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Physics & Astronomy Department

Astr110 Photography Projects, Fall 2006

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Cat's Eye (NGC 6543), Shannon Goodwin

Cat's Eye Nebula

Cat's Eye Nebula

Lying about 3000 light-years away in the Draco constellation is the planetary nebula NGC 6543, commonly known as the Cat’s Eye Nebula.  William Herschel who classified it as a planetary nebula for its roundish appearance discovered it in 1786.  However, planetary nebulas have nothing to do with planets.  They are formed when a dying star expands and ejects its outer layers of gases leaving behind a core that will collapse and eventually form a white dwarf star.  As the gases are ejected and the core exposed, the core increases in temperature.  At the higher temperatures UV radiation emitted by the core causes the ejected gasses to glow.  In the above images the central core is bright blue.  Based upon blackbody laws this indicates the core to be a high surface temperature as expected for planetary nebulas.  The ejected gases glow bright green indicating they contain the element oxygen.  Other images taken of the Cat’s Eye Nebula from the Hubble Space Telescope show the ejected gases also contain hydrogen and nitrogen.

The Cat’s Eye Nebula with a linear diameter of approximately 9.8 x 10E16 kpc is not as round as other planetary nebula generally are.   In the above images tails can be seen spiraling out from the top and bottom of the image.  The exact reason for these has not been determined.  There could have been multiple pulses or ejections over time occurring in different directions.  It has also been suggested that the central star is actually part of a binary star system, which would alter the shape and direction of ejected material.  Much fainter concentric rings can also be seen expanding beyond the main nebula in the second image.  The gases in these rings are thought to have been ejected much earlier in the star’s history.  Finally, a faint globule of green gas can also be seen to the right of the nebula in the second image.  I could not determine if this gas is connected to the Cat’s Eye Nebula, but the close proximity suggests that it may be left over from a much earlier explosion.  The green color indicates the gas to be composed of oxygen. If you click on the second image an unrelated spiral galaxy can also be seen off to the left that appears close to the Cat's Eye Nebula but is actually light-years away.

References:
Fix, J. D. (2006). Planetary Nebulae. In Astronomy: Journey to the cosmic frontier (4th ed., pp. 457-459). New York, NY: McGraw Hill. (Original work published 1995)

Cat's Eye Nebula. (2006, November 2). Wikipedia. Retrieved November 15, 2006, from http://en.wikipedia.org/wiki/Cat%27s_Eye_Nebula

Hubble probes the complex history of a dying star. (1995, January 11).  HubbleSite. Retrieved November 15, 2006, from http://hubblesite.org/newscenter/archive/releases/1995/01/image/a

 

Right Ascension (J2000) 17:58:30
Declination (J2000) +66:38:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 10x15 seconds in C, 5x60 seconds in B, 10x30 seconds in VR
Date observed

October 12, 2006