NGC 6543, the Cat's Eye Nebula, presented an interesting challenge for us this month. Our Challenge participants weren't expecting their views of NGC 6543 to look anything like the Hubble images above, but check out their images, sketches, and observation reports below.  To check out this interesting object yourself, look for NGC 6543 in the constellation Draco using the Skymaps below.

Click on the images for a larger view

NGC-6543 or Caldwell 6 is more popularly known as the Cat’s Eye Nebula.  This one is going to be a real challenge for those with smaller scopes.  At 70X it appears as an out of focus fat star.  It will be easy to miss if not looking carefully.

William Herschel discovered this fine planetary in the constellation of Draco in 1786.  William Huggins was the first to study the spectrum of planetary nebulae and in 1864, discovered that it consisted of hot gas and not stars.  It is one of the most studied planetary nebulae.  Its apparent size can partially be attributed to its 3,300 light-year distance.

With a magnitude of 9.8, it is well within the reach of even 60mm scopes.  However because of its size, it will take significant magnification to sort it out from the background stars where details can be seen.  With larger backyard scopes and high magnification, many details can be seen, though vaguely and nothing like those Hubble photos.

Though the central star is around mag. 11, it can be hard to spot against the brightness of the nebula, especially with scopes below 12”, though it has reportedly been seen with scopes as small as 4”.

Speaking of Hubble photos, by doing a quick search, many spectacular photos of this nebula may be found, like those at the top of the article.  The colors and shapes within it seem endless in variety.  As visual observers though, unless one has a 30” or larger, the real challenge is to just see a few of these details like the central star, the visual bluish color of the nebula, or maybe the two most prominent lobes.  Give it a try.  It will definitely hone one’s observation skills.

This month, we asked our Challenge Participants to:

  -  Describe a wide field view of the nebula.

  -  Describe what they could see at the greatest magnification at which they could see detail.

  -  Observe and describe the two lobes of the nebula?

  -  Observe and describe the halo that surrounds the nebula?

  -  Observe and describe the central star?

  -  Observe and describe the galaxies that are in the vicinity of the nebula?

Observations/Drawings/Photos

Roger Ivester: LVAS Member from Boiling Springs, North Carolina

NGC 6543, the Observers Challenge for July has always been a favorite of mine.  It was the Finest Deep-Sky Objects by James Mullaney that first brought this most interesting planetary nebula to my attention.  I feel it is most unfortunate that I do not have any notes of that first observation from many years ago.  My first recorded notes were made in 1994 using my 10” reflector.  The following is a description from that night.  All observations were made from my moderately light polluted backyard, located in Boiling Springs, North Carolina.

This planetary is bright and easy to locate with the 10” using 57X.  It presents a bright, mostly round, bluish disk.  Could not see the central star.  When using direct vision, the outer nebula seemed to disappear, leaving only the core visible.  This effect was rather significant – the color is more vivid at lower magnification.  The blinking is very noticeable at 57X, but diminished at 190X.  This effect is very similar to that of NGC 6826, known as the “The Blinking Planetary” (see Roger's NGC-6543 Sketch and Notes below).

Roger's Sketch of NGC 6543 at 190X

My observations of the past couple of weeks were made using both my 4” refractor and 10” reflector.  It is surprising, but the small refractor presented the planetary almost as well as the 10”.  The bluish color was obvious at all magnifications.  The mostly N-S elongation was best seen at higher magnification.  The texture appeared very even, with high surface brightness.  At lower magnification, the edges seemed sharp and well-defined, but when using 167X and averted vision, the edges became less smooth and with some irregularity.

The view through the 10” presented a blue N-S oval situated a few minutes ESE of a mag. 8 star.  A fainter star to the north created a triangle with the nebula and the brighter star.  The texture appeared mostly even and the central star could not be seen when using magnifications from 57X to 266X.

