Alpha Crucis

The southernmost of the four bright stars forming the Southern Cross, Acrux sits at a declination of −63°, deep in the constellation Crux and permanently invisible from mid-northern latitudes. Designated Alpha Crucis, it is a blue-white B-type star with a hot, negative B–V index of −0.243. At apparent magnitude 0.77 it is the brightest member of the Cross, and its absolute magnitude of −4.2 confirms a luminosity many times the Sun's, holding its brightness across a distance of about 322 light-years. Acrux is one of the most important navigational stars of the southern celestial hemisphere.