Re: [APML] NGC6357 in Scorpius - Schmidt Camera Shot

[Ray Butler <ray.butler@nuigalway.ie>]

Chris Schur wrote:

>Hi all,
>
>Yes, another film shot to ponder.  All three objects just fit in this field,
>which is 6.5 degrees wide.  
>

Another fine shot! I like comparing the colours of emission nebulosity. 
Bright nebulae which are nearer to us and little obscured by dust tend 
to be pink, the combination of red H-alpha at 656nm and blue (UV) OII at 
370nm. Nebulae like those in your picture, which lie behind significant 
veils of dust, lose nearly all the OII to interstellar reddening. So 
they appear much redder - maybe just a little orange, from the greenish 
OIII and H-beta which make it through the dust, albeit attenuated. The 
Lagoon and Triffid nebulae, just a few degrees away, are quite a 
different, pinkish colour.

There is a beautiful David Malin plate of a small field in the southern 
Milky Way, showing two large bright nebulae which appear to be adjacent 
in the sky, but having very different colours. The reason is that one is 
more distant and reddened. Here it is: 
http://www.aao.gov.au/images/captions/aat038.html

>With schmidt shots its always important to have
>the edges of the frame align with the cardinal points.  
>

Just wondering, why is that important with Schmidt shots (as opposed to 
any other instrument)?

Ray "probably there's an obvious reason, but I have sleep deprivation as 
an excuse" Butler

>Anyway, let me know
>what you think of this new one:
>
>http://www.schursastrophotography.com/filmimagepages/ngc6357.html
>
>
>Clear Skies,
>
>Chris
>
>---
>
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-- 
Dr. Ray Butler
Lecturer, Physics Department & Computational Astrophysics Laboratory,
National University of Ireland - Galway, 
University Road, Galway, Ireland. 
Web: www.nuigalway.ie/physics/ 	Email: ray.butler-AT-nuigalway.ie 
Tel: +353-91-493788 		FAX: +353-91-494584

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