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Designations:
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NGC 6992 & NGC 6995, Caldwell (C33), Veil Nebula (Eastern Segment)
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Object Type:
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Constellation:
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Cygnus
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20 hr 56 min 24 sec (2000.0)
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+31° 43 min (2000.0)
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7.5
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Size:
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60 X 8 arcminutes
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Distance:
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2500 light years
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Discoverer:
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William Herschel, 1784
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About 15,000 years ago an unknown star died spectacularly in Cygnus.
The event, a Type II supernova explosion, would have briefly dominated the night sky on Earth. If
prehistoric peoples were in the habit of gazing toward the heavens for meaning, they might have found
it in the sudden appearance of this "new" star, which could have rivaled the full Moon in brilliance
and remained visible for weeks in broad daylight. The creators of the oldest known human art, the
Cro-Magnon, might have witnessed this stellar apparition, and conceivably they recorded the event
in a cave painting somewhere - though if they did, the artwork remains undiscovered. What has been
discovered is the remnant of that powerful blast. Popularly known and the Veil Nebula, NGC 6960,
NGC 6992 and NGC 6995 together constitute the corpse of a single supergiant star that perished in a
supernova explosion. (More than 100 such corpses are known; doubtless many others await discovery.)
Also known collectively as the Cygnus Loop, the entire wreathlike complex is an illusion of sorts.
Its various pieces are parts of an expanding shell of dimly glowing gas measuring six Moon diameters
in our sky, or 80 light-years in space; it appears looplike in part because we see more gas in a give
square
arcminute
of sky when we look at the shell's edges that when we gaze through its middle. A
photograph of the Veil seems to tell a simple yet haunting tale, one that has been echoed over and
over again since time immemorial - that life, even for things cosmological ends in death.
A Type II supernova announces the death of a supergiant star - one that starts life with at least 8 times the mass of the Sun. Betelgeuse, in Orion's shoulder, is a supergiant, as is Antares at the heart of Scorpius. Such stars age about 1,000 times faster than does our Sun. As it ages a supergiant star forges ever-heavier atomic nuclei, from carbon early in its life to iron near the end. Each nuclear-fusion stage releases energy and helps the star fight the ever-present pull of gravity. Once the star's core creates iron, however, nuclear fusion can proceed there no further. (Energy is consumed, rather than generated, by the fusion of elements heavier than iron.) Since energy is no longer being released, the outward pressure that supported the star stops. The star succumbs to the force of gravity. Within seconds the core of the once-mighty supergiant collapses into a sphere mearly 10km across. The rest of the star rushes inward, only to rebound off that dense core. A quarter-second later, the star ends its life in a cataclysmic explosion that will shine with the light of a billion Suns - the luminosity of a small galaxy. The blast hurls several solar masses of material outward at speeds measured in thousands of km per second. Plowing through space, the ejecta collide with interstellar material, heating it up and causing it to glow. The ejecta will continue to expand into space until it fully dissipates and becomes part of the interstellar medium. Sprinkled among the fleeing debris are the newly forged atoms of heavy elements like gold, silver and calcium. Many of the keepsakes we treasure - a wedding band; a great-grandmother's silver pendant; an Olympian's medal; a child's tooth - are made of atoms dispersed by supernova explosions before our solar system was born. |
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Telescope:
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Focal Length:
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480 mm with .8x Televue reducer / flattener (384mm effective focal length)
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Mount:
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Camera
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Guider:
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Exposures:
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8 7-minute Luminance exposures, 5 7-minute exposures for each color (RGB) for a total of 161 minutes.
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Location:
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Cicero, IN
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Software:
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CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
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