Obs report: horsehead nebula, Jan 12 2008

[PhilW]

Last night we enjoyed an exceptionally transparent night at Heathcote, the Astro Society of Victoria's deep sky site north of Melbourne. It enabled me to get my first clear, definite views of the horsehead nebula, as distinct from the 'averted imagination' views I've had in the past.

My understanding is that suitable eyepieces for viewing the horsehead produce around a 5mm exit pupil, with high light transmission and a moderate field of view (so the glare of zeta orionis can be kept out of the field). It also needs an H-beta filter, or failing that a general nebula filter. We tried five different eyepieces that met the above criteria, and the results are ranked below.

Scope used was a 14" F/4.6 dob. It has a Suchting mirror, plenty of cooling, flocking, and a wire spider. Eyepieces were used with an Astronomik nebula filter.

The eyepieces tried, in order of effectiveness, were:
1) Zeiss 25mm ortho triplet, kindly on loan from Stephen65. This eyepiece produced by far the clearest and most contrasty views of the object, as well as the best views of NGC 2024 nearby (the flame nebula), and also the Rosette nebula in Monoceros
2) Pentax XW 20, also temporarily liberated from Stephen's extensive eyepiece collection
3) 25mm volcano top ortho
4) 20mm Kellner of uncertain provenance
5) Meade 25mm super plossl.

The horsehead was quite clear in both the Zeiss and Pentax eyepieces. In the other eyepieces it was visible, but required averted vision.

Phil

[edwardsdj (Doug)]

I'd love to see this object visually. Thanks for the heads-up on the eyepieces to use

[Tannehill]

When Phil announced he had it, I was convinced he was delusional. He had been muttering about flock this and flock that (pretty sure that was what he was saying.......). Anyway, I'd been on a 25" at Coona with a UHC and NOT seen the thing even knowing it was there, so it was fairly impressive that this 14" pulled it in. Combination of the top end mirror and it's condition (collimated, cooled, etc) the sky, and the EP, as Phil suggested.

I might just check that Zeiss out....since I can see the HHN back home in the US in a few areas lacking city sky glow...

s

[Stephen65]

I didn't think you could even see the Horsehead visually, but last night we did. It presented as a darker than dark patch as compared with the surrounding very faint nebulosity.

It was exceptionally transparent night made more pleasant by the stillness and mild warm night. Another highlight was seeing NGC1049, the extragalactic glob in the Fornax Dwarf. I also tracked down all the globs associated with the Canis Dwarf, some planetaries and a few of the Messier open clusters that just rose above the Northern horizon. The Flame Nebula also looked very good and the nebulosity in Eta Carinae was very vivid.

[ngcles]

Hi Phil,

Congrats and well done mate. I assume the Astronomik filter is of the "UHC" variety -- ie a narrowband filter that permits both the doubly ionised Oxygen lines plus the H-Beta line. If so, it is a quite suitable filter for the purpose as most of the Horsehead Nebula (IC 434 & Barnard 33) is in the H-Beta line.

The smallest scope I've seen it in is 25cm and I've good reason to believe that in _perfect_ (and I really mean perfect) conditions 15cm will do the trick -- barely.

I always said I'd never buy a H-Beta filter because it has so few applications, but I took the plunge about 18mths ago. Let me tell you the improvemennt it makes on the Horsehead is huge.

In 31cm it goes from being a marginal threshold object to merely "difficult" using the H-Beta, and in 46cm, it is _bleedingly obvious_ direct vision -- no problemo with the filter. A UHC helps a lot, but the H-Beta is like flicking a light-switch on. My favorite view is with 20mm T2 Nagler at x111 with a 4mm exit-pupil and H-Beta.

Again, congrats and well done.

Best,,


Les D
Contributing Editor
AS&T

[Stephen65]

Yes, it was the Astronomik UHC filter.

[PhilW]

The filter was also on loan from Stephen.

I have a DGM Optics NPB filter permanently mounted to the scope on a filter slide. I believe it has a similar absorption profile to the UHC, and would have been equally suitable. The problem was that the nice Zeiss required a lot of focuser in-travel, & I couldn't get the eyepiece to focus with the slide in.

Many thanks for your information Les. You've given us more stuff to try next time.

Phil