PDA

View Full Version : Object of the Week, September 28, 2014 - NGC 6543



Howard B
September 28th, 2014, 08:09 PM
NGC 6543

Planetary nebula
Draco
RA 17h 58m 33s
DEC +66° 37′ 59.5”

Magnitude: 8.1
Size: 20”

1381

"On the evening of August 29, 1864, I directed the telescope...to a planetary nebula in Draco [NGC 6543]. The reader may be able to picture to himself...the feeling of excited suspense, mingled with a degree of awe, with which, after a few moments of hesitation, I put my eye to the spectroscope. Was I not about to look into a secret place of creation?

"I looked into the spectroscope. No such spectrum as I expected! A single bright line only! ... The light of the nebula was monochromatic, and so, unlike any other light I had yet subjected to prismatic examination, could not be extended out to form a complete spectrum...A little closer looking showed two other bright lines on the side towards the blue. The riddle of the nebulae was solved. The answer, which had come to us in the light itself, read: Not an aggregation of stars, but a luminous gas."

So wrote William Huggins in his 1897 memoir after being the first person to show that not all nebulous objects were clusters of faint stars that merely needed a larger telescope for resolution, a view held by many astronomers until this singular observation. In 1863, he and his collaborator W.A. Miller had been the first to spectrographically show that stars were made of the same basic stuff as the Sun, so this discovery cemented Huggins, and NGC 6543, in astronomical history.

Even without knowing the role 6543 played in getting modern astrophysics started, it’s a visual treat through just about any size scope. This past August I made this sketch at the Oregon Star Party that hints at the overall detail that’s available in 6543. I used magnifications up to 1210x because the image scale made it easier to see the overall structure. Unfortunately, the seeing wasn’t steady enough to reveal the helical loops seen by Uwe in his sketch with his 27 inch as seen at:
http://www.deepsky-visuell.de/Zeichnungen/NGC6543_27.htm

1379 1380

I did glimpse this intricate internal detail briefly on a nearly perfect night at Steens Mountain with my old 20 inch years ago, and I’ve observed 6543 on many occasions since then hoping to recapture that view. So far no luck, darn it!

I’ve also included this sketch made by H.D. Curtis at Lick Observatory that was made from a series of small photographs of different exposures using the Crossley 36 inch reflector in 1918. Although Curtis’ drawing has more of a corkscrew shape than my sketch, it’s more similar to my sketch than to the iconic HST photo at the beginning of this post.

1382

On the other hand is the faint, circular halo that surrounds the brighter part of the planetary in my sketch that’s also shown so prominently in the HST image as a series of concentric halos sliced by innumerable straight rays converging on the bright central star. Has anyone observed any of this beautiful detail?

Further out is the extended halo of 6543, which stands out impressively in a sufficiently large scope (i.e. the 90 inch Bok). The Bok clearly showed IC 4677 is merely the brightest part of this large, scalloped ring, which I’ve only been able to see half of in my 28 inch. IC 4677 is in the upper right part of the extended halo in this sketch of my view through the 90 inch.

1383 1384

Over the years I’ve consistently described the overall color of 6543 as a bright blue-green, especially at lower powers, but on several occasions it’s retained its color at higher power as well. My hunch is that this depends a great deal on the transparency of the sky.

My best views of NGC 6543 have always been without a filter, mostly to preserve the color but also to see the most detail. What's been your experience?

"GIVE IT A GO AND LET US KNOW"

Uwe Glahn
September 29th, 2014, 09:00 PM
Hi Howard,

you just mentioned my sketch, thanks for that and perhaps a little more words about my experiences with the inner bends and the outer halo.

Inner structures
The PN was my enemy for years. From the moment I saw a sketch of Frank Richardsen with a very good 20" under perfect seeing I tried to catch these structures. (Franks sketch shows very similar detail than mine years later.) I tried and tried and had no luck, the seeing was never good enough to see any structure within the inner part. Than one morning on an High Alpine place the seeing became steady (I remember very exactly the moment and place) so that I just could see the two brightest lobes with my 16".

