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.





February 15 – The Cat’s Eye Nebula

NGC 6543

Everybody’s seen photographs of this one, but that’s no reason to not show it again: it’s the Cat’s Eye Nebula, otherwise known as NGC 6543, (or “Caldwell 6″ in Patrick Moore’s list of more challenging, non-Messier objects), an expanding cloud of mostly hydrogen and helium, discovered on February 15th 1786 by William Herschel.

Hubble image of the Cat's Eye Nebula (image credit: NASA/ESA)
Hubble image of the Cat’s Eye Nebula (image credit: NASA/ESA)

The nebula is one of the most complex we know of, and was formed around 1,000 years ago when the star (or stars – it may be a binary system) at its centre lost its outer shell. That star, smaller than the Sun but approximately 10,000 times as luminous, is what is responsible for the nebula being lit up like a Christmas tree.

NGC 6543 is around 3,000 light years away and has an observed density of about 5,000 particles per cubic cm.


Launched on February 15th 1973 from the Baikonur Cosmodrome, Prognoz 3‘s purpose was to study solar flares, and help increase our understanding of how the Sun’s activity affects the Earth’s magnetosphere. Prognoz launches took place at an impressive rate. Getting the entire fleet of 10 satellites off the ground only took 54 weeks.


Asteroid 442 Eichsfeldia was discovered on February 15th, 1899, by Max Wolf and Arnold Schwassman. It’s a C-type main belt asteroid of approximately 65 km diameter.