Tuesday, October 4, 2011

The Veil Nebula in Cygnus: a famous Supernova Remnant!

The Veil Nebula in Cygnus: a famous Supernova Remnant!
Click on the image to enlarge

Ten thousand years ago, before the dawn of recorded human history, a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star and record the colorful expanding cloud as the Veil Nebula. The supernova remnant lies about 1400 light-years away towards the constellation of Cygnus. This supernova remnant actually spans over four times the angular size of the full Moon. The bright star 52 Cygnus is visible with the unaided eye from a dark location but unrelated to the ancient supernova. The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus. It constitutes the visible portions of the Cygnus Loop (radio source W78, or Sharpless 103), a large but relatively faint supernova remnant. The source supernova exploded some 5000 to 8000 years ago, and the remnants have since expanded to cover an area roughly 3 degrees in diameter (about 6 times the diameter, or 36 times the area, of the full moon). The structure is so large that several NGC numbers were assigned to various arcs of the nebula. There are three main visual components:
- The Western Veil (also known as Caldwell 34), consisting of NGC 6960 (the "Witch's Broom") near the foreground star 52 Cygni;
- The Eastern Veil (also known as Caldwell 33), whose brightest area is NGC 6992, trailing off farther south into NGC 6995 and IC 1340; and
- Pickering's Triangle (or Pickering's Triangular Wisp), brightest at the north central edge of the loop, but visible in photographs continuing toward the central area of the loop.
NGC 6974 and NGC 6979 are luminous knots in a fainter patch of nebulosity on the northern rim between NGC 6992 and Pickering's Triangle. The field of view of this image is 4.2 degrees across.
Credit: Davide De Martin/Digital Sky Survey 2 (DSS2)

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