Object of the Week, March 25, 2018 - NGC 3242, the Ghost of Jupiter

Planetary Nebula
Hydra
RA 10h 24m 46.1s
DEC −18° 38′ 32.6″
Nebula magnitude: 7.7 (V)
Central star magnitude: 12.1 (V)
Size: 25’

Attachment 2957
Burness Ansell/Adam Block/AURA/NOAO/NSF


William Herschel discovered NGC 3242 in 1785, and described it this way:

“Beautiful, brilliant, planetary disk ill defined, but uniformly bright, the light of the colour Jupiter…”.

Much later, Admiral William Smyth described it as:
“From its size, equable light, and colour, this fine object resembles Jupiter.”

But the comparison only goes so far – there’s no chance anyone who’s seen Jupiter would mistake 3242 for any planet, much less the brighter and completely different looking gas giant. Unfortunately, this confusing nickname contributed to the ongoing use of the misleading label “planetary nebula” for this class of object.

Although that can be an interesting discussion all its own, it's not the point of this post. I chose spectacular NGC 3242 for this week’s object because I’ve rarely had a good look at it – poor weather and its southerly declination consistently get in my way - but I’ve still managed to get a few decent observations, most notably with my 28-inch and Jimi’s 48-inch scopes.

My most satisfying look through the 28-inch was in April 2012 from Likely Place, California. My notes:

“It’s been a long time since I’ve had a good look at 3242 but this view makes up for lost time. Excellent view at 695x showed some detail at each end of the inner ring, and the faint outer halo was evident at 155x. The annulus between the inner ring and the bright perimeter is brighter on both sides of the middle and darker on the ends. The central star is bright and easy – and seen through the h-beta filter! Dim, but definitely seen, as was the inner ring. 21.76 SQM.

Attachment 2953 Attachment 2954

Three years later the view through Jimi’s 48-inch was, of course, even better:

“The Ghost of Jupiter is looking marvelous at 813x – a distinct rim to the perimeter is obvious as are the two ansae on the inner annulus. The outer halo is also well seen as is a dark “moat” between the inner annulus and the rim. An added plus are the two direct vision galaxies in the 488x field of view!" (MAC 1024-1840 and 1024-1842)

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What strikes me about both of these observations is the wonderful, and somewhat spooky symmetry of 3242. It barely seems real! The outer halo was surprisingly easy to see, perhaps the brightest outer halo of any planetary. These eyepiece sketches don’t capture the subtle gradations of 3242 all that well, and it has a wonderful silky-smooth texture that's impossible (for me) to capture in a quick pencil sketch.

My notes don’t mention color, and strangely only one of my other observations mentions its strong greenish-blue hue. I think that’s because I quickly went to high magnifications to study the internal detail and I forgot about the color when writing my notes. Does that happen with anyone else?

"GIVE IT A GO AND LET US KNOW"

Great choice. I can contribute a very small aperture drawing.

4.3", 96x, 25' field, 2003 February, Kerepes, Hungary ("Ny" is West)
Attachment 2958

My notes read: "Very bright beautiful bluish planetary. Slightly elongated (PA 140). The central star is visible but the contrast is very low due to the bright nebula. The western part is slightly brigher and a low-contrast arch is visible in each end."

Howard, I know what you mean with forgetting color. I always forget to look for it / note it (and then forget what I had seen). But not in the case of NGC 3242. I think the Ghost of Jupier is perhaps the most vividly colored deep-sky object in a 4" telescope.

There is a huge outer halo around it. See e.g. Don Goldman's photo:
https://astrodonimaging.com/gallery/ghost-of-jupiter/
I have never attepted it.

My notes with my 20" from 21 Feb 2015 read:

"At 83x a vividly green sphere. At 320x and most notably at 545x a large, green sphere with a central star and an ellipse ending in pointed tips. It resembles an eye surrounded by a sphere. I tried again at 83x and the ellipse is visible at that magnification as well."

So I did see the green colour at high magnification.

This is a favorite, and I revisit when I can. My most memorable observation was from a couple years ago at a local not-so-dark site with my 20-inch. Conditions were decidedly non-ideal, with gusty winds, average to poor transparency, and occasional sweeps of cloud moving through. Through the night my SQML ranged from 20.50 to 19.40 to 20.93 – as crazy as the weather.

NGC 3242: PN in Hya: NGC 3242, Ghost of Jupiter, PN: Visible in the 80mm finder as a blinking star. Amazing in the scope! Best view at 333x without a filter, but I did try 553x which enhanced some details in rare moments of seeing. All features in the PN had a light blue / teal color. The central star sat serene in the middle of a ring which was visibly tubular. The gap between this ring and the star was only slightly darkened. The whole was enveloped in a large semitransparent outer shell with defined but oddly soft edges. Moments of still seeing at high power hinted at annularity of both inner ring and outer shell, and some bright filaments like electric bolts running between the outer shell and the inner ring. Imagine what this looks like on a good night.

