November 25 – Asteroid 128 Nemesis

Asteroid 128 Nemesis was discovered on November 25th 1872 by J C Watson.  It’s a C-type asteroid, estimated to be about 188km in diameter, and is one of the slower rotators, with a day of 39 hours.  128 Nemesis is the largest member of the Nemesis (or nemesian) family of asteroids, of which at least 129 have been identified by the Sloan Digital Sky Survey.

Nemesis (Louvre, Paris)

Nemesis (Louvre, Paris)

Nemesis, as the name might have already suggested to you, was the Greek goddess of retribution.  She is generally thought to have been the mother of Helen of Troy and her twin sister Clytemnestra, as well as the more astronomically famous twins Castor and Pollydeuces (Pollux).  Obviously, having two sets of twins, while unusual, was nowhere near bizarre enough for the Greeks, so the story goes that Nemesis, attempting to avoid Zeus (as usual) took the form of a goose.  Zeus then turned into a swan, resulting of course in an egg from which her children are born.

What were those guys on?

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:

Location of NGC40 (Caldwell 2). Image credit:

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 the obvious choice.

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.





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