Hydra

Hydra is the largest of all the constellations, visible in a equatorial and southern evening sky in the months around January and February. It was included among the 48 constellations listed by the 2nd century astronomer Ptolemy.

Named after a water snake, Hydra is a long thin constellation, whose head lies slightly north of the celestial equator, but whose tail dips below a declination of 30°S. The angular distance between the head and tail of the snake is 85°.

Despite its large size, Hydra is a faint constellation with only one star brighter than third magnitude. The snake traces a path roughly parallel to the plane of the Milky Way and roughly 20° to its north. It is home to a few bright deep sky objects, including the open cluster M48, the galaxy M83 and the globular cluster M68.

The Greek constellation of Hydra is an adaptation of a Babylonian constellation which includes a “serpent” constellation that loosely corresponds to Hydra. It is one of two Babylonian “serpent” constellations a mythological hybrid of serpent, lion and bird.

The shape of Hydra resembles a twisting snake, and features as such in some Greek myths. One myth associates it with a water snake that a crow served Apollo in a cup when it was sent to fetch water; Apollo saw through the fraud, and angrily cast the crow, cup, and snake, into the sky. It is also associated with the monster Hydra, with its many heads, killed by Hercules, represented in another constellation. According to legend, if one of the Hydra’s heads was cut off, two more would grow in its place. However, Hercules’ nephew, Iolaus, seared the necks with a torch to prevent them from growing back and thus enabled Hercules to overcome the Hydra. In the sky, however, it is depicted with only one head.

According to another myth, Hydra is the water snake in the tale of the crow and the cup, Corvus and Crater.

In India the constellation is called ಅಜಗರ (Ajagara)

Hydra contains:

• Stars
  • Alphard (mag 2.0)
  • γ-Hya (mag 3.0)
  • ζ-Hya (mag 3.1)
  • ν-Hya (mag 3.1)
  • π-Hya (mag 3.2)
  • ε-Hya (mag 3.4)
  • ξ-Hya (mag 3.5)
  • λ-Hya (mag 3.6)
  • μ-Hya (mag 3.8)
  • θ-Hya (mag 3.9)
  • C-Hya (mag 3.9)
  • ι-Hya (mag 3.9)
  • υ¹-Hya (mag 4.1)
  • δ-Hya (mag 4.1)
  • η-Hya (mag 4.3)
  • D-Hya (mag 4.3)
  • ρ-Hya (mag 4.3)
  • β-Hya (mag 4.4)
  • E-Hya (mag 4.4)
  • σ-Hya (mag 4.4)
  • τ²-Hya (mag 4.6)
  • υ²-Hya (mag 4.6)
  • τ¹-Hya (mag 4.6)
  • F-Hya (mag 4.6)
  • 2-Sex (mag 4.7)
• Open Clusters
  • Messier 48 (mag 5.8)
  • IC 518
• Globular Clusters
  • Messier 68 (mag 7.3)
• Galaxy
  • Messier 83 (mag 7.5)
  • NGC 3402 (mag 9.0)
  • NGC 3621 (mag 9.6)
  • NGC 3923 (mag 9.8)
  • NGC 3585 (mag 10.0)
  • NGC 2935 (mag 10.0)
  • NGC 3109 (mag 10.0)
  • NGC 2784 (mag 10.2)
  • NGC 5061 (mag 10.4)
  • NGC 5101 (mag 10.5)
  • NGC 3091 (mag 10.6)
  • NGC 3311 (mag 10.9)
  • NGC 2986 (mag 10.9)
  • NGC 3904 (mag 11.0)
  • NGC 2835 (mag 11.0)
  • NGC 3078 (mag 11.1)
  • NGC 5085 (mag 11.1)
  • NGC 2811 (mag 11.3)
  • NGC 4106 (mag 11.3)
  • NGC 2865 (mag 11.4)
  • NGC 2781 (mag 11.5)
  • NGC 5078 (mag 11.5)
  • NGC 2983 (mag 11.7)
  • NGC 2713 (mag 11.7)
  • NGC 2962 (mag 11.7)