When using my 4” f/10 Meade Schmidt-Cassegrain, it presents a very similar view as that of the 4” f/9.8 refractor.  The shape was mostly round, with a hint of elongation when using averted vision at 167X.  The bluish color was recognizable and the texture appeared very even, the edges were well defined and rather sharp.  The high surface brightness of this object allows for a decent view even with a first quarter moon.

Fred Rayworth: LVAS member from Las Vegas, Nevada

I have seen it many times over the years.  In 1984 through my 8” f/9.44 reflector, I saw just a nice small planetary, but not the central star.  In 1993, with my 16” f/6.4 reflector at 70X, I saw a beautiful greenish-blue disk and with averted vision, the central star.  The next year, I saw it again with the same setup but it appeared solid.  In 2005, with the same setup, it looked like Uranus.

On 5 July, 2010, with my 16” f/4.5 scope, I recorded my most detailed observations under much higher powers.  The sky conditions were conducive to much more detail and I was able to magnify it substantially.  The night was hot with only an occasional gust of wind.  This was a six bottles of Gatorade night!

Fred's Sketch of NGC 6543 at 70X

It appeared very small.  At 70X looked like a bluish-green planet.  The color was washed out at higher powers (see Freds NGC-6543 70X above).  At 229X, the central star popped out.  Could sometimes see it directly, other times with averted vision.  At 70X it looked round. However, at 229X it started to look more oval.  The center was still filled in but the central star stood out.  At 390X, saw the central star directly.  Still filled in but much less and could tell a difference in intensity between the edges and the center.  Edges flaked just a bit.  Couldn't see the lobes directly but with averted vision, just caught a glimpse that something was not quite right.  I also noticed a slight haze that extends beyond the edge of the main nebula (see Freds NGC-6543 390X below).

Fred's Sketch of NGC 6543 at 390X

Rob Lambert: LVAS member from Las Vegas, Nevada

This month's Observer's Challenge, NGC-6543, the Cat's Eye Nebula, was probably the most difficult for me as far as teasing details out of the object.  It is a very small object, and I wasn't sure I had it in my sights until I compared the image I was seeing with star maps and other photos of the area.  At approximately 33X, it mostly resembles a fuzzy star, with no detail at all (see ST120 image of NGC 6543 below). At this magnification, there were no halos or rings or any definition of features that could be distinguished from the fuzzy object.  The achromatic ST120 just wasn't able to resolve the object sufficiently to even recognize it without comparing with other photos.

Image of NGC 6543 captured with Mallincam through an Orion ST120 refractor

Because of the initial size of NGC-6543 through the ST-120 with the Mallincam at f/2.5, I decided to forego a focal reduction and attempted to locate the object in my 10” LX200GPS.  Even at 300X, it doesn't begin to reveal the detail seen in much larger telescopes.  It did, however, begin to reveal a single thick ring and even what I thought to be its central star.  Or, it may have been just the greater concentration of matter surrounding the central star (see LX-200 image of NGC-6543 below).  My wife would appreciate its teal or greenish-blue color. It is easy to tell that the object is longer on its north-south axis and it has a tail-like appendage protruding from its northern end.  In higher resolution photos, this corresponds to the brighter region of the northern lobe.  I was not able to see either of the two inner lobes or any of the concentric rings of the nebula's halo that are visible in Hubble images.

Image of NGC 6543 captured with Mallincam through 10-inch LX200GPS

The Cat’s Eye seems to be sufficiently bright to support greater magnification.  The next time out, hopefully at the Great Basin Astronomy Festival, I'm going to attempt observing it at 450X and see if I can tease out some more detail. I'll hopefully have three nights to concentrate on future and past Challenge objects.

