A constellation of six stars that can be seen in the southern celestial hemisphere is called Horologium (Latin: hrologium, the pendulum clock; Greek: v, lit. "an instrument for telling the hour"). Nicolas-Louis de Lacaille, a French astronomer, originally described it in 1756. He pictured it as a clock with a pendulum and a second hand. The International Astronomical Union (IAU) redefined the constellation in 1922 and has since recognised it as a region of the celestial sphere comprising Lacaille's stars. Observers south of 23°N can see the entire connected region of Horologium.
Alpha Horologii (at 3.85), an elderly orange giant star that has ballooned to almost 11 times the diameter of the Sun, is the brightest star in the constellation and the only one brighter than an apparent brightness of 4. One of the biggest fluctuations in brightness among all stars in the night sky that are visible to the human eye is found in the long-period variable-brightness star R Horologii (4.7 to 14.3). At least one of the four-star systems in the constellation, Gliese 1061, has an exoplanet in its habitable zone. |
History
After observing and cataloguing about 10,000 southern stars during a two-year sojourn at the Cape of Good Hope, the French astronomer Nicolas Louis de Lacaille named the constellation l'Horloge à pendule & à seconds (Clock with pendulum and seconds hand) in 1756 (Lacaille 1765). In previously unexplored parts of the southern celestial hemisphere that were not visible from Europe, he created fourteen new constellations. The Age of Enlightenment was represented by all but one of them because they honoured scientific tools. In a catalogue and updated chart that was published posthumously in 1763, the constellation's name was Latinized Horologium. (Wagman 2003) The Ancient Greek word "v," which refers to a device for telling the time, is ultimately where the Latin name comes from.
After observing and cataloguing about 10,000 southern stars during a two-year sojourn at the Cape of Good Hope, the French astronomer Nicolas Louis de Lacaille named the constellation l'Horloge à pendule & à seconds (Clock with pendulum and seconds hand) in 1756 (Lacaille 1765). In previously unexplored parts of the southern celestial hemisphere that were not visible from Europe, he created fourteen new constellations. The Age of Enlightenment was represented by all but one of them because they honoured scientific tools. In a catalogue and updated chart that was published posthumously in 1763, the constellation's name was Latinized Horologium. (Wagman 2003) The Ancient Greek word "v," which refers to a device for telling the time, is ultimately where the Latin name comes from.
Characteristics
Horologium is the 58th-largest of the 88 contemporary constellations, taking up a total of 248.9 square degrees, or 0.603 percent, of the sky. Due to its location in the southern celestial hemisphere, observers south of 23°N may see the entire constellation. The five constellations Eridanus (the Po or Nile River), Caelum (the chisel), Reticulum (the reticle), Dorado (the dolphin/swordfish), and Hydrus surround the constellation Horologium (the male water snake). The International Astronomical Union chose the three-letter abbreviation "Hor" for the constellation in 1922. (Russell 1922) A twenty-two-sided polygon serves as the official constellation's border. These borders' right ascension coordinates in the equatorial coordinate system range from 02h 12.8m to 04h 20.3m, while their declination coordinates are −39.64° and −67.04° |
Deep-sky Objects
NGC 1261 – Globular Cluster
Arp-Madore 1 – Globular Cluster
NGC 1512 – Barred Spiral Galaxy
NGC 1510 – Dwarf Lenticular Galaxy
Horologium-Reticulum Supercluster – Galaxy Cluster
Main stars - 6
Bayer stars - 10
Stars with planets - 4
Stars brighter than magnitude 3.00 - 0
Stars within 32 Ly - 1
Bordering
constellations
NGC 1261 – Globular Cluster
Arp-Madore 1 – Globular Cluster
NGC 1512 – Barred Spiral Galaxy
NGC 1510 – Dwarf Lenticular Galaxy
Horologium-Reticulum Supercluster – Galaxy Cluster
Main stars - 6
Bayer stars - 10
Stars with planets - 4
Stars brighter than magnitude 3.00 - 0
Stars within 32 Ly - 1
Bordering
constellations
- Eridanus
- Hydrus
- Reticulum
- Dorado
- Caelum