Alpha Centauri



=                Alpha Centauri = Alpha Centauri  ( α Centauri, α Cen; also known as   Rigel Kent  /ˈraɪdʒəl ˈkɛnt/ —see   Names) is the brightest   star<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">in the southern <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  constellation<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">of <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Centaurus<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">and is currently inside the <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  G-cloud<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">. <sup class="reference" id="cite_ref-10" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[10] <sup class="reference" id="cite_ref-11" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[11] <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">Although it appears to the unaided eye as a single object, Alpha Centauri is actually a <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  binary star<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  system<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">(designated Alpha Centauri AB<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">or <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  α Cen AB<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">) whose combined <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  visual magnitude<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">of −0.27 makes it the <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  third-brightest<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">star in the night sky after the −1.46 magnitude <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Sirius<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">and the −0.72 magnitude <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Canopus<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">.

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Its individual component stars are named Alpha Centauri A (α Cen A), with 110% of the mass and 151.9% the luminosity of the Sun, and Alpha Centauri B (α Cen B), at 90.7% of the Sun's mass and 44.5% of its luminosity. During the pair's 79.91-year orbit about a common center, the distance between them varies from about that between Pluto and the Sun to that between Saturn and the Sun. They are 1.34 parsecs or 4.37 light years from the Sun.<sup class="reference" id="cite_ref-S_12-0" style="line-height:1em;">[12]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">A third star, known as Proxima Centauri, Proxima or Alpha Centauri C (α Cen C), is probably gravitationally associated with Alpha Centauri AB. Proxima is at the slightly smaller distance of 1.29 parsecs or 4.21 light years from the Sun, making it the closest star to the Sun, even though it is not visible to the naked eye. The separation of Proxima from Alpha Centauri AB is about 0.06 parsecs, 0.2 light years or 13,000 astronomical units (AU); equivalent to 400 times the size of Neptune's orbit.

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">The system may also contain at least one planet, the Earth-sized Alpha Centauri Bb, which if confirmed will be the closest known exoplanet to Earth. The planet has a mass at least 113% of Earth's<sup class="reference" id="cite_ref-Wall_13-0" style="line-height:1em;">[13]  and orbits Alpha Centauri B with a period of 3.236 days.<sup class="reference" id="cite_ref-Dumusque_14-0" style="line-height:1em;">[14]  Orbiting at a distance of 6 million kilometers from the star,<sup class="reference" id="cite_ref-Wall_13-1" style="line-height:1em;">[13]  4% of the distance of the Earth to the Sun and a tenth of the distance between Mercury and the sun, the planet has an estimated surface temperature of 1500 K (roughly 1200 °C), too hot to be habitable