Hydrus

Coordinates: Sky map 02h 00m 00s, −70° 00′ 00″
Source: Wikipedia, the free encyclopedia.
For other uses, see Hydrus (disambiguation). Not to be confused with the equatorial constellation of Hydra.
"Hyi" redirects here. For other uses, see HYI.

Hydrus
Constellation
61st)
Main stars3
Bayer/Flamsteed
stars		19
Stars with planets4
Stars brighter than 3.00m2
Stars within 10.00 pc (32.62 ly)1
Brightest starβ Hyi (2.82m)
Messier objectsnone
Meteor showersnone
Bordering
constellations		Dorado
Eridanus
Horologium
Mensa
Octans
Phoenix (corner)
Reticulum
Tucana
Visible at latitudes between +8° and −90°.
Best visible at 21:00 (9 p.m.) during the month of November.

Hydrus

southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first appeared on a 35-cm (14 in) diameter celestial globe published in late 1597 (or early 1598) in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756. Its name means "male water snake", as opposed to Hydra, a much larger constellation that represents a female water snake. It remains below the horizon for most Northern Hemisphere
observers.

The brightest star is the 2.8-magnitude Beta Hydri, also the closest reasonably bright star to the south celestial pole. Pulsating between magnitude 3.26 and 3.33, Gamma Hydri is a variable red giant 60 times the diameter of the Sun. Lying near it is VW Hydri, one of the brightest dwarf novae in the heavens. Four star systems in Hydrus have been found to have exoplanets to date, including HD 10180, which could bear up to nine planetary companions.

History

Hydrus (lower right) in an extract from Johann Bayer's Uranometria, its first appearance in a celestial atlas.

Hydrus was one of the twelve constellations established by the Dutch astronomer

Eerste Schipvaart, to the East Indies. It first appeared on a 35-cm (14 in) diameter celestial globe published in late 1597 (or early 1598) in Amsterdam by Plancius with Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in the German cartographer Johann Bayer's Uranometria of 1603.[2][3] De Houtman included it in his southern star catalogue the same year under the Dutch name De Waterslang, "The Water Snake",[4] it representing a type of snake encountered on the expedition rather than a mythical creature.[5] The French explorer and astronomer Nicolas Louis de Lacaille called it l’Hydre Mâle on the 1756 version of his planisphere of the southern skies, distinguishing it from the feminine Hydra. The French name was retained by Jean Fortin in 1776 for his Atlas Céleste, while Lacaille Latinised the name to Hydrus for his revised Coelum Australe Stelliferum in 1763.[6]

Characteristics

Irregular in shape,

Moby Dick "beneath effulgent Antarctic Skies", highlighting his knowledge of the southern constellations from whaling voyages.[10] A line drawn between the long axis of the Southern Cross to Beta Hydri and then extended 4.5 times will mark a point due south.[11] Hydrus culminates at midnight around 26 October.[12]

Features

The constellation Hydrus as it can be seen by the naked eye

Stars

See also: List of stars in Hydrus

Keyzer and de Houtman assigned fifteen stars to the constellation in their Malay and Madagascan vocabulary, with a star that would be later designated as Alpha Hydri marking the head, Gamma the chest and a number of stars that were later allocated to Tucana, Reticulum, Mensa and Horologium marking the body and tail.[13] Lacaille charted and designated 20 stars with the Bayer designations Alpha through to Tau in 1756. Of these, he used the designations Eta, Pi and Tau twice each, for three sets of two stars close together, and omitted Omicron and Xi. He assigned Rho to a star that subsequent astronomers were unable to find.[14]

Beta Hydri, the brightest star in Hydrus, is a yellow star of

luminosity class of 'IV' indicating this is a subgiant star. As such, it is a slightly more evolved star than the Sun, with the supply of hydrogen fuel at its core becoming exhausted. It is the nearest subgiant star to the Sun and one of the oldest stars in the solar neighbourhood. Thought to be between 6.4 and 7.1 billion years old, this star bears some resemblance to what the Sun may look like in the far distant future, making it an object of interest to astronomers.[16] It is also the closest bright star to the south celestial pole.[7]

Located at the northern edge of the constellation and just southwest of Achernar is Alpha Hydri,[17] a white sub-giant star of magnitude 2.9, situated 72 light-years from Earth.[18] Of spectral type F0IV,[19] it is beginning to cool and enlarge as it uses up its supply of hydrogen. It is twice as massive and 3.3 times as wide as the Sun and 26 times more luminous.[18] A line drawn between Alpha Hydri and Beta Centauri is bisected by the south celestial pole.[12]

In the southeastern corner of the constellation is

rotation period—in this case 113.6 minutes.[25]

There are two notable optical double stars in Hydrus. Pi Hydri, composed of

Pi2 Hydri, is divisible in binoculars.[7] Around 476 light-years distant,[26] Pi1 is a red giant of spectral type M1III that varies between magnitudes 5.52 and 5.58.[27] Pi2 is an orange giant of spectral type K2III and shining with a magnitude of 5.7, around 488 light-years from Earth.[28]

