Small constellation Hydrus can be found in the far southern sky. It initially appeared on a 35-cm (14-in) diameter celestial globe produced in late 1597 (or early 1598) in Amsterdam by Petrus Plancius and Jodocus Hondius. It was one of twelve constellations constructed by Plancius from observations made by Pieter Dirkszoon Keyser and Frederick de Houtman. In Johann Bayer's Uranometria from 1603, this constellation first appeared in a celestial atlas. The brighter stars were catalogued and given Bayer labels in 1756 by the French traveller and astronomer Nicolas Louis de Lacaille. In contrast to Hydra, a considerably larger constellation that symbolises a female water snake, its name means "male water snake." For most observers in the Northern Hemisphere, it is still below the horizon.
The brightest star, Beta Hydri, is 2.8 magnitude, and it is also quite close to the south celestial pole. Gamma Hydri is a fluctuating red giant sixty times the size of the Sun that pulses between magnitude 3.26 and 3.33. One of the brightest dwarf novae in the skies, VW Hydri, is located close by. Exoplanets have been discovered in four Hydrus star systems to date, including HD 10180, which may host up to nine planetary companions. |
History
One of the twelve constellations was named by Dutch astronomer Petrus Plancius based on observations of the southern sky made by Pieter Dirkszoon Keyser and Frederick de Houtman, two Dutch explorers who had travelled to the East Indies on the first Dutch trading expedition, known as the Eerste Schipvaart. It initially appeared in 1598 in Amsterdam on a celestial globe with a diameter of 35 cm (14 in). Plancius and Jodocus Hondius published it. The German cartographer Johann Bayer's 1603 publication Uranometria was the first to feature this constellation in a celestial atlas. De Waterslang, or "The Water Snake" in Dutch, was the name De Houtman gave it when he included it in his southern star catalogue that year, designating a type of snake the expedition encountered rather than a specific snake. On the 1756 version of his planisphere of the southern heavens, the French traveller and astronomer Nicolas Louis de Lacaille referred to it as l'Hydre Mâle to distinguish it from the feminine Hydra. While Lacaille Latinized the name to Hydrus for his updated Coelum Australe Stelliferum in 1763, Jean Fortin kept the French name in 1776 for his Atlas Céleste. |
Characteristics
Inconsistent in shape, Hydrus is bordered to the southeast by Mensa, to the east by Eridanus, to the northeast by Horologium and Reticulum, to the north by Phoenix, to the northwest and west by Tucana, and toe south by Octans; Lacaille had shortened Hydrus' tail to make room for this final constellation he had drawn. It is the 61st largest of the 88 constellations, occupying 243 square degrees and 0.589 percent of the night sky. (Bagnall 2012)
The International Astronomical Union chose the three-letter abbreviation "Hyi" for the constellation in 1922. (Russell 1922) A 12-segment polygon serves as the formal definition of the constellation borders, which were established in 1930 by Belgian astronomer Eugène Delporte. These borders' right ascension values in the equatorial coordinate system range from 00h 06.1m to 04h 35.1m, while their declination coordinates range from 57.85° to 82.06°. In the Northern Hemisphere, it is circumpolar in latitudes north of the 30th parallel and remains below the horizon at latitudes south of the 50th parallel as one of the deep southern constellations. It and Argo Navis are mentioned by Herman Melville in Moby Dick’s "beneath effulgent Antarctic Skies," demonstrating his familiarity with the southern constellations from his whaling expeditions. A position due south can be found by drawing a line from the long axis of the Southern Cross to Beta Hydri, then extending it 4.5 times. (Stilwell 2010) Around October 26, Hydrus reaches its peak at midnight. (Malin & Frew 1995)
Inconsistent in shape, Hydrus is bordered to the southeast by Mensa, to the east by Eridanus, to the northeast by Horologium and Reticulum, to the north by Phoenix, to the northwest and west by Tucana, and toe south by Octans; Lacaille had shortened Hydrus' tail to make room for this final constellation he had drawn. It is the 61st largest of the 88 constellations, occupying 243 square degrees and 0.589 percent of the night sky. (Bagnall 2012)
The International Astronomical Union chose the three-letter abbreviation "Hyi" for the constellation in 1922. (Russell 1922) A 12-segment polygon serves as the formal definition of the constellation borders, which were established in 1930 by Belgian astronomer Eugène Delporte. These borders' right ascension values in the equatorial coordinate system range from 00h 06.1m to 04h 35.1m, while their declination coordinates range from 57.85° to 82.06°. In the Northern Hemisphere, it is circumpolar in latitudes north of the 30th parallel and remains below the horizon at latitudes south of the 50th parallel as one of the deep southern constellations. It and Argo Navis are mentioned by Herman Melville in Moby Dick’s "beneath effulgent Antarctic Skies," demonstrating his familiarity with the southern constellations from his whaling expeditions. A position due south can be found by drawing a line from the long axis of the Southern Cross to Beta Hydri, then extending it 4.5 times. (Stilwell 2010) Around October 26, Hydrus reaches its peak at midnight. (Malin & Frew 1995)
Deep-sky Objects
PGC 6240 – AM 0139-655 – White Rose Galaxy
Large Magellanic Cloud – Extends into Hydrus
NGC 1466 – Globular Cluster
NGC 602 – Open Cluster situated in the Small Magellanic Cloud (Nebula is known by N90)
Main stars - 3
Bayer stars - 19
Stars with planets - 4
Stars brighter than magnitude 3.00 - 2
Stars within 32 Ly - 1
Bordering
constellations
PGC 6240 – AM 0139-655 – White Rose Galaxy
Large Magellanic Cloud – Extends into Hydrus
NGC 1466 – Globular Cluster
NGC 602 – Open Cluster situated in the Small Magellanic Cloud (Nebula is known by N90)
Main stars - 3
Bayer stars - 19
Stars with planets - 4
Stars brighter than magnitude 3.00 - 2
Stars within 32 Ly - 1
Bordering
constellations
- Dorado
- Eridanus
- Horologium
- Mensa
- Octans
- Phoenix
- Reticulum
- Tucana