.

Here is my thread on SGL when I managed to see it, which might contain a few tips that might help:

And here is a very useful link which I found helped a lot:

https://www.skyhound.com/observing/archives/jan/IC_434.html

And the excellent Jeremy Perez page on this target:

http://www.perezmedia.net/beltofvenus/archives/000379.html

Best of luck with it !

 

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Its kind of underwhelming yes as John has mentioned, yet it does have a defining impact, as I had described - encountered as a velvet black thumbprint, which is easiest seen with averted vision but can be glimpsed / tricked into seeing (with medium aperture scopes) fleetingly with direct vision. Elusive but appealing, I feel that the traditional visual experience is quite satisfying - in the right circumstances and I have begun to gain an interest in pursuing dark nebula, an entirely new learning direction.      

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10 minutes ago, Stu said:

That's pretty impressive Mike. How dark are your skies at home?

I'm not sure how dark my skies are Stu, but mag 6 in the zenith is achievable on occasion. Looking at dark sky charts, there are much darker sites than mine, but locally, I'm shielded from much of the town's street lighting by a hill and woodland to my S/SW, high hedges to my E/SE, while NW to NE there are fields right to the horizon. The site though is low down and quite sheltered and is close to a river, which often gives me stable air, though often quite misty. Great for planets but not so good for dso's, except when the mists disappear. The town has also considerately switched off some of the street lighting along the M65 which dissects the town, so that's helpful. I can't complain about my lot as I've got countryside all around me, or within a few minutes walk in any direction. Moorland surrounds the towm just a few minutes drive away, and observing buddies such as paulastro who have equally good sites. Then Peter Drew and the Astronomy Centre is just a 20 minute drive away. 

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1 hour ago, mikeDnight said:

I'm not sure how dark my skies are Stu, but mag 6 in the zenith is achievable on occasion. 

Just interested to learn what evidence you have for this Mike?

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There are plenty of interesting objects to go after before the horse... it will tempt you and leave you frustrated!

good luck

PeterW

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Just woke up, it's Saturday morning here, so many thanks for all your advice while I slept!

It does sound as if I'm in with a good chance of seeing the HH from here, we live in a small village 500 metres up, surrounded by forest, with no street lights and have no near neighbours, in fact there are no lights visible here at night at all. The only drawback is the light pollution from Melbourne which is down below out of sight but which casts a glow from the west. Orion thankfully appears in the darker east. 

I have a Skywatcher 32mm Plossl on its way from FLO as we speak so will definitely give that a go next week, and if still no luck I will bite the bullet and order an HB filter.

It seems to be a bit of an addiction pursuing the HH once you start, and for such an unimpressive result too, are we all mad? 🤣

Edited by Geoff Barnes
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2 hours ago, Geoff Barnes said:

It seems to be a bit of an addiction pursuing the HH once you start, and for such an unimpressive result too, are we all mad? 🤣

Quite possibly mad Geoff but kind of a "nice mad" if you can have that :grin:

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It’s all part of the fun, Geoff! I believe I had an encounter with the HH last month. I was using an ES82 30mm, Astronomik H-Beta and my 10” dob. I chose that combination to get the biggest exit pupil I could, at the cost of a lower magnification (40x). I started at Alnitak and slowly moved up IC434. With averted vision the black notch appeared. It was totally against my own expectations to see it. I think, as others have said, transparency is the key. I was at my local dark site and multiple people commented on the lack of moisture in the air that night. I also think the slow movement of the scope helps too. Something moving catches your eye more easily plus you give yourself a chance of putting the target in the right spot for your eye to pick it up. I also tried a 20mm eyepiece after the 30mm without success so, for me at least, the large exit pupil seemed important. The 20mm gave an exit pupil of 4.3mm which should be in the possible range but possibly dimmed IC434 too much in the 10” dob with the H-Beta. I tried again for the HH two nights after that, same setup but the transparency wasn’t quite as good and saw nothing. I’m no less keen to see it having seen it once already! 

