IC 1340
cloud of heated and ionized gas and dust
IC 1340, otherwise known as The Bat Nebula and Caldwell 33, is a beautiful portion of the Cygnus loop supernova remnant that reveals delicate wisps and filaments of nebulosity. Sadly, it is often overlooked because of the notoriety of three other portions of the Cygnus loop, namely the Veil Nebula, The Witch's Broom Nebula, and Pickering's Triangle. IC 1340 is the continuation of the Veil Nebula. The nebula lies approximately 1,500 light-years from Earth.
Even though the nebula has a relatively bright integrated magnitude of 7, it is spread over so large an area that the surface brightness is quite low, so the nebula is notorious among astronomers as being difficult to see.
However, an observer can see the nebula clearly in a telescope using an OIII filter (a filter isolating the wavelength of light from doubly ionized oxygen), as almost all light from this nebula is emitted at this wavelength. An 8-inch (200 mm) telescope equipped with an OIII filter shows the delicate lacework apparent in photographs, and with an OIII filter almost any telescope could conceivably see this nebula. Some argue that it can be seen without any optical aid except an OIII filter held up to the eye.