The Constellation: Crux
The constellation Crux “the Cross” (also referred to as “the Southern Cross”) is the smallest constellation in the sky but it has held an important place in the history of the southern hemisphere. The brilliant cross is formed by bright stars making it one of the most familiar sights to southern hemisphere observers. The constellation has been used as insignia on the flags and stamps of many southern hemisphere nations, including Australia, New Zealand, Brazil, Papua New Guinea and regions of Chile and Argentina.
Crux was visible to the Ancient Greeks, who regarded it as part of the constellation Centaurus. At the latitude of Athens in 1000 BC, Crux was clearly visible, though low in the sky. However, the precession of the equinoxes gradually lowered Crux’s stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By AD 400, most of the constellation never rose above the horizon for Athenians. The stars were ‘rediscovered’ by European navigators who explored the southern territories in the early 16th century during the Age of Discovery. Crux was first described as a separate constellation by the Italian explorer Andreas Corsali in 1516. The Portuguese while rounding Africa mapped it and discovered its nautical use. The cross serves as a convenient pointer to the south celestial pole, making it useful in navigation. The brightest star in Crux, Alpha Cruxis, is a binary, or double star.
Can you find Crux?
The constellation Crux (also known as the asterism of the Southern Cross) is easily visible from the southern hemisphere at practically any time of year. For locations south of 34°S, Crux is circumpolar and thus always visible in the night sky. It is also visible near the horizon from tropical latitudes of the northern hemisphere for a few hours every night during the northern winter and spring.
Crux is bordered by the constellations Centaurus (the Centaur), which surrounds it on three sides, and Musca (the Fly). Centaurus is one of the brightest and largest constellations in the southern sky. The two brightest stars in Centaurus, Alpha and Beta Centauri, are often referred to as the “Southern Pointers” or just “The Pointers”, allowing people to easily find the constellation of Crux. (Alpha Centauri is also the 4th brightest star in the night sky.)
Crux is sometimes confused with the nearby False Cross by stargazers. Crux is somewhat kite-shaped, and it has a fifth star (α Crucis). The False Cross is also diamond-shaped, somewhat dimmer on average, does not have a fifth star and lacks the two prominent Pointer stars.