Update 06/01/2023 - This image was named the Webb Deep-Sky Society's Nebula of the
Month for June 2023! See
Webb Deep-Sky Society Nebula of the Month (June 2023)
for more details. You may also visit their home page at
webbdeepsky.com
for more information incuding many great images of the month,
society membership, purpose and activities.
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.