Horologium is a small, inconspicuous constellation in the southern hemisphere. It was charted by the French astronomer Nicolas Louis de Lacaille in the 18th century. The constellation's original name was Horologium Oscillitorium, meaning "the pendulum clock." It was named in honour of Christiaan Huygens, the Dutch horologist and scientist who invented the device in the 17th century and is also famous for discovering Saturn's rings. The name of the constellation was later shortened to Horologium, or the Clock.
The constellation Horologium occupies an area of 249 square degrees and contains one star with known planets. It can be seen at latitudes between +30° and -90° and is best visible at 9 p.m. during the month of December.
The brightest star in the constellation is 
alpha Horologii, a giant star 177 light-years distant from Earth. 
delta Horologii, the second brightest star, is a binary star with a massive white subgiant for its primary component. The star is almost visible with the naked eye, but at 175 light-years' distance, it is quite difficult to spot. 
beta Horologii is a metallic-line star, a chemically peculiar A-type giant. 
R Horologii or HD 18242 is a red giant 100 light-years distant, notable for being a Mira variable, with a pulsation period of 407.6 days.
The constellation is also known for the insufficiently studied Horologium Supercluster, a massive supercluster that stretches approximately 550 million light-years across and contains about 5,000 galaxy groups. It is also known as the Horologium-Reticulum Supercluster. It lies 900 million light-years away from the Milky Way.
Horologium belongs to the Lacaille family of constellations, along with Norma
Constellations directly bordering Horologium are Eridanus