NGC 6543
Messier 20, The Trifid Nebula
Optics:   Ritchey–Chrétien 20" F/8.2 (4166mm FL) Processing:   PixInsight, Photoshop
Camera:   SBIG STXL-11000 with Adaptive Optics Date:   July-August 2020
11 Megapixel (4008 x 2672 16-bit sensor) Location:   Columbus, Texas
Exposure:   LRGB = 260:20:20:20 minutes Imager:   Kent E. Biggs
The Cat’s Eye Nebula, cataloged as NGC 6543, is a planetary nebula located in the direction of the constellation Draco, Latin for the dragon. The name Planetary Nebula came about due to the resemblance of these realativly bright nebula to the orbs of planets, but they have no physical resemblance to planets at all. Instead they are clouds of ionized gas often ejected and energized by red giant stars toward the end of their lives. NGC 6543 is one of the brightest planetary nebulae with some structure seen visually through medium size amateur telescopes. Astronomers find distances to planetary nebulae challenging to calculate due to the extreme variability of their size and brightness.

The Cat’s Eye has been estimated by Hubble to be about 3300 light years away, however, other measurements indicated as far as 5300 light years. The small bright middle area is all that is visible in a telescope eyepiece and is only about 16 arc seconds across as indicated by the central circle in this image when hovering over the image. Notice the enlarged inset showing details of the “Cat’s Eye” as well as concentric shells of excited gas surrounding the central star. An arc second is 1/3600th of a degree. This makes the nebula between 0.25 and 0.4 light years across or about 2 trillion miles. The much fainter outer shell of material, as indicated by the large circle in this image, is about 360 arc seconds (6 arc minutes) across or 5-8 light years in diameter (30-50 trillion miles).

Hubble has also tried to estimate the age of the Cat’s Eye Nebula by measuring its rate of expansion at about 1/100th arc second per year. At this rate, the inner nebula may have formed as recently as 1000 years ago. In addition to the inner and outer shells mentioned, there are two more shell groupings of material. One, is inside the inner shell seen here as a very faint inner ellipse better seen in the close-up image below. Another one is in between the inner and outer shells shown here as a transition between the reddish and blueish regions with concentric shells just visible in the image below. These concentric shells began forming about 15,000 years ago at very regular intervals and stopped when the planetary formed a millennium ago. Initially, the red giant that formed this PN was about 5 solar masses (our sun is 1 solar mass). It has since thrown off about 1 solar mass in the form of the outer, middle, inner, and inner-inner shells. Many deep observations by the Hubble Space Telescope show that structurally the Cat’s Eye is an extremely complex PN. These observations reveal knots, jets, bubbles, and complex arcs, being illuminated by the central hot planetary nebula nucleus. It has also been very well-studied from across many different wavelengths.

Hovering a mouse over the top image identifies two other objects: IC 4677, merely a knot in the outer shell of the planetary nebula, and NGC 6552, a fascinating barred spiral galaxy. Hovering a mouse over the bottom image reveals the previous best processed image of this object, note no data has changed between the two images, only processing techniques including a wonderful tool that removed the CCD vertical banding plainly visible! Stats on NGC 6543 are RA 17h 58m 33s, Dec +66° 37' 59", Mag: 8.8, Size: 16" – 300”, Class 3a+2, Central Star Mag: 11.1.

NGC 6543