In this article, we’ll be sharing with you everything you need to know about the constellation of Hydra, including how to find it, deep space objects contained within it and how to use it to find other night sky objects more easily.

The Constellation of Hydra

This constellation was known to several cultures including Ancient Mesopotamia, Ancient Babylon, Hindu and Chinese. Being so obvious, Hydra is one of the constellations that Greek astronomer Ptolemy cataloged over 2,000 years ago and there are two Greek myths associated with it.

The first myth is about Corvus, the Crow. Apollo sent Corvus to fetch him some water in a cup. Corvus became distracted and knowing that Apollo would be angry, made up a story about how a water snake, Hydra, had attacked him and caused the delay.

Corvus returned to Apollo without the water and Apollo was so angry that he put Corvus, Hydra and the cup (Crater) into the heavens where Hydra prevents Corvus from drinking from the cup.

The second myth is about the Twelve Labors of Heracles. Hydra was a giant, multi-headed monster with an immortal head and Heracles’s Second Labor was to kill it. Heracles found Hydra’s lair and lured it out. Every time Heracles cut off one of the monster’s heads, two more heads grew in its place.

When Heracles called to his charioteer, Iolaus, for help, Iolaus started a large fire and began cauterizing the Hydra’s stumps. The cauterized stumps were unable to grow new heads and eventually Heracles was able to cut off the Hydra’s immortal head and bury it under a rock. 

To help you spot Hydra, here’s what SkySafari 6 shows.

Hydra as shown by SkySafari
Hydra as shown by SkySafari. Click for full-screen.

Hydra has an area of 1,303 square degrees making it the largest of the 88 recognized constellations. It’s also the longest constellation with a length of over 100°.

Hydra is usually depicted as a water snake and the constellation resembles a stick snake whose northern head is near Cancer and whose southern tail is between Centaurus and Libra.

The boundaries and neighboring constellations for Hydra
The boundaries and neighboring constellations for Hydra. Click for full-screen.

In the next section discover how to find Hydra.

How To Find Hydra In The Night Sky

Hydra is part of the Hercules family of constellations and is visible to observers at latitudes between +54° and -83°. Northern Hemisphere observers can partially see it from January to April, and can see it in its entirety in May and June.

Southern Hemisphere observers can see it from January to May.

The constellation of Hydra is bordered by the constellations Antila, Cancer, Canis Minor, Centaurus, Corvus, Crater, Leo, Libra, Lupus, Monoceros, Puppis, Pyxis, Sextans and Virgo

Hydra at 10:00 p.m. on the 2nd of May
Hydra at 10:00 p.m. on the 2nd of May. Click for full-screen.

To find Hydra, do a naked-eye search for Regulus (in Leo). Draw an imaginary line ~20° long, from Regulus south through the constellation Sextans then hop ~10° west to Alphard, at the heart of Hydra. Hydra’s head is ~15° northwest and it’s long tail stretches east.

Alternatively, do a naked-eye search for Spica (in Virgo). Extend a 15° arc from Spica to the trapezoid of the constellation Corvus. Draw an imaginary line from Minkar to Kraz (~5°) at the bottom of Corvus then extend this line another 10° east to Gamma Hydrae. Extend the arc another ~15° from Corvus to another trapezoid, which is the constellation Crater (the cup) The tail of Hydra forms a large ‘v’-shape below Corvus and Crater. 

You can measure these distances with your hand at arm’s length.

To find Hydra’s exact position for your location on any night, use software such as Stellarium (free) or SkySafari.

Hydra’s Brightest Stars 

Hydra contains several stars that shine at magnitude five or brighter. You can see them in the rather busy chart below (apologies, but we had to do it this way to show all of the relevant stars) and more details about them below the chart.

The brightest stars of Hydra
The brightest stars of Hydra. Click for full-screen.

Alpha Hydrae (Alphard) – This variable double star is the brightest star in Hydra and marks Hydra’s heart. The magnitude 1.99, orange giant, primary and magnitude 9.70, secondary component are 282.3 arcseconds apart. Alphard is an eruptive variable ranging in magnitude from 1.93 to 2.01. It’s 175 light-years away. ‘Alphard’ means ‘the solitary one’ in Arabic and is a reference to the lack of stars in this region of the sky.