My best view of NGC 3242 was the night of November 17th, 2005, while observing with a group of 16 folks, when we rented the 82”, F13.7 Cassegrain, 812X using a 35mm Televue Panoptic, yielding a 5.5 arc-minute FOV at McDonald Observatory for the weekend, just up the road from Jimi's place. We were using that telescope's lowest availble power. Here is what I wrote at the time...

"NGC 3242, Ghost of Jupiter, Hydra

Well, this might have been the best object of the weekend, Saturn notwithstanding. It was just as I remembered it to be when I viewed it through this same telescope in 2000, during the TSP. This PNe has a large slightly oval shape and shows multiple shells, with a bright central star, several other observers used the word "bagel". The innermost ring is small and dark, and had a purple-tinged outer edge. The next shell outwards is a bright crepe-like ring, shocking aqua in color. This is followed by a broader ring that is distinctly salmon or pink in color, my notes call it a "filling", and virtually everyone saw it this way. Lastly was another aqua ring, thinner than the pink ring, and not quite as vibrant in hue as the other aqua ring; it is almost perfectly uniform in width and looked like a racetrack. Curiously, the real-time view in this telescope looks nothing like any picture of this object that I have seen, and I've searched extensively to find a picture that even slightly resembles what I saw. None at all. To see this, I guess you need to book a night on the 82"..."

Hi All,

Surely one of the most impressive PNs. Here is my sketch, Obsession 20", Southern Alps.
The inner part has been observed in a good, but not exceptional night, SQM 21.63. The colour of the PN was blue-greenish.

The halo has been observed, ten years later, on an exceptional dark night: SQM has been measured at 22.00 by two different observers with two different device. Such a value is totally rare in my observatory in southern Alps.
The color was blue, with no hint of green, estimated C130 / S30 in the usual concentration / saturation scale.

Attachment 2959

Report of the inner part: http://www.deepsky-drawings.com/ngc-3242/dsdlang/en
Report of the halo: http://www.deepsky-drawings.com/ngc-...017/dsdlang/en

Clear skies
Bertrand
http://www.deepsky-drawings.com/dsdlang/en/

I must say that it is A awesome site to see the ghost at high power 800X to 1200X it's one of best objects to see pink color in. But most observers do not know that there's a outer shell that is beyond the high power drawings you see above. I like to show it to people after a high power view. The best eyepiece combination that I have found to see this elusive shell is a 24mm Brandon eyepiece that gives 203X with a 6.0 mm exit pupil. I also use a DGM NPB nebula filter. This combination is the best I have found so far to observe this faint shell.

Attachment 2960

This is the best image I could find that shows the outer shell.

It is really cool to see in the eyepiece just how large this nebula is compared to the usual high power view.
I would like to here from anyone if they have seen this fant outer shell.

Hi Howard,

I observed this nebula with my 12" Dobsonian 3 years ago. At 275x magnification I saw a bright area along a crescent at its western side. The nebula was fainter outside this region. Additionally, I saw a halo when using an O-III filter and averted vision.
This is one of the few deep-sky objects my eyes can see color in. At 47x magnification, without filter, the nebula appeared bluish-green. At 84x or more magnification (3.6 mm or less exit pupil diameter), I couldn't see color.

Clear skies

Robin

A very beautiful object Howard, great choose. I'm wondering that this one wasn't an OOTW yet.

To the object. An important detail to add is the outer halo. The above mentioned shell is only the small inner shell. Another much larger outer shell was discovered by Bond (1981PASP...93..429B) in 1981. The shell is already visible in the POSS prints.

DSS 45'x45' blue
Attachment 2963

Some astrophotographers already catches the halo and shows brightness in [OIII]

Marco Lorenzi, 140mm TEC, HaOIIILRGB (small, rotated)
https://www.glitteringlights.com/Ima...ulae/i-NH4CpPn
Attachment 2964

Visually the PN suffers from its low position in the sky from Germany. Details and the halo are different to resolve.

sketch: 16", 600x, no filter, seeing III, NELM 6m5+
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I went to La Palma (29°N) to catch more details of the inner structure and the two "companion" galaxies.

sketch: 20", 484x - 645x, no filter, seeing II, NELM 7m0+
Attachment 2966

The inner and outer halo of course needs other power and equipment. I used powers of 114x (EP 4,4mm) for the outer halo and 194x (EP 2,6mm) for the inner halo + an [OIII] filter. I noted for the outer halo "already suspected without filter, strong reaction with [OIII], brightest part steadily visible with averted vision, brighter and better defined rim towards the PN, faint extensions to the south", for the inner halo I noted "bright and direct vision, 6' large, small knot to the south"

sketch: 20", 114x-194x, [OIII], seeing II, NELM 7m0+
Attachment 2967

Thanks Uwe and Peter, I didn't know about the huge arc of the outer halo, and I'll give it a go the next time I can!