Constellation, Octant
Octans
A navigator’s reflecting octant, chosen by Nicolas Louis de Lacaille for the faint region around the south celestial pole. Fittingly, sailors used the octant to measure the height of the pole.
From New York the constellation Octans never rises above the horizon: it belongs to the other hemisphere’s sky.
From New York the constellation Octans never rises above the horizon: it belongs to the other hemisphere’s sky.
In the 3D sky
The sky over New York turned towards Octans. Drag to look around.
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Evening visibility over the year
Height of the constellation’s centre above the horizon at 10 pm local time on the 15th of each month, from New York. Above about 30° it is well placed.
Name and history
Octans represents the reflecting octant, a navigation instrument invented in 1730 by the Englishman John Hadley. Nicolas Louis de Lacaille called it l’Octans de Reflexion on his chart of 1756 and shortened it to Octans in 1763. He described it as the main instrument navigators used to measure the height of the pole. So he placed it right over the south celestial pole. Its frame is an arc of one eighth of a circle, which gives the octant its name. A later version with a longer arc became the sextant.
To build the figure, Lacaille took over stars that had belonged to Hydrus and Apus, reshaping this part of the sky. The south has no bright pole star like Polaris. The nearest star visible to the eye, Sigma Octantis, is faint and hard to find. Octans is also one of the constellations whose Alpha star is not its brightest. There are no myths attached to it.
Sources: Ian Ridpath, Star Tales: Octans
Brightest stars
| Star | Designation | Magnitude | Distance |
|---|---|---|---|
| ν Oct | ν Oct | 3.73 | 69 light-years |
| β Oct | β Oct | 4.13 | 149 light-years |
| δ Oct | δ Oct | 4.31 | 299 light-years |
| θ Oct | θ Oct | 4.78 | 217 light-years |
Facts
| Area | about 291 square degrees (50 of 88) |
|---|---|
| IAU abbreviation | Oct |
| Sky | Southern sky |
| Origin | First shown as l’Octans de Reflexion on Lacaille’s planisphere of 1756, from his observations at the Cape in 1751–52 |
| Stars brighter than magnitude 5 | 4 |
| Centre (J2000) | 22.2 h, -83° |
Deep-sky objects
Galaxies, clusters and nebulae brighter than magnitude 9, from the OpenNGC catalogue. Most need binoculars or a telescope and a dark sky.
No deep-sky object brighter than magnitude 9.
Boundaries: International Astronomical Union, via Astronomy Engine. Areas are computed from the boundaries by sampling (within about one percent). Names and lines: Stellarium. Stars: HYG Database. Deep-sky objects: OpenNGC. Calculated with Astronomy Engine, an open-source library verified against the US Naval Observatory and NASA JPL. Data sources
How to use this page
Choose your place and a night at the top. The answer and the 3D view show where the constellation is, when it is highest and whether it rises at all from where you are. The chart shows its stars and lines, and the tables list its brightest stars and the deep-sky objects inside it.
Frequently asked questions
When is a constellation best seen?
When it is highest in a dark sky, which the page gives for the night you pick. Each constellation is best placed in a particular season, because the stars rise about four minutes earlier every night.
Why can I not see a constellation from my place?
Constellations far south of the celestial equator never rise from northern places, and those far north never rise from southern ones. The page says when this is the case.
What are the constellation boundaries?
The International Astronomical Union divides the sky into 88 areas with official boundaries. The stick figures are only a drawing aid, the boundaries say which constellation a point in the sky belongs to.
Related guides
- How to learn the constellationsStart with one bright pattern you cannot miss, use it as a signpost to its neighbours, and come back a month later: the sky will have turned, and you will know a little more of it.
- Altitude and azimuth: finding things in the skyTwo angles tell you exactly where to look: which direction, and how high.
- Light pollution and dark skies: the Bortle scaleFrom a city centre you can count a few dozen stars. From a truly dark site you can count a few thousand, with the Milky Way bright enough to cast a shadow. The Bortle scale puts a number on the difference.
- Binoculars for stargazing: what to buy and what to look atA pair of 7x50 or 10x50 binoculars shows the craters of the Moon, the moons of Jupiter, dozens of star clusters and the Andromeda Galaxy, for a fraction of the cost of a telescope.