Quote:
Originally Posted by mandragara
Hi,
I'm up in the Blue Mountains with a 12" f/5 Dob and want to try and see the Horsehead this season.
I own a 30mm 82deg ES eyepiece and was thinking of getting a 2" Astronomik H-beta filter to use with it ($300 at Bintel).
However, it dawned on me that I could also just get a 1.25" filter for $150 and hunt down a TeleVue 32mm Plossl to use it with for about the same price as the 2" filter. Currently my longest FL 1.25" eyepiece is a 24mm 68deg ES but I think I want the bigger exit pupil.
Do you think the extra FOV from the 30mm 82deg + 2" filter would improve my odds of seeing the Horsehead? Or would I be better off looking through a narrower FOV made of TeleVue glass?
I already have a 1.25" Astronomik O-III and UHC and a Kson brand 2" O-III filter.
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Hi Richard,
There's a few things to get in order to observe the Horsehead (B33) in "threshold" sized telescopes. A 12" Telescope is borderline under most conditions, but it is doable when it all comes together. In fact when everything is favourable it has been observed by people in telescopes down to 4"; but that isn't the norm. The Astronomik UHC filter, while not quite as good as a H-Beta on B33, will certainly help a lot. I wouldn't race out and buy a H-Beta filter in the hope of seeing the Horsehead, because the telescope is borderline in any case and you won't use the H-Beta on many other targets at all. About 15 or 16 years ago Glenn Dawes (another experienced observer) and myself spent about 2 hours trying to find the Horsehead in a 10" telescope under pretty good skies at a South Pacific Star Party without success.
Here's a checklist of things to steer you in the right direction to achieving success with your 12" scope
1) Dark Skies
2) Darker Skies (I doubt Blue Mountains will cut it, go West)
3) Give yourself at least an hour after full dark, to get properly dark adapted. Don't look at bright targets like Jupiter/Saturn. etc and then jump to the Horsehead. That won't work. Stay away from bright things for a good while before you try for B33.
4) Clean Mirror
5) Astronomik UHC Filter
6) Well cooled and collimated telescope
7) A "decent" eyepiece giving an exit pupil of 3mm to 4mm. In your scope that's a 15mm to 20mm eyepiece. The smaller exit pupil improves contrast and is far more important than a wider FOV.
8) If you can see the Flame Nebula (NGC 2024) there's a reasonable chance you will be able to see the Horsehead (B33). If you can't see the Flame, don't waste your time on the Horsehead.
8) Use Alnitak (ζ Orionis), with averted vision, to orient yourself and figure where you need to look for the Flame and the Horsehead and then push Alnitak out of the FOV. You won't see anything whilever Alnitak is in the FOV unless you have a 20" or larger telescope.
9) It's very dim and unimpressive as a visual target. The Horsehead (B33) is actually a dark nebula in front of a bright emission nebula (IC434) which creates the visual appearance of the Horsehead. Unfortunately IC434 isn't so bright in average amateur telescopes and is barely visible above the background sky brightness, which makes the Horsehead very difficult to see. In my 14" telescope it appears as a barely discernable "notch" against the background nebula, which itself is very difficult to detect.
Now here's the rub and why "some" people might not ever see it. IC434 emits it's light towards the red end of the spectrum. People with a low sensitivity to red light just cannot see IC434, which means they won't see the Horsehead. One of my very skilled observing buddies is in this category. He can't see it in a 25" telescope.
Here is a link to an image which shows the relative positions of The Horsehead and the Flame in relation to Alnitak
Good Luck !!
Cheers
John B