Horologium (constellation)
Constellation | |
58th) | |
Main stars | 6 |
---|---|
Bayer/Flamsteed stars | 10 |
Stars with planets | 4 |
Stars brighter than 3.00m | 0 |
Stars within 10.00 pc (32.62 ly) | 1 |
Brightest star | α Hor (3.85m) |
Messier objects | 0 |
Meteor showers | 0 |
Bordering constellations | Eridanus Hydrus Reticulum Dorado Caelum |
Visible at latitudes between +30° and −90°. Best visible at 21:00 (9 p.m.) during the month of December. |
Horologium (Latin hōrologium, the pendulum clock, from Greek ὡρολόγιον, lit. 'an instrument for telling the hour') is a constellation of six stars faintly visible 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
History
The French astronomer Nicolas-Louis de Lacaille first described the constellation as l'Horloge à pendule & à secondes (Clock with pendulum and seconds hand) in 1756,[3][4] after he had observed and catalogued almost 10,000 southern stars during a two-year stay at the Cape of Good Hope. He devised fourteen new constellations in previously uncharted regions of the southern celestial hemisphere, which were not visible from Europe. All but one honoured scientific instruments, and so symbolised the Age of Enlightenment.[a] The constellation name was Latinised to Horologium in a catalogue and updated chart published posthumously in 1763.[5] The Latin term is ultimately derived from the Ancient Greek ὡρολόγιον, for an instrument for telling the hour.[6]
Characteristics
Covering a total of 248.9
Features
Stars
Horologium has one star brighter than apparent magnitude 4,[10] and 41 stars brighter than or equal to magnitude 6.5.[c][7] Lacaille charted and designated 11 stars in the constellation, giving them the Bayer designations Alpha (α Hor) through Lambda Horologii (λ Hor) in 1756. In the mid-19th century, English astronomer Francis Baily removed the designations of two—Epsilon and Theta Horologii—as he held they were too faint to warrant naming. He was unable to find a star that corresponded to the coordinates of Lacaille's Beta Horologii. Determining that the coordinates were wrong, he assigned the designation to another star. Kappa Horologii, too, was unable to be verified—although it most likely was the star HD 18292—and the name fell out of use. In 1879, American astronomer Benjamin Apthorp Gould assigned designations to what became Mu and Nu Horologii as he felt they were bright enough to warrant them.[5]
At magnitude 3.9, Alpha Horologii is the brightest star in the constellation, located 115 (± 0.5)
At magnitude 4.93, Delta Horologii is the second-brightest star in the constellation,[17] and forms a wide optical double with Alpha.[18] Delta itself is a true binary system composed of a white main sequence star of spectral type A5V that is 1.41 times as massive as the Sun with a magnitude of 5.15 and its fainter companion of magnitude 7.29.[19] The system is located 179 (± 4) light-years from the earth.[12]
At magnitude 5.0, Beta Horologii is a
With a magnitude of 5.24,[22] Nu Horologii is a white main sequence star of spectral type A2V located 169 (± 1) light-years from Earth[23] that is around 1.9 times as massive as the Sun. Estimated to be around 540 million years old, it has a debris disk that appears to have two components: an inner disk is orbiting at a distance of 96+9
−37 AU, while an outer disk lies 410+24
−96 AU from the star. The estimated mass of the disks is 0.13%±0.07% the mass of the Earth.[22]
