The Crab Nebula: shreds of a supernova

The Crab Nebula (Messier 1) is the brightest and most studied supernova remnant in the sky. Image: Kfir Simon.

It’s perhaps a surprising but definitely disappointing fact that no person alive has seen the titanic explosion of a star as a supernova in our own Milky Way Galaxy. It’s no exaggeration to say when the next one goes off it will be the astronomical event of the millennium up to that point. However, train a humble pair of 10 x 50 binoculars in the direction of the constellation of Taurus, the Bull, on a dark and moonless night and you should be able to detect a faint cloud of light which, fascinatingly, is the debris of a massive star that blew itself out of existence nearly 1,000 years ago.

Now listed as Messier 1 (NGC 1952) and popularly known as the Crab Nebula owing to its resemblance to the crustacean, a moniker coined by Lord Rosse (William Parsons) as far back as the mid-nineteenth century, it is a supernova remnant (SNR), the finest and brightest example of such an object in the entire sky. Appropriately, it holds the honour of being the first entry in Charles Messier’s famous catalogue; the great Frenchman’s independent rediscovery (English physician John Bevis is credited with its discovery, in 1731) of it in August 1758, while he was searching for Halley’s Comet, providing the catalyst for the creation of his list of comet-masquerading deep-sky objects to assist his all-consuming hunt for the icy visitors from the depths of the Solar System. Also, Messier 1 is the only SNR in the Messier Catalogue.    

The Crab Nebula (Messier 1) can be found in the constellation of Taurus, the Bull.

How to observe it

Messier 1 is certainly one of the most famous entries in the first published version of Messier’s indispensable catalogue, but it has the reputation of being the toughest to observe visually of the first 45 entries. The Crab shines with a magnitude of around +8, this being its brightness integrated across its oval-shaped 6 x 4 arcminute form.

Owing to the Crab being one of the most studied and imaged of all astronomical objects, we are very familiar with its beautiful and colourful web-like structure of chaotic and complex filaments weaved in front of its overall background nebulosity. Bearing this in mind, the view through a small- to moderate-aperture telescope may prove something of a disappointment to amateurs starting out on their observing experiences, as none of the filamentary structure can be seen.

However, remember that you what you do see is remarkable – the remains of a titanic supernova that exploded in 1054, which have been expanding and dissipating ever since! As mentioned above, just a humble pair of 10 x 50 binoculars is sufficient to pick it up, and even an 80mm (~three-inch) telescope will give an impression of the Crab’s being orientated south-east to north-west on the sky. Observers using powers of around 100x report that the brighter parts of the diffuse haze give it an ’S’ shape, an impression that is enhanced through larger telescopes.

If you want to catch a glimpse of some of the complex filamentary web, wait for a good night and try a 200mm (eight-inch) telescope with an O-III or, preferably, UHC filter at the eyepiece. Forget seeing the famous Crab pulsar though, unless you’re peering through say a 400–500mm (16- to 20-inch) ‘scope under a truly dark sky on a pristine night.

At least the Crab is east to find, lying just north-west of the southern horn of the Bull, marked by the magnitude +3 star zeta (ζ) Tauri. At early December, M1 offers a generous observing window from around 8pm to 5am, culminating at about 12.30am at an altitude of around 60°.

Hubble Space Telescope’s zoomed in view of the region around the Crab Pulsar (the rightmost of the two bright stars near the center of this image. Image: NASA and ESA.