Circinus
What is Circinus?
Constellations· Southern autumn · a narrow triangle beside Alpha Centauri. Lacaille's small tribute to the drawing compass. It forms a thin, narrow triangle right beside the bright star Alpha Centauri.
📍 Visible from where you are right now — computed in your browser
Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Circini | 3.2 |
The 1 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.
Constellation basics
| Season | May–Jun evenings; never visible from London or New York |
|---|---|
| Brightest star | α Circini, mag 3.2 |
| How to find | a thin, elongated triangle just south of Alpha Centauri |
| Area rank | 85th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The 'Hand of God' — an X-ray picture drawn by a pulsar in Circinus
About 17,000 light-years away in the direction of Circinus is a pulsar called PSR B1509-58. A pulsar is a fast-spinning neutron star, the tiny, extremely dense core left when a massive star explodes. This one turns about seven times a second and is young, only around 1,700 years old.
In 2009 the Chandra X-ray telescope photographed the space around it. The picture showed a nebula shaped like an open hand with spread fingers, made by particles the pulsar flings out at nearly the speed of light, and about 150 light-years across. Its fingertips touch a nearby gas cloud that glows red, which earned it the nickname the Hand of God.
It is still not clear whether the nebula is really shaped like a hand or only looks that way from our viewing angle. The NuSTAR telescope, which sees higher-energy X-rays, imaged it in 2014 but could not settle the question. Working out its true three-dimensional shape will need more observations.
The constellation in depth
Circinus is one of the constellations Lacaille named after scientific instruments in the 1750s. It represents the compass used to draw circles and is paired with its neighbour Norma, the set square. It is the fourth-smallest of the 88 constellations, and because it sits right next to brilliant Alpha Centauri, it is easily lost in that star's glare.
The brightest star, Alpha Circini, is magnitude 3.2 and about 54 light-years away. Its surface trembles quickly, every few minutes. Astronomers study these vibrations to look inside the star, much as earthquake waves are used to study the inside of the Earth.
In this direction, hidden behind the Milky Way's dust, lies the Circinus Galaxy. It is a nearby galaxy about 13 million light-years away, with a black hole at its centre that shines as it swallows gas. The dust hides it so well in visible light that it was not discovered until 1977; it shows up far better in infrared light and X-rays.
At declinations of −55° to −70° it cannot be seen from Europe or most of the United States. From the southern hemisphere, look on May and June evenings, when Alpha Centauri and Hadar are high, just south of Alpha Centauri. In the Sky view, set Cape Town on a May evening and a thin triangle appears beside Alpha Centauri.
Frequently asked
- When can I see Circinus?
- Circinus is best seen in May–Jun evenings; never visible from London or New York.
- How do I find Circinus?
- To find Circinus, look for a thin, elongated triangle just south of Alpha Centauri.
- What is the brightest star in Circinus?
- The brightest star in Circinus is Alpha Circini, at magnitude 3.2.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.