Horologium has several variable stars. R Horologii is a red giant Mira variable with one of the widest ranges in brightness known of stars in the night sky visible to the unaided eye.[24] It is around 1,000 light-years from Earth.[25] It has a minimum magnitude of 14.3 and a maximum magnitude of 4.7, with a period of approximately 13 months.[26] T and U Horologii are also Mira variables.[18] The Astronomical Society of Southern Africa reported in 2003 that observations of these two stars were needed as data on their light curves was incomplete.[27] TW Horologii is a semiregular variable red giant star that is classified as a carbon star,[26] and is 1,370 (± 70) light-years from Earth.[28]
With an apparent magnitude of 13.06,
Deep-sky objects
Horologium is home to many deep-sky objects, including several globular clusters. NGC 1261 is a globular cluster of magnitude 8, located 53,000 light-years from Earth.[26] It lies 4.7 degrees north-northeast of Mu Horologii.[37] The globular cluster Arp-Madore 1 is the most remote known globular cluster in the Milky Way at a distance of 123.3 kiloparsecs (402,000 light-years) from Earth.[38]
The Horologium-Reticulum Supercluster is a galaxy supercluster, second in size only to the Shapley Supercluster in the local universe (anything within 200 mpc of Earth). It contains over 20 Abell galaxy clusters and covers more than 100 deg2 of the sky, centered roughly at equatorial coordinates α = 03h 19m , δ = 50° 2′.[40]
See also
- Horologium (Chinese astronomy)
Notes
- ^ The exception is Mensa, named for Table Mountain. The other twelve (alongside Horologium) are Antlia, Caelum, Circinus, Fornax, Microscopium, Norma, Octans, Pictor, Pyxis, Reticulum, Sculptor and Telescopium.[5]
- ^ While parts of the constellation technically rise above the horizon to observers between the latitudes of 23°N and 50°N, those stars within a few degrees of the horizon are difficult to see.[7]
- ^ Objects of magnitude 6.5 are among the faintest visible to the unaided eye from locations between suburban and rural areas in night skies.[11]
References
- ^ "Horologium". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 2020-03-22.
- ^ a b IAU, The Constellations, Horologium.
- ^ Ridpath, Ian. "Horologium". Star Tales. Self-published. Retrieved 3 September 2020.
- ^ Lacaille, Nicolas Louis (1756). "Relation abrégée du Voyage fait par ordre du Roi au cap de Bonne-espérance". Mémoires de l'Académie Royale des Sciences (in French): 519–592 [588]. Retrieved 2016-03-19.
- ^ ISBN 978-0939923786.
- ^ "horologe, noun". Oxford English Dictionary. Retrieved 26 December 2019. (subscription required)
- ^ a b c d Ridpath, Ian. "Constellations: Andromeda–Indus". Star Tales. self-published. Retrieved 3 September 2020.
- Bibcode:1922PA.....30..469R.
- ^ "Horologium, Constellation Boundary". The Constellations. International Astronomical Union. Retrieved 3 September 2020.
- ISBN 978-0521585828.
- ^ Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Archived from the original on 25 September 2010. Retrieved 1 August 2015.
- ^ S2CID 18759600.
- ^ Ridpath, Ian. "Horologium". Star Tales. self-published. Retrieved 3 September 2020.
- ^ Kaler, Jim. "Alpha Horologii". James Kaler's Stars. Retrieved 3 September 2020.
- .
- ^ S2CID 118665352.
- ^ a b Kaler, Jim (21 January 2011). "Beta Horologii". James Kaler's Stars. Archived from the original on 17 April 2019. Retrieved 20 September 2019.
- ^ ISBN 978-0750306546.
- S2CID 14878976.
- .
- S2CID 119273474.
- ^ S2CID 119211833. 5.
- .
- ISBN 978-1461476481. Archivedfrom the original on 2016-03-28. Retrieved 2016-03-18.
- .
- ^ ISBN 978-0-00-823927-5.
- Bibcode:2003MNSSA..62..234C.
- .
- S2CID 118495267.
- .
- S2CID 18047352.
- S2CID 53694238.
- .
- S2CID 59467665.
- S2CID 53647627.
- S2CID 199551874.
- ^ ISBN 978-1441917775.
- .
- S2CID 9329781.
- S2CID 13839289.
Works cited
- "Horologium". The Constellations. International Astronomical Union.
External links
- The Deep Photographic Guide to the Constellations: Horologium
- The clickable Horologium
- Starry Night Photography – Horologium Constellation