16", 1028x, fst 6m5+, Seeing I-II
http://www.deepsky-visuell.de/Zeichnungen/NGC6543.jpg

Years later I had the luck to have a superb seeing on one of the best seeing places in Europe and could see and sketch what you linked with my 27".

27", 1172x, fst 7m+, Seeing I
http://www.deepsky-visuell.de/Zeichnungen/NGC6543_27.jpg

But how thought that maybe a 16" aperture is the smallest aperture for the inner structures is wrong - I had to change my mind also. 3 years ago a friend of mine started a try with his 12". The seeing was again extremely good so he could magnify 1000x. I was shocked, he was surprised, the main bend were visible without problems and the fainter inner structure was indicated clearly. Perhaps he can show his sketch later in this thread.

Halo
I don't remember what aperture was the smallest to detect the brightest Halo fragment IC 4677 but I think we could catch it with a 10". With 16" it always was an easy target. Not so the outer halo. I tried this with my 27" under very dark skies and could definitely not see it.

First time we could catch it was through Jimi's big telescope. Perhaps for me the most impressive observation at all with this instrument. The halo was there as it was never been away. It was a direct vision object with 6mm AP and NPB filter. With little care the halo flocked out in many knots and faint streaks. I could remember the view like it was yesterday. It must be a similar spectacular observation like yours with the 90". Until this date I thought that faint and big outer structures were not so sensitive of aperture but this is not right - the example of the M 57 halo in Jimi's telescope shows that on an other object.

ChristianR
September 30th, 2014, 04:58 PM
Hi Howard, Uwe,

the PN is indeed an outstanding object!

What makes it interesting for smaller scopes, such as my 12"/f5 dobson, is its surface brightness. You just pump it up beyond limits and see what happens...

As Uwe outlined, we had one of these really very rare occasions with excellent seeing conditions on the Edelweißspitze, Großglockner High Alpine Road, in October 2011.

Increasing the magnification to 1000 (which is usually meaningless for a 12" scope, I know), I couldn't believe what I saw in a first place. Beside the central star also different shells were clearly accessible!!

I took a sketch(*) and looked for a second observer to confirm the observation.

The result:
1386
Observing Location: Edelweißspitze (8400feet asl)
Observing Date, Time: Oct. 2 2011, 2am
SQML = 21,45 mag/arcsec*2, rel.Hum. = 92%, Temp: +37,4DegF, seeing: excellent
Scope: Dobson "Hofheim Instruments" 12"/f5
Magnification: 1000x (Nagler Zoom at 3mm & Barlow 2x),
no filter

(*): This was the point in time when I decided to purchase an equatorial platform for my scope....

Howard B
October 1st, 2014, 11:27 PM
Wow Christian, that's a magnificent observation! Instructive too, because it shows that the internal structure of 6543 doesn't need a really large telescope, only really excellent seeing conditions. And a keen eye. Your comment about this observation being the deciding factor in buying an equatorial platform put a smile on my face - I think high power observations sell a lot of platforms.

Frank Richardsen
October 4th, 2014, 03:12 PM
Hi all,

Indeed, I looked regular on NGC 6543. Cause of it's brightness there appear first nice details in my 5 1/2" Apo-bino. With 20" it' s an outstanding and irresistible object with a lot of details! Best view I had always with power from 800 to 1.000x, sometimes above. With it, no filters and good seeing come several shells out, cutting partly each other and showing faint signs of veinstructure. On N-side slightly asymmmetric by a small dent.
The drawing was created in a dry april night in the bavarian alps with very good seeing. The power was 1060x and no equatorial platform.
1391

Frank Richardsen
October 5th, 2014, 07:35 AM
Hi again,

little postscript: I agree with Uwe, concerning the halo fragment IC 4677. It was easy to seen in my 14 inch scope, but other details in the haloshell are being obscured with this aperture and also 20" under alpine conditions.
I had also the luck to observe it together with Uwe at Jimi's 48" scope! Uwe told it before, the halo was easy to detect by this aperture and the NPB. For me the fluffy structure over a wide field was the deepest impression of this object.