Eta Hydri is the other optical double, composed of Eta1 and Eta2.[7] Eta1 is a blue-white main sequence star of spectral type B9V that was suspected of being variable,[29] and is located just over 700 light-years away.[30] Eta2 has a magnitude of 4.7 and is a yellow giant star of spectral type G8.5III around 218 light-years distant,[31] which has evolved off the main sequence and is expanding and cooling on its way to becoming a red giant. Calculations of its mass indicate it was most likely a white A-type main sequence star for most of its existence, around twice the mass of the Sun. A planet, Eta2 Hydri b, greater than 6.5 times the mass of Jupiter was discovered in 2005, orbiting around Eta2 every 711 days at a distance of 1.93 astronomical units (AU).[32]

Three other systems have been found to have planets, most notably the Sun-like star HD 10180, which has seven planets, plus possibly an additional two for a total of nine—as of 2012 more than any other system to date, including the Solar System.[33] Lying around 127 light-years (39 parsecs) from the Earth,[34] it has an apparent magnitude of 7.33.[35]

GJ 3021 b). Orbiting about 0.5 AU from its star, it has a minimum mass 3.37 times that of Jupiter and a period of around 133 days.[37] The system is a complex one as the faint star GJ 3021B orbits at a distance of 68 AU; it is a red dwarf of spectral type M4V.[38]

HD 20003 is a star of magnitude 8.37. It is a yellow main sequence star of spectral type G8V a little cooler and smaller than the Sun around 143 light-years away. It has two planets that are around 12 and 13.5 times as massive as the Earth with periods of just under 12 and 34 days respectively.[39]

Deep-sky objects

Hydrus contains only faint deep-sky objects. IC 1717 was a deep-sky object discovered by the Danish astronomer John Louis Emil Dreyer in the late 19th century. The object at the coordinate Dreyer observed is no longer there, and is now a mystery. It was very likely to have been a faint comet.[40] PGC 6240, known as the White Rose Galaxy, is a giant spiral galaxy surrounded by shells resembling rose petals, located around 345 million light years from the Solar System. Unusually, it has cohorts of globular clusters of three distinct ages suggesting bouts of post-starburst formation following a merger with another galaxy.[41] The constellation also contains a spiral galaxy, NGC 1511, which lies edge on to observers on Earth and is readily viewed in amateur telescopes.[12]

Located mostly in Dorado, the Large Magellanic Cloud extends into Hydrus.[42] The globular cluster NGC 1466 is an outlying component of the galaxy, and contains many RR Lyrae-type variable stars. It has a magnitude of 11.59 and is thought to be over 12 billion years old.[43] Two stars, HD 24188 of magnitude 6.3 and HD 24115 of magnitude 9.0, lie nearby in its foreground.[12] NGC 602 is composed of an emission nebula and a young, bright open cluster of stars that is an outlying component on the eastern edge of the Small Magellanic Cloud,[44] a satellite galaxy to the Milky Way. Most of the cloud is located in the neighbouring constellation Tucana.[45]

See also

  • Hydrus (Chinese astronomy)

References

  1. ^ a b c "Hydrus, Constellation Boundary". The Constellations. Retrieved 11 September 2013.
  2. ^ Ridpath, Ian. "Johann Bayer's Southern Star Chart". Star Tales. self-published. Retrieved 23 August 2013.
  3. ^ "Hydrus (Water Snake)". Chandra X-ray Observatory. Retrieved 10 July 2012.
  4. ^ Ridpath, Ian. "Frederick de Houtman's Catalogue". Star Tales. self-published. Retrieved 11 September 2013.
  5. ^ a b Ridpath, Ian. "Hydrus—the Lesser Water Snake". Star Tales. self-published. Retrieved 29 September 2013.
  6. ^ Ridpath, Ian. "Lacaille's Southern Planisphere of 1756". Star Tales. self-published. Retrieved 29 September 2013.
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  15. ^ "Beta Hydri". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 11 September 2013.
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  18. ^ a b Kaler, Jim. "Alpha Hydri". Stars. University of Illinois. Retrieved 12 September 2013.
  19. ^ "LTT 1059—High Proper-motion Star". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 12 September 2013.
  20. ^ "Gamma Hydri—Variable Star". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 12 September 2013.
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  22. ^ Kaler, Jim. "Gamma Hydri". Stars. University of Illinois. Retrieved 12 September 2013.
  23. ^ a b BSJ (19 July 2010). "VW Hydri". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 September 2013.
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  26. ^ "HR 667". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 12 September 2013.
  27. ^ "NSV 767". International Variable Star Index. AAVSO. 18 January 2010. Retrieved 12 September 2013.
  28. ^ "HR 678". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 12 September 2013.
  29. ^ "Eta1 Hydri". International Variable Star Index. AAVSO. 4 January 2010. Retrieved 12 September 2013.
  30. ^ "Eta 1Hydri—Variable Star". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 12 September 2013.
  31. ^ "HR 570—Star". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 27 September 2013.
  32. S2CID 6362483
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  33. S2CID 15876919
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  34. ^ Gill, Victoria (24 August 2010). "Rich exoplanet system discovered". BBC News. Retrieved 24 August 2010.
  35. ^ "HD 10180—Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 13 September 2013.
  36. ^ "HD 1237—Pre-main sequence Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 28 September 2013.
  37. S2CID 16606841
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  38. S2CID 16950822
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  39. arXiv:1109.2497 [astro-ph.EP
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  41. S2CID 12557470
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  43. ISBN 978-0-521-48070-3
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  44. ISBN 978-1-4419-1777-5
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  45. ISBN 978-0-521-58582-8
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