Quote:
Originally Posted by Bobbyoutback
Fancy be able to see the horse head with direct vision through your 25" I've never seen it in my eyepiece .
And as you said 410% more light then a 12" makes the magic happen 
Regards
Bobby . |
The Horsehead is a bit of an enigmatic target. The Horsehead image is created by a dark nebula (Barnard 33) sitting in front of an emission nebula which is a massive HII region (IC434) which actually illuminates it. HII regions emit a lot in the upper red end of the spectrum. Different people have different sensitivities to red light under dark adaption. Those whose vision doesn't extend as far into the red will have a lot more trouble observing the Horsehead than people who can see deep into the red. This was demonstrated at the IIS Astro Camp at Lostock in 2007. Andrew Murrell had his 25" Obsession set up beside my 18" Obsession and we were running sky tours with a group of about 15 to 20 people sharing the views in both scopes. Someone asked to see the Horsehead in my 18" Scope, so I put it in the FOV. It was unfiltered, but conditions were excellent and I had no trouble seeing it. Our friend Gary was helping us with the sky tours and went to the eyepiece for a look. He said to me, "I can't see anything". I was quite surprised at this as Gary is a very skilled observer and I thought he would see it easily. I called out to Andrew to put "the Horsehead in the 25 inch" which he did. I then went to the eyepiece to compare the view between the 2 scopes. Unfiltered in the 25" it stood out to me like the proverbial. Gary went to the eyepiece and couldn't see anything. I was perplexed at this knowing his observing skill and experience. About 6 months later I read about different human sensitivities to red light and immediately realised that this was the reason Gary couldn't see the Horsehead, but Andrew and I could. That particular night about 30% to 40% of the people around the scopes could not see the Horsehead.
Cheers,
John B