Your guide to astrophotography

NGC 6888 – The Crescent Nebula is an emission nebula located about 5,000 light-years away in the constellation Cygnus. While its name suggests a crescent shape, its true form is more complex, appearing as a delicate, semi-circular shell of ionized gas and dust. This nebula marks the remnants of a massive Wolf-Rayet star, HD 192163, which is at the center of the structure. The star’s powerful stellar winds have sculpted the nebula into the shape we observe today, pushing gas outward and creating intricate layers of glowing gas.

The Crescent Nebula is a classic example of a Wolf-Rayet nebula, a region where a massive star is shedding its outer layers, creating dramatic interactions with surrounding material. As the star expels its high-energy radiation, it ionizes the surrounding gas, making it glow in rich hues of red, blue, and green.

For astrophotographers, NGC 6888 offers a stunning display with its structure and dynamic processes making it a captivating object of study and observation. The nebula shines brightly in hydrogen-alpha (Hα) emission lines, which makes it an excellent target for narrowband filters (especially in the Hα, OIII, and SII wavelengths). In long-exposure astrophotography, even relatively small telescopes can capture striking details with the right equipment. The nebula’s intricate gas structures and colorful emission lines (due to ionized hydrogen and oxygen) can be captured with even modest setups, as long as there is adequate exposure time.

SH2-91, located in the constellation Cygnus, is a fascinating supernova remnant lying about 6,000 light-years from Earth. This celestial object is the aftermath of a massive stellar explosion, where the outer layers of a dying star were ejected into space, creating a cloud of ionized gas and debris. The remnant is part of the Sharpless catalog of H II regions, though its nature as a supernova remnant distinguishes it from the more commonly known emission nebulae in this catalog.

SH2-91 is sometimes referred to as “The Other Veil in Cygnus”, because a much brighter and popular supernova remnant called the Veil Nebula also resides in Cygnus.

This particular image is a 5-panel mosaic and only captures a small portion of the entire faint structure. The supernova that created SH2-91 is thought to have occurred several thousand years ago, and the remnant’s structure is shaped by the shockwaves from the explosion. These shockwaves interact with surrounding gas and dust, creating a complex, expanding shell of material. SH2-91 is relatively faint and not immediately visible to the naked eye, but it can be detected in deeper observations, where it appears as a faint, diffuse glow.