Cygnus Loop
 Cygnus Loop compared to the Moon
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The Cygnus Loop (radio source W78, or Sharpless 103) is a large supernova remnant (SNR) in the constellation Cygnus, an emission nebula measuring nearly 3° across. Some arcs of the loop, known collectively as the Veil Nebula or Cirrus Nebula, emit in the visible electromagnetic range. Radio, infrared, and X-ray images reveal the complete loop.
The visual portion of the Cygnus Loop is known as the Veil Nebula, also called the Cirrus Nebula or the Filamentary Nebula. Several components have separate names and identifiers, including the "Western Veil" or "Witch's Broom", the "Eastern Veil", and Pickering's Triangle.
NGC 6960, the Western Veil, is the western part of the remnant, also known as the "Witch's Broom", located at J2000 RA 20h 45m 58.1sDec +30° 35′ 43″. As the western-most NGC object in the nebula (first in right ascension), its number is sometimes used as an NGC identifier for the nebula as a whole.
These three luminous areas make up the Eastern Veil. NGC 6992 is an HI shell located along the north-eastern edge of the loop at J2000 RA 20h 56m 19.0sDec +31° 44′ 34″. NGC 6995 is located farther south at J2000 RA 20h 57m 10.7sDec +31° 14′ 07″, and IC 1340 even farther south at J2000 RA 20h 56m 12.0sDec +31° 04′ 00″.
Also known as Pickering's Wedge, or Pickering's Triangular Wisp, this segment of relatively faint nebulosity was discovered photographically in 1904 by Williamina Fleming at Harvard Observatory, where Edward Charles Pickering was director at the time. The Triangle is brightest along the northern side of the loop, though photographs show the nebulosity extending into the central area as well.
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