Horologium (constellation)

Horologium (constellation)

Abbreviation Hor
Genitive Horologii
Pronunciation ,
Symbolism the Pendulum Clock
Right ascension 3
Declination −60
Family La Caille
Quadrant SQ1
Area 249 sq. deg. (58th)
Main stars 6
Stars with planets 2
Stars brighter than 3.00m 0
Stars within 10.00 pc (32.62 ly) 1
Brightest star α Hor (3.85m)
Nearest star GJ 1061
(11.99 ly, 3.66 pc)
Messier objects none
Meteor showers ?????
Visible at latitudes between +30° and −90°.
Best visible at 21:00 (9 p.m.) during the month of December.

Horologium is a small and faint constellation in the southern sky (declination around −60 degrees). Its name is a Latin transliteration of the Greek[1] word for clock (ὡρολόγιον, "the hour-teller" from ὥρα hṓra "hour and -λόγιον -logion, "teller"). The constellation was devised by French astronomer Nicolas Louis de Lacaille in 1752, and it remains one of the 88 modern constellations.


  • History 1
  • Characteristics 2
  • Notable features 3
    • Stars 3.1
    • Deep-sky objects 3.2
  • See also 4
  • References 5
  • External links 6


Horologium was one of 14 constellations created by Abbé Nicolas Louis de Lacaille during his expedition to the Cape of Good Hope.[2] He originally labeled it Horologium Oscillitorium, the Latin name for a pendulum clock, to honour its inventor Christiaan Huygens and his book Horologium Oscillatorium.


Horologium is bordered by five different constellations: Eridanus (the Po River), Caelum (the chisel), Reticulum (the reticle), Dorado (the dolphinfish/swordfish), and Hydrus (the male water snake). The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is Hor. The official constellation boundaries are defined by a twenty-two sided polygon. Covering a total of 249 square degrees, Horologium ranks 58th in area out of the 88 modern constellations.

Notable features

The constellation Horologium as it can be seen by the naked eye.


Horologium does not have any bright stars. Alpha Horologii, the brightest, is an orange giant of magnitude 3.9, 117 light-years from Earth. Beta Horologii is a white giant of magnitude 5.0, 314 light-years from Earth. However, Horologium does have several variable stars. R Horologii is a red giant Mira variable with a very wide range, 1000 light-years from Earth. It has a minimum magnitude of 14.3 and a maximum magnitude of 4.7; its period is approximately 13 months.[2]

Deep-sky objects

Horologium is also home to many deep-sky objects; there are several globular clusters in the constellation. NGC 1261 is a globular cluster of 8th magnitude, located 44,000 light-years from Earth.[2] The globular cluster Arp-Madore 1 is found in the constellation, the most remotely known globular cluster in the Milky Way at a distance of 398,000 light years.

See also


  1. ^ Smith, William (1875). A Dictionary of Greek and Roman Antiquities. London: John Murray. pp. 615‑617. 
  2. ^ a b c Ridpath & Tirion 2001, pp. 156-157.
  • Ridpath, Ian; Tirion, Wil (2001), Stars and Planets Guide,  
  • Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.

External links

  • The Deep Photographic Guide to the Constellations: Horologium
  • Starry Night Photography - Horologium Constellation
  • Star Tales – Horologium
  • Horologium Constellation at Constellation Guide