Edited by Littleguy80
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As a side note. The thing that gave me confidence that I’d seen the HH was the position of the two stars circled in the SkySafari screenshot below. They were obvious in the eyepiece and confirmed I was seeing the HH in the correct spot. That’s pretty much the FOV I had with Alnitak just outside  

07251416-52A4-40FC-A998-9FCFB2A97A90.thumb.jpeg.bc6ff21ce3ac3f9d1b060b497f13dd7f.jpeg

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Having some options to play with regarding exit pupil helps as well. The filters such as the H-Beta have optimum exit pupil sizes but sometimes what works is outside of that. I've found that an exti pupil of 4mm seems to work best under my conditions with my observing eye so eyepieces of 20mm-25mm seem a good choice. But do try others too - you never quite know just when and how things will come together with this target :smiley:

 

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Indeed, take exit pupil recommendation with a pinch of salt.

Detection threshold for particular person (and indeed, we are all different) depends on target brightness, sky brightness and also size of the target.

Filters reduce sky brightness while keeping target brightness the same (some filters even block some light from particular targets - depends on both target and filter, but are effective if they block more background light - they enhance contrast).

H beta is recommended as it darkens the sky the most while leaving background nebula (almost) at the same brightness. UHC filter will darken background sky less, but will also leave target at the same brightness (even more than H-beta, since there is also H alpha light there - unfortunately human eye is not very sensitive in that part of spectrum). Using higher magnifications (small exit pupil) will darken both sky and target - so you can use that to dial in "sweet spot" for contrast - this is where all debate of exit pupil (which one is best to use) comes from. It will largely depend on person, sky conditions and filters used. Most agree that 4-5mm is "sweet spot" with H-beta filter because it darkens the sky quite a bit and any further darkening will just darken the target. With different filters, or without one - things change in this regard. There is additional thing about magnification - human eye tends to be most sensitive in small brightness changes of a certain size - enlarge target too much it becomes too big in eyepiece and your eye will not be able to see it (for the same threshold contrast) - make it too small, again your eye won't be able to see the contrast. (For further detail on frequency vs contrast in human vision: https://en.wikipedia.org/wiki/Contrast_(vision)#Contrast_sensitivity, there is interesting low contrast image that shows this)

Luckily you have a great tool for trying out - zoom eyepieces are excellent to test which exit pupil / magnification works best for you, under your circumstances.

 

 

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Assuming appropriate conditions, without a H-beta filter the Horse Head nebula so far as my experience to date is concerned remains invisible, with a H-beta filter and applying an optimum exit pupil, approximately 4mm (as stated previously with a medium aperture scope i.e. 8" -14") it becomes apparent. The alternative to this is Night Vision technology, which besides being very (very) expensive, would depend whether you prefer those distant travelled photons reaching your line of vision and accepting a more challenging observation, or an electronically presented image. Incidentally a H-beta filter is equally effectively advantageous with smaller aperture scopes - on bright nebula such as the California, when a larger exit pupil is applied.

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It’ll certainly be an interesting hunt. It is nice to see that most of the advice is consistent (a rare occurrence on SGL 😁).

Simple eyepiece designs seem to do well. After many failures, I’d developed a bit of an obsession. Purely to chase the horse I bought 20&15mm TV Plossls, Lumicon (old spec) and Astronomic Hb Filters. The 20mm with a 5mm exit pupil at x80 with either filter works best for me.

It is also worth noting, that the HH will appear quite large in your scope. Mike’s “tiny” description was with a scope with a much shorter focal length.

Paul

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I do observe the HH with no filter in my 15" dob and yes the exit pupil's recommended by Paul,Scarp15, Littleguy80 and John are right on the money- too small and everything disappears, with filter and without. My Zeiss 25.1-6.7 zoom is a great tool to check all this. In the 15" f4.8 the 30 ES 82,21E,20mm Lunt and 17E all show the HH no filter and we can dump the 17E off the list with a filter. My favorite is still the 25mm TV plossl which showed me the HH first, but the "Super" 25 SW does fine too.

7 hours ago, Geoff Barnes said:

I have a Skywatcher 32mm Plossl on its way from FLO

You are on the right course Geoff and you just might need a good HB, the only one I'd buy currently is the Astronomic.

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7 hours ago, Geoff Barnes said:

The only drawback is the light pollution from Melbourne which is down below out of sight but which casts a glow from the west.

I get to see that glow above me every night...

Edited by TheMan
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11 minutes ago, TheMan said:

I get to see that glow above me every night...

I feel your pain TM. Melbourne is starting to rival Las Vegas these days for illumination at night.

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