Gus Johnson:  LVAS Friend from Maryland

NOTE: We welcome Gus Johnson from Swanton Maryland.  He is shown standing beside the 1910, 11-inch Brashear refractor, owned by the AAAP in Pittsburgh, Pennsylvania.  Gus has been an amateur for many years and was the visual discoverer of a supernova in galaxy M-100, in April, 1979.  The first supernova in modern times to be discovered visually was SN 1885A in M-31.  It was discovered by Hartwig, a professional astronomer at the Dorpat Observatory.  The first visual discovery of a SN by an amateur was by Jack Bennett of South Africa in July 1968.  In April 1979, the second SN discovery by an amateur was made by Gus Johnson of Maryland, USA.  Gus was using an 8” reflector, and located the SN before maximum brightness of around mag. 11.  We would like to thank him for being a contributor to the Challenge and look forward to his participation in the future.

NGC-6543:  Almost overlooked as a slightly out-of-focus star using a 6” at 59X.  118X showed it to be round and pale blue 10-12-79.  On 8-12-90 through my 4 ¼” at 38X, I saw it easily as a star that hazy night.  At 63X, it showed a solid disk, bluish.

Buddy L. Barbee: LVAS Friend from North Carolina

This observation was made Thursday, May 6th 2010 while at the Mt. Airy Granite Overlook, in North Carolina on the Blue Ridge Parkway near mile post 203.

I used my Orion XT-10i Dobsonian with a Tele-Vue 5mm Radian eyepiece that gave me a magnification of 240X.  The night was slightly above average in both seeing and transparency, with low winds and humidity. The temperature was a mild 65°.

Buddy's Observation Notes for NGC 6543

This small planetary nebula was presented as a bright bluish oval with high surface brightness, and a hint of brighter inner structure.  This inner structure was only seen intermittently.  The inner structure appeared as a brighter elliptical shaped line, whose visibility came and went as the seeing changed.  There was no central star visible on this night.  In retrospect, I think that maybe I should’ve used a filter to bring out this detail.

Other Notable Observations

The Night Sky Observer’s Guide, Vol 2, Spring & Summer, George Robert Kepple and Glen W. Sanner, Willmann-Bell, Inc.

In 4” – 6” scopes has a bright, small disk   with a greenish cat’s eye tint. In 8” – 10” scopes has a bright small round greenish disk surrounding a mag. 11 central star.  Averted vision reveals a fainter outer haze that is more conspicuous on its NE and SW. In 16” – 18” scopes, bright bluish green disk which provides contrast to the yellowish central star.  Inner halo elongated.  The hole in the center is more evident.

Observing Handbook and Catalogue Of Deep-Sky Objects, by Christian Luginbuhl and Brian Skiff, Cambridge University Press

This bright planetary is visible in 6cm (2.4”) as a star-like spot ESE of a mag. 8 star.  Clearly discerned in 15cm (6”).  No details but outline is somewhat elongated, especially in 25cm (10”) and the outline is not symmetrically oval.  N end is rounded while S is more sharply tapered but diffuse.

Burnham’s Celestial Handbook, Volume 2, by Robert Burnham Jr., Dover Publications

A small bright planetary nebula located almost exactly at the north pole of the ecliptic.  Similar to the Helical nebula (Helix Nebula).  Lick photographs show it to have a hint of two intertwining spiral arms.  Appears nearly stellar at low powers but reveals a blurry disk at higher powers.

Celestial Harvest: 300-Plus Showpieces of the Heavens for Telescope Viewing and Contemplation, James Mullaney, Dover Publications

Cat's Eye/Snail Nebula:  Disc with ill-defined edges.  Easily seen in a 3”, striking in 8” and a truly magnificent sight in 14”, showing "Swirling complexity... greenish cast, and a circular void."  The nebula is bright at mag. 8.1 and the central star at mag. 9.5 visually, but the latter is not easy to distinguish in the bright mass of nebulosity.

Celestial Sampler: 60 Small-Scope Tours for Starlit Nights (Stargazing), Sue French, Sky Publishing

At 17X it appears almost stellar, but its’ telltale robin's-egg-blue color gives it away.  The nebula's central star can be distinguished even at this low power.  At 153X the Cat's Eye looks slightly oval (elongated NNE-SSW and perhaps a little darker in the very center.