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Reference.org
Cygnus Loop
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<p>The Cygnus Loop (radio source W78, or Sharpless 103) is a large <a href="/facts/Supernova_remnant/tYboe2n4">supernova remnant</a> (SNR) in the <a href="/facts/Constellation/nBQqgW8A">constellation</a> <a href="/facts/Cygnus_(constellation)/L1fYe414">Cygnus</a>, an <a href="/facts/Emission_nebula/UzUTgCp8">emission nebula</a> measuring nearly 3° across. Some arcs of the loop, known collectively as the <a href="/facts/Veil_Nebula/2wFA2Ekn">Veil Nebula</a> or Cirrus Nebula, emit in the visible <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic</a> range. Radio, infrared, and X-ray images reveal the complete loop. </p>