Star Constellation Facts: Serpens

Serpens (“the Serpent”) is a faint constellation that is unusual in the sense that it is divided into two parts, with both parts depending on each other, as well as a third constellation, Ophiuchus, for context. Its brightest stellar object, Unukalhai, is a giant orange star of magnitude 2.62, and located 75 light years away from Earth. In terms of its shape, the constellation somewhat resembles Hydra, on which it is loosely based, but with the major difference being that Serpens has a distinct “head”, whereas Hydra has no such discernible head.


Out of the 88 recognized constellations, Serpens ranks at 23rd in terms of size, taking up an area of 637 square degrees of the celestial heavens. The constellation entire can be seen between latitudes +80° and -80°, and from the northern hemisphere is best seen in the summer time, especially at about 9 PM (local time) during the month of July. Although Serpens is taken to be in the northern hemisphere, it is divided by the constellation Ophiuchus, the Serpent Bearer into two distinct sections; Serpens Caput, which represents the head of the serpent in the northern sky, and Serpens Cauda as the tail of the snake, which lies in the southern hemisphere. The constellation can be found wrapped around Ophiuchus, just above the zodiacal constellation of Scorpius, the scorpion.


In classical Greek mythology, there is a story that associates Serpens with a snake held by Asclepius, a physician, healer and one of Zeus’ many sons. The story goes that Asclepius once killed a snake, but then watched as the snake was brought back to life by another snake, merely by placing some unknown herbs on it. The exact nature of the herbs has been lost, but the story nevertheless holds that Asclepius subsequently brought people back to life by placing the same herbs used by the snake on their dead bodies. The constellation is generally taken to represent a huge serpent held by Asclepius, and in classical depictions, Asclepius is shown holding Serpens Caput (the top half of Serpens) in his left hand, and Serpens Cauda (the bottom half of Serpens) in his right hand, thus providing context for both halves of the constellation.

Notable Stars

Even though Serpens does not contain any stars of first magnitude, it has some spectacular stars nevertheless.

Star Constellation Facts: Serpens-Unukalhai (Alpha Serpentis) is located about 75 light years away and with an apparent magnitude of 2.62 is the most luminous star in the whole constellation. It is a binary system in which the primary component is an orange, K2 III-class giant that is roughly 12 times as big as the Sun, and at least 38 times as bright. The companion star is an 11th magnitude star about 58 arc seconds away from the primary star.

– Eta Serpentis is the second most luminous star in the constellation, located in Serpens Cauda, the tail of the snake. A K0 III-IV-class subgiant, it is well on its way to becoming a true giant, and it is currently twice as massive as the Sun, 5.8 times as big, and at least 19 times as bright. It has an apparent visual magnitude of 3.260 as seen from its distance of about 60 light years away.

– Gliese 710 is a K7 Vk-class orange main sequence star, with an apparent visual magnitude of 9.69 located about 64 light years away. The star is approaching the Sun, and in about 1.4 million years, it will be within a light year of the Sun, when it will be as bright as the star Antares is now. This might make a pretty picture, but the close proximity of this star has the potential to dislodge a shower of comets from the Oort cloud, which could have dire consequences for the entire solar system.

– Tau Serpentis is without doubt one of the most impressive star systems known. The system consists of 8 gravitationally bound stars, the primary component of which is a M1III-class red giant that is 54 times as big as the Sun, with an absolute magnitude of -2.1. The distances to the stars in this system vary between 900 light years for Tau Serpentis the furthest star, and 160 light years for Tau-5 Serpentis, the closest star. Other stars is the system include-

Notable Deep Sky Objects

– Messier 5 (M5, NGC 5904); this 6th magnitude cluster is one of the oldest and largest globular clusters associated with the Milky Way. It is estimated to be between 12 and 13 billion years old, which makes the oldest stars in the cluster as old as the Milky Way. Among its estimated 500,000 stars are a number of young, hot blue stars, called blue stragglers, which are thought to have formed through star mergers. The cluster is about 24,500 light years away and 80 light years in diameter, which makes it an easy naked-eye object in good seeing conditions.

– IC 4703 (Pillars of Creation); this dramatic part of the Eagle Nebula (M16) consists of 8 diffuse emission nebulae that surrounds M16 proper, which is actually a cluster of stars. Several stars can be seen forming at the tips of light-year-long pillars of gas and dust, but new research suggests that the pillars might have been destroyed in a supernova explosion that occurred between 8,000 and 9,000 years ago. Confirmation of this should reach Earth in about 1,000 years or so, since we are seeing this part of the nebula as it appeared several thousand years ago.

Red Square Nebula– Red Square Nebula (MWC 922) is actually a square nebula, although it is not yet known how the progenitor star, MWC 922, manages to arrange the bi-polar magnetic lines in a square shape. Investigations into the process of formation are ongoing, but so far, all attempts to model the process have failed.

– Hoag’s Object, a 16th magnitude ring galaxy located about 600 million light years away, together with the few other known examples of this type of structure remains one of the most puzzling types of galaxies ever discovered. Current theories hold that the ring structure is the result of galactic interactions, but this has yet to be proven. The nucleus of this galaxy spans about 17 light years, the outer ring is about 75,000 light years in diameter, and the whole structure is about 121,000 light years in diameter- about 20% bigger than the Milky Way.


As of 2016, there have been discovered 12 stars with 15 planets between them in Serpens. One star, HD 168443, has two planets, one being a gas giant 7.6 times as massive as Jupiter, and another gas giant 17.3 times as massive as Jupiter, which makes this object a brown dwarf star, rather than a regular planet.

Meteor Showers

There are two meteor showers associated with Serpens, the Omega, and Sigma Serpentids, both of which peak between December 15th and December 25th. However, being daytime showers, all but the biggest and brightest fireballs are rendered invisible by bright sunlight.

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