Horologium (constellation)

Common card · No. 436913

Horologium (Latin hōrologium, the pendulum clock, from Greek ὡρολόγιον, lit. 'an instrument for telling the hour') is a faint constellation in the southern celestial hemisphere. It was first described by the French astronomer Nicolas-Louis de Lacaille in 1756 and visualized by him as a clock with a pendulum and a second hand. In 1922 the constellation was redefined by the International Astronomical Union (IAU) as a region of the celestial sphere containing Lacaille's stars, and has since been an IAU designated constellation. Horologium's associated region is wholly visible to observers south of 23°N. The constellation's brightest star—and the only one brighter than an apparent magnitude of 4—is Alpha Horologii (at 3.85), an aging orange giant star that has swollen to around 11 times the diameter of the Sun. The long-period variable-brightness star, R Horologii (4.7 to 14.3), has one of the largest variations in brightness among all stars in the night sky visible to the unaided eye. Four...

Read on Wikipedia · Image IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg), CC BY 3.0