Sh2-240 - wonderfuluniverse.de

Sh2-240 from my backyard

In 2016, together with my astrophotography companions Ralf Kreuels, Mark Schocke, and Michael Kunze, I embarked on an ambitious project to image the vast Spaghetti Nebula (Sh2-240), one of the largest known supernova remnants in the sky. Owing to its enormous angular size of nearly three degrees, the nebula was ideally suited for wide-field imaging with 200 mm telephoto lenses. We acquired extensive RGB data alongside narrowband Hα and OIII exposures, allowing us to reveal both the delicate filamentary hydrogen structures and the faint oxygen emission that traces the expanding shock front of the ancient supernova remnant.

The individual datasets were meticulously calibrated, registered, and combined into a single high-resolution composite that captured the remarkable complexity of this elusive object. The finished image was honored with publication in the Astronomy Photographer of the Year Book 2016, accompanying the prestigious competition organized by the Royal Observatory Greenwich. This recognition was a rewarding culmination of a truly collaborative effort and remains one of the highlights of our astrophotography work.

Sh2-240 is the Sharpless catalog name for the Spaghetti Nebula, also known as Simeis 147 or S147. It is a large, faint supernova remnant on the border of Taurus and Auriga, famous for its long, filamentary structure that really does look like tangled strands.

Unlike an emission nebula powered by young stars, Sh2-240 is the leftover shell of a supernova explosion. The blast happened long ago, and the expanding shock wave is still heating and ionizing the surrounding gas, which makes the nebula glow in narrowband images. This is why the object is scientifically interesting: it shows the later life of a massive star after the explosive end of its evolution.

The nebula is huge on the sky, covering about 3 degrees, which is around six full Moons across. At an estimated distance of roughly 3,000 to 4,500 light-years, that apparent size translates into an actual diameter of roughly 140 to 220 light-years, depending on which distance estimate is used. That makes it one of the larger and older supernova remnants still showing a recognizable structure in the Milky Way.

Most sources place its age at about 40,000 years. It was first discovered in 1952 at the Crimean Astrophysical Observatory by Grigori Shajn using a Schmidt camera and H-alpha filters. Later work identified it as a supernova remnant rather than an ordinary emission nebula, and studies have also found a pulsar in its interior, consistent with a collapsed stellar core left behind by the explosion.

Sh2-240 is one of those targets that astrophotographers love and casual observers often miss, because it is extremely faint. Its structure is made of thin loops and arcs, with glowing hydrogen and oxygen emission tracing the shock fronts where the remnant is plowing into interstellar gas. In images, the fine filaments give it a delicate, web-like appearance rather than a bright, compact shape.

Astronomers study Sh2-240 because it is a good laboratory for supernova remnant evolution, shock physics, and the interaction between ejecta and the interstellar medium. The remnant is old enough that its expansion has slowed and its structure has become intricate, but it is still young enough to preserve clear evidence of the original explosion. That balance makes it especially useful for comparing with better-known remnants like the Veil Nebula.

For the DSW data the calibration, registration and the final processing was done with PixInsight. The result was as follows: