How do i find the Rosette Nebula?

[PETER_TRA]

On Saturday night ( no moon ) I was using my 10inch Dob 50km South West of Melbourne . I found the position of Rosette Nebula on Stellarium but when i pointed my scope to that part of the sky i could'nt find it . I searched for a while but no luck . Is it visable using a 10 inch Dob? Any hints on finding it ?

[mental4astro]

The Rosette Nebula is both an enormous nebula, and a real, real challenge to see. I managed my very first sighting of it just one month ago.

In a nutshell, you need to be in a dark site, a low power eyepiece, and an OIII (oxygen three) or an UHC (ultra high contrast) filter. If there is any light pollution in its direction, it is impossible visually. An OIII or UHC filter will kill the background skyglow and allow through the faint glow of this emmission nebula. The low power eyepiece is to maximise the amount of light getting into your eye, where too high a magnification will darken the overall field of view and will further reduce your chance of seeing it.

Now, its size. It is BIG. Once you've located its associated open star cluster, which will close to fill your field of view, the nebula will extend upto the same size as your field of view all the way around this cluster like a giant faint thick ring!

With a 10" scope, you could well be able to make out the many dark pillars and maybe Bok Globuals that permiate through this enourmous nebula. These dark features are where protostars are forming, awaiting further condensation of gas and dust to trigger their thermo-nuclear fire. You will need an OIII or UHC filter to have any chance to see them though, and patience.

Mental.

[gpb]

A question for you Mental, any chance of seeing any colour (of the nebula) using any of those filters you mentioned?

[Blue Skies]

AN OIII filter washes everything to green, it kind of kills any natural colour that's there.

I have an 8" dob at in a 25mm ep (x48) I can fit a quarter of the Rosette in. That should give you some idea of how big it is. With a 10" you'd probably be looking at a slightly smaller area of sky, depending on the eyepiece being used, but I wouldn't expect to see it all in one go. (Not unless you've got a scope with a very short focal length and hence a very wide field of view!)

[mental4astro]

The green you mention, Blue, is a result of the low level of light rendering our colour vision useless. It isn't a "wash out" as such. These filters transmit the wavelengths of light that these nebulae glow at. If our eyes where more sensitive at these low levels, we would actually see red and blue - both colours our eyes are least sensative to.

If you want to see "natural" colour in nebulae, you'll need to first start with a scope larger than 16", and begin with the Orion Nebula. I've started to glimpse soft pink structures in my 17.5" in it.

You can see some faint colour in some planetary nebulae in smaller scopes, like the PN NGC 3918 the "Blue Nebula". Its distinct vivid blue is noticeable in scopes as small as 6". It isn't a large object, and something around 100X is needed to make out its disk to distinguish it from surrounding stars.

[Brian W]

Not sure that I agree with you Alex. Both my wife and I have seen colour in M-42, The Ring nebula, Eta Carina, The Seven Sisters and others in both our 4.5" reflector and our 8".

Of course it requires a great night but colour can be found with smallish scopes. At least in our experience it can.
Brian