This is part of the Cygnus Loop in the Cygnus Constellation, also known as the Veil Nebula, a shock wave produced by a supernova that was first visible on earth about 5000 years ago. The triangle was discovered by Williamina Fleming in 1904 on a photographic plate at the Harvard College Observatory, so it is rightly known as Fleming’s Triangle. I understand it was common for such discoveries to be named after the head of an observatory, so it is commonly known as Pickering’s Trioangle, after the head of the observatory. Nice to see this woman finally getting recognition for her work! The red filaments are from ionized hydrogen while the blue filaments are from ionized oxygen.
The image was constructed from 74 x 300 second exposures with an 8” Meade LX200 ACF telescope, ANTILA ALP-T Dual Narrowband filter. ASI294MC-PRO, ASAIR Plus, ASI174mm-mini for guiding with ASI OAG, CEM40 mount. Processed and combined using APP and PS.