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Acrux
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<p>Acrux is the brightest <a href="/facts/Star/euBFuo07">star</a> in the southern <a href="/facts/Constellation/nBQqgW8A">constellation</a> of <a href="/facts/Crux/Btht6rAc">Crux</a>. It has the <a href="/facts/Bayer_designation/KU2DVT47">Bayer designation</a> α Crucis, which is <a href="/facts/Latinisation_of_names/69CA5FuQ">Latinised</a> to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined <a href="/facts/Visual_magnitude/7pCTF1Me">visual magnitude</a> of +0.76, it is the <a href="/facts/List_of_brightest_stars/0vDnLEYM">13th-brightest star</a> in the <a href="/facts/Night_sky/IM1PakDh">night sky</a>. It is the most southerly star of the <a href="/facts/Asterism_(astronomy)/CFu0Qllg">asterism</a> known as the Southern Cross and is the southernmost <a href="/facts/First-magnitude_star/how71YFQ">first-magnitude star</a>, 2.3 degrees more southerly than <a href="/facts/Alpha_Centauri/6BlySfIj">Alpha Centauri</a>. This system is located at a distance of 321 <a href="/facts/Light-year/IGc5NdQb">light-years</a> from the <a href="/facts/Sun/CadPCVHh">Sun</a>. </p><p>To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical <a href="/facts/Telescope/BDwYahhR">telescopes</a>, Acrux appears as a <a href="/facts/Triple_star_system/1vX99BMV">triple star</a>, whose two brightest components are visually separated by about 4 <a href="/facts/Arcsecond/tybs6YGC">arcseconds</a> and are known as Acrux A and Acrux B, α1 Crucis and α2 Crucis, or α Crucis A and α Crucis B. Both components are <a href="/facts/B-type_star/dYrIuK9H">B-type stars</a>, and are many times more massive and luminous than the Sun. This system was the second ever to be recognized as a binary, in 1685 by a <a href="/facts/Jesuit_priest/n0PeYBB8">Jesuit priest</a>. α1 Crucis is itself a <a href="/facts/Spectroscopic_binary/TYlDe1bD">spectroscopic binary</a> with components designated α Crucis Aa (officially named Acrux, historically the name of the entire system) and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 <a href="/facts/Astronomical_unit/gjsbu5xU">astronomical unit</a> (AU). <a href="/facts/HR_4729/8wNsJu0R">HR 4729</a>, also known as Acrux C, is a more distant companion, forming a triple star through small telescopes. C is also a spectroscopic binary, which brings the total number of stars in the system to at least five. </p>