The Crescent nebula in Cygnus. The star at the centre is a Wolf-Rayet (Type WN I think), very massive, and very hot that's blasting out a huge stellar wind that's slamming into the atmosphere that it expelled when it was a red giant. This star is on its last legs and will go bang in the (Astronomical) near future. Imaged in just hydrogen and oxygen, 2 hours each taken in 10 min sub-exposures through my 130 mm f/7 Triplet apo with flattener, focal length 910mm. Red is 100% H, Green is 70% H / 30% O, Blue is 100% O. The orange-red-brown clouds to the bottom right are some of the hydrogen emission nebulae that it's embedded in. The whole of the centre of Cygnus is filled with these hydrogen emission nebulae.