Centaurus
What is Centaurus?
Constellations· Southern autumn–winter · the two Pointers to the Southern Cross. The centaur, half human and half horse. It holds Alpha Centauri, home of the nearest star to the Sun, and the brilliant globular cluster Omega Centauri. From New York its southern half stays below the horizon, and from London only its northern edge scrapes the horizon.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Centauri | -0.3 |
| Hadar | 0.6 |
| Menkent | 2.1 |
| Eta Centauri | 2.3 |
| Zeta Centauri | 2.5 |
| Delta Centauri | 2.6 |
| Iota Centauri | 2.8 |
| Lambda Centauri | 3.1 |
The 8 brightest of the 11 stars used in the figure (10 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | April–July from the south; from New York only its northern half rises above the southern horizon |
|---|---|
| Brightest star | Alpha Centauri (−0.3, third-brightest star) |
| How to find | the two bright Pointers east of Crux |
| Area rank | 9th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Proxima b — a planet at the nearest star
In August 2016 a planet was found circling Proxima Centauri, the nearest star to the Sun. Named Proxima b, it has at least about 1.1 times Earth's mass and goes around its star every 11.2 days. As a planet orbits, it tugs its star back and forth a little, and astronomers found Proxima b by measuring that wobble. The star moves at just 1.4 metres per second, about walking pace.
Proxima b orbits very close to its star. But Proxima is a dim, cool red dwarf, so at that distance the temperature could allow liquid water. Proxima often throws out powerful flares, however, and whether the planet can hold on to an atmosphere has not been confirmed.
At 4.2 light-years, the trip would take tens of thousands of years with today's rockets. Even so, a planet at the nearest star has given plans for interstellar probes a real target. Proxima shines at 11th magnitude, too faint for the naked eye, yet it is the star that first showed us a planetary system next door.
The constellation in depth
Centaurus is Chiron, the wise centaur. Wounded by one of Heracles' poisoned arrows and facing endless pain, he gave up his immortality, and Zeus placed him among the stars. The Southern Cross lies at his feet. It was once part of the centaur and was separated as its own constellation in the late 16th and early 17th centuries.
Alpha Centauri is a group of three stars 4.37 light-years away. One of them, the small red star Proxima, is the closest star to the Sun; even light takes more than four years to cross the gap. Alpha Centauri and its bright neighbour Hadar are known as the Pointers, because a line through them leads to the Southern Cross.
Omega Centauri, with about ten million stars, is the largest globular cluster in our galaxy. To the naked eye it looks like a fuzzy star. Centaurus A is a galaxy 12 million light-years away. The giant black hole at its centre swallows surrounding matter and blasts out jets of gas that shine brightly in radio waves and X-rays.
On southern autumn evenings in April and May, two bright stars stand side by side in the southern sky: Alpha Centauri and Hadar, with the Southern Cross just to the west. From mid-northern latitudes such as New York (40.7° N), Alpha Centauri never rises. The northern half of the figure appears low in the south on spring nights, and Omega Centauri barely clears the horizon. Switch the Sky view's location to Sydney to see the whole centaur.
Frequently asked
- When can I see Centaurus?
- Centaurus is best seen in April–July from the south; from New York only its northern half rises above the southern horizon.
- How do I find Centaurus?
- To find Centaurus, look for the two bright Pointers east of Crux.
- What is the brightest star in Centaurus?
- The brightest star in Centaurus is Alpha Centauri, at magnitude -0.3.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.