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In the image above, north is to the right and east is up.
Pickering's Triangle is part of the northwestern section of the Veil Nebula, a large supernova remnant 1,400 to 2,600 light years distant in the constellation of Cygnus. Surprisingly, even though it is the brightest section of the Veil after the Eastern Veil and Western Veil, it is not in the NGC or IC catalogues. NGC 6979 and NGC 6974 are nearby smaller patches of emission nebulosity to the east. The filamentary segments represent an expanding shell or shock front of the supernova explosion which occured between 5,000 and 8,000 years ago.
As visual observers can attest to with the use of [OIII] filters, the Pickering’s Triangle is strongly enriched in [OIII], as is the whole Veil Nebula.
Pickering's Triangle, in narrow-band filters, natural colors, which this image is part of.