Hydra

IAU Hydra chart

One of the 88 IAU constellations. The name "Hydra" refers to a watersnake from Greek mythology. Still, the underlying constellation originally referred to a Babylonian creature that consisted of a dog-headed snake with wings, the MUŠ.

Etymology and History

The Greek constellation of the Water Snake is a derivative of the Babylonian constellation of the MUŠ-Dragon, a dog-headed creature with the body of a gigantic snake with front legs and wings.

Origin of Constellation

The Babylonian constellation is mentioned as early as 2nd millennium BCE; it occurs in lexical texts and texts of the Three Stars Each-genre. It is also mentioned in the first list (uranology) of MUL.APIN, where the Raven (or Crow) is mentioned at the tip of tail of the huge creature in the sky.

Aratus

The Greek poet Aratus has many Babylonian references; some of them hidden. For him, this constellation is a (Greek) watersnake.

• [443] Another constellation trails beyond, which men call the Hydra. Like a living creature it winds afar its coiling form. Its head comes beneath the middle of the Crab, its coil beneath the body of the Lion, and its tail hangs above the Centaur himself. Midway on its coiling form is set the Crater, and at the tip the figure of a Raven [Corvus] that seems to peck at the coil.
• [449] There, too, by the Hydra beneath the Twins brightly shines Procyon. [51x] and the coil of the gleaming Hydra: in it, too, the dim-lit Crater and the Crow and the scanty-starred Claws and the knees of Ophiuchus are borne.
• [595] Up rises the Hydra’s head and the bright-eyed Hare and Procyon and the forefeet of the flaming dog.
• [600] The Hydra rises higher as far as Crater, and before her the Dog brings up his hind feet, dragging behind him the stern of Argo of many stars.
• [607] Nor can the rising Claws [Libra], though faintly shining, pass unremarked, when at a bound the mighty sign of Boötes rises, jeweled with Arcturus. Aloft is risen all of Argo, but the Hydra, shed as she is afar over the heavens, will lack her tail.
• [663] So she is borne towards the West, but other signs in the East the vault of heaven brings from below, the remaining half of the Crown and the tail of the Hydra, and uplifts the body and head of the Centaur and the Beast that the Centaur holds in his right hand. But the fore-feet of the Centaur-Knight await the rising of the Bow. => pi Hya gehört für Aratus dazu But she sinks beneath the verge the coiling neck and all the brow of the gleaming Hydra.
• [700] Yet many a coil of the Hydra remains, but Night engulfs her wholly with the Centaur, when the Fishes [Pisces] rise; with the Fishes the Fish which is placed beneath azure Aegoceros rises

Hipparchus

Greek	German	English
	weiter giebt Eudoxos auch die auf den sogenannten Kolurkreisen gelegenen Sterne an und behauptet, auf dem einen derselben liege die M:itte des Großen Bären, die Mitte des Kreises, der Nacken der Wasserschlange und von der Argo das Stück zwischen dem Hinterteil und dem Mastbaum; alsdann nach dem unsichtbaren Pol der Schwanz des südlichen Fisches, die Mitte des Steinbocks und die Mitte des Pfeils; endlich gehe er durch den Hals und den rechten Flügel des Schwans, durch die linke Hand des Kepheus, durch die Windung der Shlange und vorbei am Schwanze des Kleinen Bären.		Lib. I. Cap. XL § 9 .
	Ersichtlich macht er dies auch bei dem Aufgange der Fische, wo er sich also ausdrückt; nachdem er nämlich von der Wasserschlange gesagt, daß das Stück vom Kopfe bis zur ersten Windung, wenn der Wassermann im Aufgange begriffen ist, nicht mehr über dem Horizont sei, während den Rest ihres Körpers die Fische hinabführen.		Lib. II. Cap. I. § 24
	Untergang des Perseus, mitkulminierend: Leo 5 1/2: Von der Wasserschlange der vierte von den vier hinter dem hellen nach Osten gelegenen (λ2), 1 Mbr. westlich des Meridians.
	Aufgang des Kentaur, mitkulminierend: Cnc 12°: Von der Wasserschlange der nachfolgende in der südlichen Kinnlade (η)		Lib. III. Cap. I. § 4.
	Untergang Kleiner Hund, mitkulminierend: 3 . Von der Wasserschlange der am Ende des Schwanzes (π).		Lib. III. Cap. n. § 13
	Aufgang der Jungfrau, mitkulminierend: 2. Von der Wasserschlange der nördlichere von denen im Rachen (δ) , 1 Mbr. östlich des Meridians.		Lib. HI. Cap. III. § 3
	Aufgang des Skorpions, mitkulminierend: Von der Wasserschlange von den vieren nach dem hellsten [vor dem Becher] der dritte von Westen (ν2 Hydrae)		Lib. III. Cap. III. § 5.

