Costellazione Idra Maschio, stelle principali e mitologia

21 Apr 2018

OSR blog post

L'Idra Maschio, o anche nota come Serpente di Mare e Idra Australe (in latino Hydrus) è una piccola costellazione australe poco appariscente, situata in prossimità della costellazione del Tucano e della Piccola Nube di Magellano. E' stata introdotta da Johann Bayer nell'Uranometria (1603) e non va confusa con la più grande e famosa costellazione dell'Idra.

Main stars of the constellation Male Hydra

The constellation of Male Hydra is not particularly rich in brilliant bodies. However, at least the three stars that create the central triangular perspective of the figure assumed by the constellation are worth mentioning:
– β Hydri is the brightest star, with a magnitude of 2.8 and yellow colour: although very similar to the Sun in its composition , is three times brighter and is, at the same time, among the closest stars observable to the naked eye and, furthermore, the brightest star closest to the South Celestial Pole.
– In second place in terms of brightness is α Hydri, with magnitude 2.9 and white colour: it is close to Achernar, alpha star of the constellation Eridanos.
– The largest star in the constellation is γ Hydri, which is a red giant close to the Large Magellanic Cloud and has a magnitude of 3.2.

There are not many double stars that are particularly noteworthy in this constellation (among them it is possible to mention HD 20313). Variable stars are also very faint (among the brightest is RS Hydri, a Mireid). Among the non-stellar objects of particular importance, we highlight NGC 1466, a globular cluster belonging to the Large Magellanic Cloud.

A separate discussion must be referred to the star HD 10180, a yellow dwarf similar to the Sun: this star is equipped with the largest planetary system known ever, outside the solar system; in particular, according to studies carried out by astronomers, it seems that the planet HD 10180 g is located within the so-called habitable zone.
In particular, ESO astronomers, using the HARPS spectrometer, were able to observe at least five planets orbiting this star; the presence of at least two other planets is also hypothesized. These elements make the HD 10180 system the most similar to the solar system found so far in the cosmos: in fact, the presence of at least five planets of non-gaseous mass is hypothesized (similar to what happens for the solar planets closest to our star). , located at a distance no greater than that, compared to the solar system, of the orbit of Mars.
Finally, of note are η2 Hydri and GJ 3021, stars also equipped with a planetary system.

Mythology of the Male Hydra

Since it is a constellation belonging to the southern hemisphere, its discovery and cataloging is relatively recent. The result is the absence of a mythological link dating back to antiquity, as happens with other constellations. However, it is curious to point out that Bayer’s attribution of the name Hydrus in 1603 derives from the more well-known constellation of Hydra: Bayer, in fact, wanted to consider the Male Hydra as a sort of equivalent to the constellation of the Female Hydra, almost was the southern continuation of the very long constellation Boreal.
According to another reconstruction, however, the name Hydrus was chosen in consideration of the proximity of this group of stars to the constellation of Eridanos: since this takes its name from a river, the toponym of water serpent (or Hydra, precisely) would have derived from it . The fact that the discovery of the constellation does not seem to be attributable to Bayer seems to be in favor of this second reconstruction: in fact, a first mention of it is found in the writings of the cartographer Petrus Plancius, who, reworking the maps sent to him by some Dutch explorers between 1595 and in 1603, he updated the celestial catalog by adding, among others, the constellation of Male Hydra: in the Plancius catalogue, in fact, the Dutch and Latin wording Whaterslange/Hydrus appears.

Characteristics and observation: how to observe Male Hydra

It is a constellation bordering the Octans, particularly located in the extreme south of the celestial panorama (not surprisingly, one of its stars, as seen, is among the closest to the celestial South Pole): although the Hydrus passes the meridian between the end of August and the end of November, its extremely southern location means it constantly occupies an area of ​​sky that is completely inaccessible to the northern temporal latitudes (id east, for Italy). Therefore, in the Northern Hemisphere it is visible internally only a few degrees north of the equator, while it remains totally invisible beyond the Tropic of Cancer.
The shape of the star cluster is essentially that of a water serpent, whose tail touches the Octant in a southerly direction, while the head collides with the star Achernar of Eridanus: the central body of the constellation, given by its brightest stars, is that of a triangle.
Taking into consideration the head and tail of the serpent, the placement of the Male Hydra can also be facilitated thanks to the reference to the Large and Small Magellanic Clouds, which are placed respectively to the left and right of the Dorado and the Toucan: identify the two nebulae, it is possible to see the constellation Hydrus right in the center.

The recommended period for observation, placing live in the southern evening sky, is between the months of October and February. However, being a constellation practically close to the South Celestial Pole, its observation is circumpolar, and therefore almost identical for all the other regions of the southern hemisphere.