Explanation: The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of the nebula in this impressive wide-angle view. But this wide and deep image combining data from two telescopes also reveals its extremely faint outer halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the right, some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552.
https://en.wikipedia.org/wiki/Cat's_Eye_Nebula wrote: The Cat's Eye Nebula is a convenient and accurate marker for the axis of rotation of the Earth's ecliptic, around which the celestial North Pole rotates. It is also a good marker for the nearby "invariable" axis of the solar system, which is the center of the circles which every planet's north pole, and the north pole of every planet's orbit, make in the sky.
Does this mean that the Cat's Eye is on the North Ecliptic pole of all of the planets? Or does it mean something else?
https://en.wikipedia.org/wiki/Cat's_Eye_Nebula wrote: The Cat's Eye Nebula is a convenient and accurate marker for the axis of rotation of the Earth's ecliptic, around which the celestial North Pole rotates. It is also a good marker for the nearby "invariable" axis of the solar system, which is the center of the circles which every planet's north pole, and the north pole of every planet's orbit, make in the sky.
Does this mean that the Cat's Eye is on the North Ecliptic pole of all of the planets? Or does it mean something else?
The ecliptic poles are defined by the plane of the Earth's orbit around the Sun, which no other planet lies on. Every planet has its own ecliptic poles just like it has its own celestial poles.
Chris
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Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
The structure of the Cat's Eye Nebula is very intricate: The twirls, curls, shocks, nested spheres, inner spirals and jets are all consequences of mass loss. The question is how these structures have come about.
To me there appear to be similarities between central stars of planetary nebulas and Wolf-Rayet stars:
The edge of nebula M1-67 surrounding Wolf-Rayet star WR 124 is also tattered and broken, although less so than the outer edge of the halo surrounding the Cat's Eye Nebula. To me, the outer boundary of the halo of the Cat's Eye Nebula suggests a violent mass loss event. But the nested shells inside the halo suggest something else to me - maybe something similar to Wolf-Rayet star WR 140?
The star is what is known as a colliding wind binary, consisting of an extremely rare Wolf-Rayet star, called WR 140, and a hot, massive O-type star companion – another rare object.
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Both stars in the WR 140 system have fast stellar winds, blowing out into space at around 3,000 kilometers (1,864 miles) per second. Both are therefore losing mass at a pretty furious rate.
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When the two stars enter periastron – a distance about a third greater than the distance between Earth and the Sun – they become close enough that their powerful winds collide.
This produces shocks in the material around the stars, accelerating particles and generating energetic radiation, such as X-rays. These colliding winds also induce episodes of dust formation as the material in the colliding stellar wind cools.
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Because the binary star's orbit has a 7.94-year period, the wind collision and dust production occur like clockwork every 7.94 years. This means you can count the rings of the nebula around the binary, like tree rings, to determine the age of the outermost visible dust shell.
Click to play embedded YouTube video.
Could the central star of the Cat's Eye nebula be a binary star? I guess that's possible:
It is also suspected that the central WR:+O7 spectral class PNN star, HD 164963 / BD +66 1066 / PPM 20679 of the nebula may be generated by a binary star. The existence of an accretion disk caused by mass transfer between the two components of the system may give rise to polar jets, which would interact with previously ejected material. Over time, the direction of the polar jets would vary due to precession.
Outside the bright inner portion of the nebula, there are a series of concentric rings, thought to have been ejected before the formation of the planetary nebula, while the star was on the asymptotic giant branch of the Hertzsprung–Russell diagram. These rings are very evenly spaced, suggesting that the mechanism responsible for their formation ejected them at very regular intervals and at very similar speeds. The total mass of the rings is about 0.1 solar masses. The pulsations that formed the rings probably started 15,000 years ago and ceased about 1000 years ago, when the formation of the bright central part began (see above).
Further, a large faint halo extends to large distances from the star. The halo again predates the formation of the main nebula. The mass of the halo is estimated as 0.26–0.92 solar masses.
Oh, and - as for my comparison with the central star of the Cat's Eye Nebula and a WR star, Wikipedia said that the central star of the Cat's Eye Nebula has a WR-like spectrum:
Surface temperature for the central PNN is about 80,000 K, being 10,000 times as luminous as the sun. Stellar classification is O7 + [WR]-type star.
