Serpens
What is Serpens?
Constellations· Summer evenings (N) · the only constellation split in two. The only constellation split into two pieces: Ophiuchus grips the snake, so its Head (west) and Tail (east) sit on either side of him. The Tail holds the Eagle Nebula M16 of "Pillars of Creation" fame. Look left and right of Ophiuchus in the Sky view.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Serpens is in your sky right now: https://nowsky.org/solar/sky?sel=con:Serpens — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Unukalhai | 2.6 |
| Alya | 4.6 |
The 2 brightest of the 13 stars used in the figure (11 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | summer evenings (N) |
|---|---|
| Brightest star | Unukalhai (α, 2.6) |
| How to find | either side of Ophiuchus: Head (W) and Tail (E) |
| Area rank | 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Serpens?
- summer evenings (N).
- How do I find Serpens?
- either side of Ophiuchus: Head (W) and Tail (E).
- What is the brightest star in Serpens?
- Unukalhai, magnitude 2.6.
- Where is Serpens in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
A galaxy that is only a ring — Hoag's Object in Serpens
Six hundred million light-years away in the head of Serpens lies an object awkward to call a galaxy. Hoag's Object, found by Arthur Hoag in 1950, is a nucleus of old yellow stars surrounded by a perfect ring of young blue stars with empty space between. Without spiral arms or a disk, only a core and a ring remain, and there is still no settled explanation of how it formed.
The leading idea is that a small galaxy passed straight through and set off a ripple, but no trace of that galaxy is found, and the fact that the stars of the core and the ring rotate the same way is not explained by a simple collision. A famous detail of the Hubble image is a second ring galaxy that happens to show through the gap inside the ring. Serpens is the constellation split in two, and in the sky of its head hides one perfect circle.
The constellation in depth
Serpens is one of Ptolemy's 48 constellations and was originally treated as one figure with Ophiuchus. When the IAU drew formal boundaries in 1930, the snake held in the serpent-bearer's hands became its own constellation — the only one split into two parts, Serpens Caput (the Head) and Serpens Cauda (the Tail). The snake coiled around the staff of Asclepius, god of healing, is its origin.
In the Head, Unukalhai — Arabic for "the serpent's neck" — is a 2.6-magnitude orange giant, and below it M5 is one of the finest globular clusters in the northern sky, resolving into stars in small telescopes. The Tail contains the star-forming Eagle Nebula M16, the site of Hubble's "Pillars of Creation". The deep-red R Serpentis and the double Theta Serpentis are worth a look too.
On June–August evenings find the big pentagon of Ophiuchus in the south; the Head, led by Unukalhai, lies to its west and the Tail sits in the Milky Way to its east. The Head is the easier half. Switch on "More objects" in the Sky view to see where M16 lies.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.