Beta Hydrae – This variable double star is Hydra’s southernmost star and is 365 light-years away. The magnitude 4.28, blue-white giant, primary and magnitude 5.47, secondary component are 0.6 arcseconds apart. 

Gamma Hydrae (Cauda Hydrae, Dhanab al Shuja) – This variable double star is the second brightest star in Hydra and is 132 light-years away. The magnitude 3.00, yellow-orange, giant, primary and magnitude 12.13, secondary component (a line-of-sight coincedence) are 128.3 arcseconds apart. The primary is an eruptive variable ranging in magnitude from 2.94 to 4.02. ‘Cauda Hydrae’ means ‘Hydra’s Tail’ in Latin and ‘Dhanab al Shuja’ means ‘the Snake’s Tail’ in Arabic. 

Delta Hydrae – This double star is 160 light-years away. The magnitude 4.13, white, main sequence, primary and magnitude 10.70, secondary component are 2.7 arcseconds apart. This may be a multiple system.

Epsilon Hydrae – This variable double star is 129 light-years away. The magnitude 3.40, yellow giant, and magnitude 5.00, subgiant, secondary component are 2.8 arcseconds apart. This rotating variable ranges in magnitude from 3.35 to 3.39. A magnitude 6.7, main sequence star, 4.5 arcseconds away is a third component and is also a double star. A fifth component is a dim red dwarf. 

Zeta Hydrae – This magnitude 3.11, orange giant is the third brightest star in Hydra and is 167 light-years away. Its mass is 1.1 Solar masses, its diameter is 20.1 Solar diameters and it’s 18% cooler than the Sun. 

Eta Hydrae This magnitude 4.28, blue-white, main sequence, variable star is 587 light-years away. It’s a pulsating variable whose magnitude ranges from 4.27 to 4.33 over a period of 0.1700 days.

Theta Hydrae – This variable double star is 113 light-years away. The magnitude 3.89, blue-white, main sequence, primary and magnitude 9.89, secondary component are 20.0 arcseconds apart. The primary is an eruptive variable ranging in magnitude from 3.88 to 3.91. This may be a multiple system. 

Iota Hydrae – This magnitude 3.90, orange giant, is 263 light-years away. It’s an erupting variable whose magnitude ranges from 3.87 to 3.91.

Kappa Hydrae – This magnitude 5.05, blue-white, main sequence, star is 436 light-years away. It’s an eruptive variable.

Lambda Hydrae – This double star is 113 light-years away. The magnitude 3.60, yellow-orange giant, primary and magnitude 13.30, secondary component are 0.0 arcseconds apart.

Mu Hydrae – This magnitude 3.81, orange, star is 234 light-years away. It’s an eruptive variable.

Nu Hydrae – This magnitude 3.10, orange giant, is 144 light-years away. Its mass is 1.2 Solar masses, its diameter is 19.8 Solar diameters and it’s 22% cooler than the Sun. 

Xi Hydrae – This variable double star is 130 light-years away. The magnitude 3.53, yellow-orange giant, primary and magnitude 10.70, secondary component are 74.6 arcseconds apart. This is an eruptive variable and may be a multiple system. 

Omicron Hydrae – This magnitude 4.69, blue-white, main sequence, star is 449 light-years away. It’s an eruptive variable. 

Pi Hydrae – This magnitude 3.25, orange giant, is 101 light-years away. Its mass is 1.2 Solar masses, its diameter is 14.1 Solar diameters and it’s 24% cooler than the Sun. 

Rho Hydrae – This double star is 354 light-years away. The magnitude 4.34, blue-white, main sequence, primary and magnitude 11.90, secondary component are 12.1 arcseconds apart. This may be a multiple system. 

Sigma Hydrae – This magnitude 4.44, orange giant, is 373 light-years away. Its mass is 1.2 Solar masses, its diameter is 27.7 Solar diameters and it’s 22% cooler than the Sun.

Tau1 Hydrae – This variable double star is 57 light-years away. The magnitude 4.92, main sequence, primary and magnitude 7.28, secondary component are 67.5 arcseconds apart. The pair form an eclipsing binary. 

Tau2 Hydrae – This variable double star is 518 light-years away. The magnitude 4.55, white, main sequence, primary and magnitude 5.70, secondary component are 67.5 arcseconds apart. This is an eruptive variable. 