The mathematical astronomer mentions this constellation rising and setting.

Greek	German	English
	Der nördlichere von denen im Rachen (δ).
	Der aro Ende des Schwanzes (π)

• The first star rising is ,
• the last star rising is the one at the tip of the tail (ὁ ἐν ἄκρᾳ τῇ οὐρᾷ).

Dauer des Aufgangs : 7 1/15 St. = 424m = 106°.

Further stars mentioned

Greek (Manitius 1894)	German (Manitius 1894)	English (...)
	Von der Wasserschlange

Almagest

Greek (Heiberg 18xx)		English (Toomer 1984)	ident.
	1	The 5 stars in the head: the southernmost_of the 2 advance ones, which is on the nostrils	sig  Hya
	2	The 5 stars in the head: the northernmost of these [2], which is above the eye	delta Hya
	3	The 5 stars in the head: the northernmost of the 2 to tl1e rear ofthese, which is about on the skull	eps Hya
	4	The 5 stars in the head: the southernmost of them, on the gaping jaws	eta Hya
	5	The 5 stars in the head: the reannost of all, about on the cheek	zet Hya
	6	The more advanced ofthe 2 star~ in the place where the neckjoins [the head)	omega Hya
	7	The rearmost of them	theta Hya
	8	The middle star of the following three in the bend of the neck	tau2 Hya
	9	The rearmost of the 3	iota Hya
	10	The southernmost of them	tau1 Hya
	11	The faint, northernmost star of the 2 close tagether to the south	BSC 3750
	12	The bright one of these two close stars	alpha Hya
	13	The most advanced ofthe 3 stars to the rear, afl:er the bend [in the neck	kappa Hya
	14	The middle one	upsilon1 Hya
	15	The rearmost of the three	upsilon2 Hya
	16	The most advanccd of the ncxt 3 stars almost on a straight line	mu Hya
	17	The middle one	phi Hya
	18	The rearmost of the three	nu Hya
	19	The northernmost of the 2 stars aher [i.c.  to the rear o.t]  the base of Crater	beta Crt
	20	The southernmost of thcm	chi1 Hya
	21	The most advanced of the 3 stars aller these, as it werc in a triangle	xi Hya
	22	The middle and southernmost onc	omicron Hya
	23	The rearmost of the three	beta Hya
	24	The star after Corvus, in the scction by the tail	gamma Hya
	25	The star on the tip of the tail	pi Hya
Stars round Hydra outside the constellation:
	26	The star to the south of the head	BSC 3314
	27	The star some distance to the rear of those in the neck [ nos. 6-I5]	epsilon Sex

Transfer and Transformation of the Constellation

• 

  the Babylonian version of the "Hydra and Corvus" super-constellation does not contain a cup or jar. visualized in Stellarium (drawing by Jessica Gullberg)

• 

  the lonely star in front of the dragon-head (Procyon) rised simultaneously with the faint stars of The Crab in ancient Babylon. Procyon and the head / foot of the dragon may serve as a replacement for Cancer

• 

  Leo and Virgo above the MUŠ-Dragon, two claytablet drawings from the Seleucid era (roughly 2nd century BCE), CC BY SMH based upon the drawings by E. Weidner (1967) and Thureau-Dangin (1922).

• 

  The Greeks introduced a Crater atop the snake. On the Farnese Globe, the body of the snake forms a vessel for Corvus and Crater.

• 

  In early modern time, some scholars extended the snake-body of Hydra beyond pi Hydrae and placed a second bird (Solitaire or Noctua) at this new end.

IAU WGSN

The star pi Hydrae is very important in history as it is one of the keywitnesses for transfer from Hipparchus to Ptolemy.

• name in Hipparchus: ὁ ἐν ἄκρᾳ τῇ οὐρᾷ (the one at the farthest point of the tail)
• name in the Almagest: ὁ ἐπ᾽ἄκρας τῆς οὐρᾶς (the one at the end of the tail)

The Greek term ἄκρᾳ can be translated as "at the farthest point" or "at the end" (or "hightest" which doesn't apply here).

References

• References (general)
• References (Babylonian)
• References (ancient Greco-Roman)
• References (medieval)