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Object of the Week,October 14, 2012 - Cassiopeia A SNR
Cassiopeia A
Supernova Remnant
RA 23 23 26
Dec +58 48
MAG: ? My guess is approximately 14th magnitude.
An article about little known and seldom observed supernova remnants in issue 63 of Amateur Astronomy magazine (pages 17–19) caught my attention before the 2009 OSP. It’s the fourth article in a series on the subject written by William Gates. Bill is a terrific observer but what really caught my attention was his report that he was able to observe a shard of the Cassiopeia A SNR as an relatively easy object in his 9.25 inch SCT equipped with an OIII filter. Wow!
Until then I'd always had the impression that Cas A was essentially invisible at optical wavelengths to all but the largest optical telescopes and that only radio and infrared telescopes could get a good image of it. Checking Wikipedia I found a quote to that effect:
“Cassiopeia A (Cas A) is a supernova remnant in the constellation Cassiopeia and the brightest astronomical radio source in the sky… Despite its radio brilliance, however, it is extremely faint optically, and is only visible on long-exposure photographs.”
http://en.wikipedia.org/wiki/Cassiopeia_A
I’m happy to say that Bill was right and that Cas A is indeed visible in amateur sized telescopes from a dark sky site, and that at least some of its structure can be seen. Heck, it’s easier to see than some NGC objects. My best view to date is from the 2011 OSP under a 21.71 SQM sky when Cas A was near the meridian. My pencil sketch below and its inverted version show what I saw during an hour and a half of observing that night, which was a bit more than I saw in my first observation from 2009 when the skies weren't quite so dark and transparent.
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I used 220x to 355x with the NPB filter on my 28 inch f/4 Newtonian for the best view, but Cas A was easily visible without a filter. My old Lumicon OIII filter dimmed the view too much for my liking but showed more than the non-filtered view.
As far as I can tell Cas A isn't listed in Megastar or Sky Tools 3 Pro but is plotted in Uranometria. I've found that star hopping from M52 to the Bubble Nebula (NGC 7635) and then along a ragged line of faint stars to Cas A is a relatively easy way to get to the right spot.
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My goal now is to detect a piece of the southern arc, which may be near the limit of my scope under ideal conditions. The DSS image here hints at its difficulty – should be a piece of cake for Jimi’s 48 though.
So remember,
"GIVE IT A GO AND LET US KNOW"
GOOD LUCK AND GREAT VIEWING!
