The Nautical Almanac # 30 --- Acrux (Alpha Crucis)

The thirtieth star of the Nautical Almanac is Acrux or Alpha Crucis, the brightest star of the constellation Crux (The Cross, usually called "The Southern Cross" because it is visible in the southern hemisphere). Acrux is the brightest star in The Southern Cross, and forms the foot of the cross. The Southern Cross is the smallest of the 88 modern constellations. 

The very dark area adjacent to Crux on the star chart is the darkest nebula in the sky, the Coal Sack.

Acrux is a multistar system, made up of four stars in close orbit around each other (Alpha Crucis Beta, the outlier, can be seen as a separate star in powerful telescopes). 

Acrux is a Magnitude 1 star, and the brightest star in the southern sky. It can be seen from Miami, Florida (very close to the horizon) and appears ever higher from points further south. (In ancient days, the constellation Crux could be seen from Britain, but precession has caused it to settle ever lower in the northern sky over thousands of years). Sometimes Acrux is called "Magellan's Star" because the explorer identified it during his circumnavigation, though it was certainly seen by Europeans before the 1500s.

The Acrux system is about 11 million years old. It lies 321 light years from Earth. Alpha Crucis Alpha is about 18 times the mass of our Sun, about 25,000 times the luminosity, and burns at about 45,000 degrees F. All the Acrux stars rotate rapidly, between 270,000 mph and 450,000 mph, making them extremely oblate. It is believed that they exchange mass. The system appears as a giant blue-white star in visual telescopes. 

The Southern Cross (and hence Acrux) appears on the flags of Australia, New Zealand, Samoa, and Papua New Guinea, and also Brazil, where it represents the State of Sao Paulo. 

Crux itself has religious connotations in Christianity, and in several native religions as well, since crosses are very common mystical symbols. In Australia and Oceania the constellation is also seen as a manta ray, an eagle, a swan, a crane, a fish, and a duck by various peoples.