Serpens - The Serpent

Serpens is an ancient constellation, which was later divided into two parts. Serpens Caput (the head) lies on the east side of Ophiuchus, and Serpens Cauda (the tail) is on the west side. Serpens is a large constellation with few prominent stars. It is best seen from June to September.

History and Mythology

This constellation dates from Ptolemy's star catalog of the 2nd century AD. Serpens signifies the serpent with which Ophiuchus struggled. The snake is a symbol of poison, which can both kill and cure. The snake's shedding of its skin also signifies rebirth.

Notable Stars

In the "Caput" (head) portion of the constellation, the brightest star is Unukalhai (whose name means "serpent's neck") of magnitude 2.7, and at a distance of 75 light-years. It is a class K star with a lower surface temperature than our Sun.

Serpens Cauda, the tail portion, contains the double star Alya, with components of magnitude 4.1 and 5.0, separated by 22".

Clusters, Nebulae, and Galaxies

M 5 is regarded as one of the finest globular clusters in the northern sky. It appears in Serpens Caput. It is of 6th magnitude and can be seen with binoculars. IC 4756 is a scattered star cluster of 5th magnitude in the northernmost part of Serpens Cauda.

Serpens Cauda includes the splendid star cluster and nebula M 16. This is known as the Eagle Nebula. It is a 6th magnitude star cluster enveloped by a nebula. In an 8 inch telescope at low power, M 16 is an impressive object.

M 16 is filled with dark regions and globules, including a peculiar dark column and a luminous rim around the cluster. These objects were the subject of the famous "Pillars of Creation" image taken by the Hubble Space Telescope.

A challenging object for larger telescopes is Seyfert's Sextet, a very compact cluster of six galaxies superimposed upon one another in Serpens Caput. It includes NGC 6027, 6027A, 6027B, 6027C, 6027D, and 6027E. This group of galaxies is about 190 million light years away.