November 25 – Discovery of the “Bow Tie Nebula” (NGC40)

The planetary nebula NGC 40, also known as the Bow Tie Nebula, was discovered by William Herschell on November 25, 1788, using his 18.7 inch reflector. Formed about 4,500 years ago, it is located some 3,000 to 3,500 light years away in the constellation Cepheus (the king, husband of nearby queen Cassiopeia). The nebula measures about 1 light year across.

Location of NGC40 (Caldwell 2). Image credit: freestarcharts.com
Location of NGC40 (Caldwell 2). Image credit: freestarcharts.com

NGC 40 is also designated C2 (Caldwell 2), one of a list of 109 deep sky objects compiled by the famed amateur astronomer Sir Patrick Alfred Caldwell-Moore. The letter “C” was chosen by necessity, Charles Messier having already selfishly claimed Mr Moore’s more obvious choice, “M”.

The Bow Tie Nebula (NGC 40) imaged by CHANDRA (image credit: NASA)
The Bow Tie Nebula (NGC 40) imaged by CHANDRA (image credit: NASA)

A planetary nebula is the shell formed around a dying star that has thrown off its outer layers at the red giant stage of its evolution. In the image above, from the CHANDRA X-Ray Observatory, the blue areas are gases heated to several million degrees Celsius, with the red areas being at a relatively cool 10,000 degrees. Eventually, when the nebula has faded, all that will be left will be a small, dense white dwarf, possibly no bigger than Earth.

I apologise for choosing an image bearing no resemblance to a bow tie, but then Cepheus bears even less to a king. And if you have ever seen my attempts to tie a bow, you might actually see the similarity.


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