Alpha Centauri

The Alpha Centauri system is the closest star system to our sun. On our sky’s dome, we see this multiple system as a single star – the third-brightest star visible from Earth.

                                

                  Alpha centauri three stars compared to our parent star the SUN

The Alpha Centauri system probably consists of three stars.Alpha Centauri is part of a double, or triple, star system. The two main components are Alpha Centauri A and Alpha Centauri B. The third star, a red dwarf called Proxima Centauri, is thought to be about 4.22 light-years distant and is actually our sun’s closest neighbor among the stars. Is it part of the Alpha Centauri system? The actual status of Proxima as a system member is unclear. It might simply be passing nearby but not part of the system, or it might be gravitationally bound. Still, we say – and others say – that Alpha Centauri is the closest star to our solar system, with the assumption that Proxima is a true part of the Alpha Centauri system.

If you looked through a small telescope at the Alpha Centauri system, you’d see the two main stars, but you wouldn’t see Proxima Centauri. It’s too faint and appears too far (4 diameters of the full moon) away to be easily recognized at part of the system.

Taken by itself, Alpha Centauri A is the fourth-brightest star seen from Earth, just slightly outshone by Arcturus. However, the combined light of Alpha Centauri A and B is slightly greater than Arcturus, so in that sense it is the third-brightest. These stars are an average of 4.3 light-years away.

Yellow Alpha Centauri A is the same stellar type as the Sun (G2), although a bit larger. It looks bright in our sky because of its nearness to Earth. Just a few degrees away, the star Hadar (a separate star sometimes called Beta Centauri, not to be confused with Alpha Centauri B) appears dimmer in our sky than Alpha Centauri. But in fact, Hadar is much farther away at 525 light-years. So you see that Alpha Centauri is not a fabulously brilliant star, as stars go.

Alpha Centauri’s surface temperature is a few degrees Kelvin less than our sun (that is, about 5770 k), but its greater diameter (about 25% more than the sun) and the overall larger surface area gives it a luminosity nearly 1.6 times that of our star.

The smaller member of the system – orangish Alpha Centauri B – is slightly smaller than our sun, with a spectral type of K2. With lower temperature (about 5,300 K) and only half the luminosity of the sun, B would shine as the 21st brightest star in all the heavens by itself.

These two brighter components of the system orbit a common center of gravity once every 80 years. The orbit is notably elliptical, with average distance between the two stars of about 11 A.U., with one A.U. being one Earth-sun distance.

Proxima is the closest star to Earth. Faint red Proxima Centauri – at only 3,100 K and 500 times less bright than our sun – is nearly a fifth of a light year from Alpha Centauri A and B. This great distance is what calls into question its status as part of a triple star system.

Proxima Centauri is a pipsqueak of a star. It’s red dwarf star with only about an eighth of the mass of the sun. If Proxima replace the sun in our solar system, it would shine only as brightly as 45 full moons.

Proxima is a flare star subject to sudden changes in brightness. But its flares are really feeble. On a brighter star, they might not have been noticed.

Proxima’s orbit around the two primary stars in the Alpha Centauri system is thought to take as long as half a billion years.

It’s the closest star to our Earth and sun, about a trillion kilometers closer than the other two star in the Alpha Centauri system. Hence its name.

you can identify the alpha centauri using the southern cross

History and mythology of Alpha Centauri. The Alpha Centauri system appears to the eye as a single bright star, the brightest star in the southern constellation Centaurus the Centaur. Two alternative names for this star, Toliman and Bungula, are rarely used any more. The derivations are somewhat questionable, but Toliman may be from the Arabic forostriches and Bungula apparently derives from Latin meaning hoof.

Thousands of years ago, a motion of Earth called precession – which causes the identity of the Pole Star to change over time – caused Alpha Centauri to appear higher in the sky as seen from the Northern Hemisphere than it does now. But it was still far to the south and often difficult to see.

Classical myth-makers didn’t spend much time with this constellation, although it was thought to represent an uncharacteristically wise centaur that figured in the mythology of Heracles and Jason. The centaur was accidentally wounded by Heracles, and placed into the sky after death by Zeus.

Alpha Centauri itself marked the right front hoof of the Centaur, although little is known of its mythological significance, if any. Ancient Egyptians revered it, and may have built temples aligned to its rising point. In southern China it was part of a star group known as the South Gate.

Astronomers determined the distance to the Alpha Centauri system for the first time in 1839, only a few months after they made the first-ever distance determination to a star (61 Cygni).

Bottom line: The Alpha Centauri system is the closest star system to our sun. On our sky’s dome, we see this multiple system as a single star – the third-brightest star visible from earth