Wikipedia wrote: Planetary nebulae distances like NGC 6543 are generally very inaccurate and not well known.[21] Some recent Hubble Space Telescope observations of NGC 6543 taken several years apart determine its distance from the angular expansion rate of 3.457 milliarcseconds per year. Assuming a line of sight expansion velocity of 16.4 km·s−1, this implies that NGC 6543's distance is 1001±269 parsecs (3×1019 k or 3300 light-years) away from Earth.[22] Several other distance references, like what is quoted in SIMBAD in 2014 based on Stanghellini, L., et al. (2008) suggest the distance is 1623 parsecs (5300 light-years).
It seems there are different assumptions on the distance, so the distance mentioned by APOD is not obsolete.
https://en.wikipedia.org/wiki/Cat's_Eye_Nebula wrote: The Cat's Eye Nebula is a convenient and accurate marker for the axis of rotation of the Earth's ecliptic, around which the celestial North Pole rotates. It is also a good marker for the nearby "invariable" axis of the solar system, which is the center of the circles which every planet's north pole, and the north pole of every planet's orbit, make in the sky.
Does this mean that the Cat's Eye is on the North Ecliptic pole of all of the planets? Or does it mean something else?
The ecliptic poles are defined by the plane of the Earth's orbit around the Sun, which no other planet lies on. Every planet has its own ecliptic poles just like it has its own celestial poles.
I got the part that each planet's ecliptic pole, or orbital pole is different from each other, though they all lie in constellation Draco. But I'm still trying to understand what exactly is Invariable plane of the solar system. It says it's the result of angular momentum of all objects in Solar system, whatever that means.
https://en.wikipedia.org/wiki/Cat's_Eye_Nebula wrote: The Cat's Eye Nebula is a convenient and accurate marker for the axis of rotation of the Earth's ecliptic, around which the celestial North Pole rotates. It is also a good marker for the nearby "invariable" axis of the solar system, which is the center of the circles which every planet's north pole, and the north pole of every planet's orbit, make in the sky.
Does this mean that the Cat's Eye is on the North Ecliptic pole of all of the planets? Or does it mean something else?
The ecliptic poles are defined by the plane of the Earth's orbit around the Sun, which no other planet lies on. Every planet has its own ecliptic poles just like it has its own celestial poles.
And of course, the fact that the Cat's Eye Nebula is "a good marker for the Earth's north ecliptic pole" means that it is very close to it: in fact, ten times closer than the more common naked eye visible "marker" Polaris! The sentence just prior to the Wikipedia quote is:
NGC 6543 is 4.4 minutes of arc from the current position of the north ecliptic pole, less than 1⁄10 of the 45 arcminutes between Polaris and the current location of the Earth's northern axis of rotation.
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rmroyster@pocatlanta.com wrote: ↑Thu May 25, 2023 11:56 pm
Is that a supernova in the top star trail of NGC6552 in todays picture? 5/25/2023 Marvin Royster
If a prominent star is "suggestively placed" in a galaxy, and you wonder if it is a supernova, then it is a good idea to look for other pictures of the same galaxy and see if the star turns up in those pictures, too.
NGC 6552 in the APOD.
NGC 6552 from Wikipedia.
You can see that the orientation of the pictures is different, but the stars are the same. So we can say with confidence that none of the stars seen in or close to NGC 6552 is a supernova. Instead they are foreground Milky Way stars.
Also, if APOD presents a picture of a galaxy, even a background galaxy, in which a supernova is clearly visible, then I definitely expect the APOD caption to tell us about the supernova.
I wonder what all the ragged petals of the larger (faster? earlier?) outskirts are in 3D.
Can they be grazing-angle reflections of the white dwarf light off dust particles near our line of sight?
Can there be light echoes of several flashes the white dwarf emitted early on?
Can the dust belong to a foreground cloud unrelated to the Cat's Eye?
After all, the ring of those ragged petals is suspiciously round while the Cat's Eye has a complex geometry with a pair of slightly curved jets and some rings, and none are by any means aligned with our line of sight.
If so, those petals would have all in all thermal spectrum modified by reflection: somewhat brownish because of absorption in a dust particle's surface and somewhat bluish because the shorter wavelength photons reflect off the larger fraction of tiny dust particles, using the smaller ones too.
Last edited by VictorBorun on Fri May 26, 2023 7:31 pm, edited 1 time in total.
Is the Cat's Eye in or out of the thick (=thin in density) disk of the Milky Way?
They say that Polaris (α Ursae Minoris) is about 447.6 ly ±0.3 pc away and still in the thick (=low density) disk of the Milky Way, though maybe out of the thin (=thick in density) disk.
Cat's Eye Wide and Deep