Upsilon1 Hydrae – This magnitude 4.11, yellow-orange giant is 264 light-years away. Its mass is 1.1 Solar masses, its diameter is 17.4 Solar diameters and it’s 14% cooler than the Sun.

Upsilon2 Hydrae – This magnitude 4.59, blue-white giant, variable star is 314 light-years away. It’s an eruptive variable whose magnitude ranges from 4.57 to 4.60. 

Phi3 Hydrae – This magnitude 4.50, yellow-orange giant, is 211 light-years away. Its mass is 1.1 Solar masses, its diameter is 10.6 Solar diameters and it’s 17% cooler than the Sun.

Chi1 Hydrae – This double star is 141 light-years away. The magnitude 4.92, yellow-white, subgaint, primary and magnitude 5.70, secondary component are 0.1 arcseconds apart. 

Psi Hydrae – This magnitude 4.94, orange giant, is 231 light-years away. Its mass is 1.2 Solar masses, its diameter is 13.7 Solar diameters and it’s 22% cooler than the Sun.

Omega Hydrae – This magnitude 4.98, orange giant, is 896 light-years away. Its mass is 1.2 Solar masses, its diameter is 56.5 Solar diameters and it’s 42% cooler than the Sun.

U Hydrae – This magnitude 4.92, red star is 677 light-years away. It’s a pulsating, semi-regular variable.

27 Hydrae – This double star is 222 light-years away. The magnitude 4.80, yellow-orange giant, primary and magnitude 7.03, secondary component are 229.1 arcseconds apart. This may be a multiple system. 

Star Hopping From Hydra

Hydra is the starting point for a few well known star hops.

U Hydrae – Identify Alphard. Follow the zigzag of stars east along Hydra’s body until you reach Mu Hydrae (the third star from Alphard) and Nu Hydrae (the fourth star from Alphard). Imagine Mu Hydrae and Nu Hydrae are the base of an isosceles triangle pointing up and ~ 3° tall. U Hydrae is at the third corner of this triangle.

M83 – Identify Gamma Hydrae and Pi Hydrae (~11° farthereast). Imagine Gamma Hydrae and Pi Hydrae are the base of an isosceles triangle pointing down and ~5° tall. M83 is at the third corner of this triangle.

NGC 3242 – Identify Alphard. Follow the zigzag of stars east along Hydra’s body until you reach Mu Hydrae (the third star from Alphard). NGC 3242 is ~ 2° south of Mu Hydrae.

Objects To See Within Hydra

Hydra contains three Messier objects and a few other deep sky objects suitable for small telescope users. 

M48 (NGC 2548) – This open cluster has a magnitude of 5.80 and an apparent size of 30.0 arcminutes. It’s 2511 light-years away and is at right ascension 8h 14m 46s and declination -05° 48’ 52”.

M68 (NGC 4590) – This globular cluster has a magnitude of 7.84 and an apparent size of 11.0 arcminutes. It’s 34,000 light-years away and is at right ascension 12h 40m 36s and declination -26° 51’ 36”.

M83 (NGC 5236) – This spiral galaxy has a magnitude of 7.09 and an apparent size of 13.6 x 13.2 arcminutes. It’s 16 million light-years away and is at right ascension 13h 36m 13s and declination -29° 58’ 23”.

NGC 3109 – This spiral galaxy has a magnitude of 9.70 and an apparent size of 16.0 x 2.7 arcminutes. It’s 4 million light-years away and is at right ascension 10h 04m 05s and declination -26° 15’ 43”.

NGC 3242 (Ghost Of Jupiter, Eye Nebula) – This planetary nebula has a magnitude of 7.30 and an apparent size of 0.7 x 0.6 arcminutes. It’s 1400 light-years away and is at right ascension 10h 25m 47s and declination -18° 28’ 12”.

NGC 3641 – This spiral galaxy has a magnitude of 9.40 and an apparent size of 9.8 x 4.0 arcminutes. It’s 22 million light-years away and is at right ascension 11h 19m 18s and declination -32° 55’ 43”.

Summary

Hydra is the largest constellation and contains lots of bright stars along its long body.

It’s also home to some fabulous deep sky objects for small telescope users to take a look at. Find its heart near Leo and its tail near Corvus and Crater. 

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