Serpens, or the Snake, is a constellation in the northern hemisphere. It was introduced by the Greek astronomer Ptolemy in the 2nd century. Serpens is the only constellation that is divided into two sections, Serpens Caput ("the serpent's head") and Serpens Cauda ("the serpent's tail"). The constellation Ophiuchus
, the Snake Holder, lies between the two. Serpens and Ophiuchus
used to be a single constellation.
In Greek mythology, Ophiuchus
represents the healer Asclepius, who once killed a snake and then observed another snake bring it back to life using healing herbs. It is said that this was how Asclepius learned the secrets of medicine and to bringing people back from the dead, which is why the serpent was placed in the sky.
The constellation Serpens occupies an area of 637 square degrees and contains five stars with known planets. It can be seen at latitudes between +80° and -80° and is best visible at 9 p.m. during the month of July.
alpha Serpentis is the only star in the constellation brighter than third magnitude. It is a multiple star also known as Unukalhai ("the neck of the snake") and Cor Serpentis ("the heart of the snake"). Unukalhai is part of Serpens Caput and lies 73.2 light-years from Earth. The primary component is an orange giant with luminosity 70 times that of the Sun.
eta Serpentis, the second brightest star, is an orange giant that has a magnitude 12 companion. The binary star is 61.8 light-years distant. It is also known by its traditional Chinese name, Tang, after the Tang dynasty.
mu Serpentis or Leiolepis ("smooth scaled") is the third brightest star. It is a white dwarf that lies about 156 light-years from Earth.
xi Serpentis is another multiple star, about 105 light-years distant. It is also known as Nehushtan, a name that refers to Moses’ bronze serpent. The primary component is a yellow giant, a spectroscopic binary, and it has a faint, magnitude 13 companion.
beta Serpentis, another multiple star system, consists of a white dwarf and two companion stars. It is approximately 153 light-years distant. Beta Serpentis belongs to the Ursa Major Moving Group of stars.
delta Serpentis also consist of two binary stars and lies about 210 light-years from Earth. It is sometimes known as Chin, after the Chin dynasty. The primary component is a yellow-white subgiant classified as a Delta Scuti variable star, while the fainter companion is also an F class subgiant. The second pair consists of magnitude 14 and magnitude 15 stars.
gamma Serpentis, a yellow-white dwarf, is about 36.3 light-years distant and also known by the name Ainalhai ("the eye of the serpent"). The star has two optical companions.
epsilon Serpentis, or Nulla Pambu ("the good snake") is another white dwarf, about 70.3 light-years distant.
theta Serpentis, also known as Alya ("sheep’s tail"), marks the tip of the serpent’s tail. It is a multiple star system, 132 light-years distant. The two main components are both white dwarfs, while the third component is a yellow G-type star.
kappa Serpentis is a red giant, 348 light-years distant. It has a magnitude of 4.09.
Serpens also contains several notable deep sky objects. Messier 16 (NGC 6611), also known as the Eagle Nebula, is in fact a young open star cluster whose shape resembles that of an eagle. The cluster contains an area known as the "Pillars of Creation,” a large star forming region with a structure similar to that of the “Mountains of Creation” in the constellation Cassiopeia
. The Pillars are believed to have been destroyed in a supernova explosion some 6,000 years ago, but their new appearance will not be seen on Earth for another thousand years. The Eagle Nebula is part of a diffuse emission nebula, IC 4703, which is an active star forming region, approximately 6,500 light-years distant.
Messier 5 (NGC 5904) is a globular cluster about 165 light-years in diameter, that appears as a faint star to the naked eye. The brightest stars in the cluster are of magnitude 12.2. Messier 5 is one of the largest globular clusters ever discovered. It contains over 100 variable stars. It is one of the older clusters in the Milky Way, believed to be about 13 billion years old.
The Serpens South star cluster is a densely populated area that contains about 50 young stars, 35 of which are only beginning to form. The cluster lies 848 light-years from Earth.
The Red Square Nebula, or MWC 922, is a symmetric bipolar nebula that contains a number of hot stars, notable for having the shape of a perfect square. It lies close to Messier 16.
Serpens belongs to the Hercules family of constellations, along with Hercules
, Corona Australis
, Triangulum Australe
Constellations directly bordering Serpens are Corona Borealis