Heavenly news: Dance of the constellation — Hydra the Serpent

By From page B2 | April 02, 2012

Nicole Gauthier


The giant celestial snake, Hydra, is slithering into view in the night sky this spring. Look to the south to trace it during the early evening hours.

This long and mostly faint constellation of Hydra, the female water snake, is one of the most extensive of all star patterns. Interestingly, there is also a much shorter, male snake bearing the name Hydrus, which is visible only in the Southern Hemisphere skies.

Hydra begins just below Cancer with a boxy shape of five stars representing the snake’s head, between Procyon and Regulus, and south of the faint constellation Cancer, the Crab.

It is the largest of the 88 modern constellations, measuring 1,303 square degrees and has a long history, having been included among the original 48 constellations listed by the second century astronomer Ptolemy.

The Greek constellation of Hydra is an adaptation of a Babylonian constellation, the MUL.APIN which includes a “serpent” constellation (MUL.DINGIR.MUŠ) loosely corresponding to Hydra. It is one of two Babylonian “serpent” constellations (the other being the origin of the Greek Serpens), a mythological hybrid of serpent, lion and bird.

The constellation Hydra resembles a twisting snake, and is depicted as such in some Greek myths. One time is when Apollo sends a crow to fetch water, but it rests lazily on the journey, and after finally obtaining the water in a cup, takes back a water snake as well, as an excuse.

According to the myth, Apollo saw through the fraud, and angrily cast the crow, cup, and snake, into the sky. The origin of this story is likely to be the juxtaposition of this constellation with those of Crater, and Corvus, in the area of the sky known as the Sea.

The Hydra was also considered to be the Lernaean Hydra (as defeated by Hercules as one of his Twelve Labors) by the Greeks.

Its position in the sky (below the ecliptic), together with the constellation Cancer (which lies near its head) may be the origin of parts of the myth.

Despite its size, Hydra contains only one reasonably bright star, Alphard, which is of apparent magnitude 1.98. Alphard (the solitary one) is actually a double star. The other main named star in Hydra is Minaruja (Arabic for snake’s nose). At magnitude 4.54, it is rather dim. The head of the snake corresponds to the Āshleshā Nakshatra, the lunar zodiacal constellation in Indian astronomy.

There are several double stars of interest in Hydra. Epsilon Hydrae (ε Hya) is a binary star with components of magnitudes 3.3 and 6.8, separated by 2.7 arc seconds. N Hydrae (N Hya) is a pair of stars of magnitudes 5.8 and 5.9. Struve 1270 (Σ1270) consists of a pair of stars, magnitudes 6.4 and 7.4.

Hydra contains three Messier objects. M83 (NGC 5236), also known as the Southern Pinwheel Galaxy, is a barred spiral galaxy approximately 15 million light-years away located on the border of Hydra. It is one of the closest and brightest barred spiral galaxies in the sky, making it visible with binoculars.
Another Messier object found in the constellation Hydra is M68 (NGC 4590), a globular cluster near M83 approximately 33,000 light years from Earth. The third Messier object, M48 (NGC 2548) is an open star cluster in the western end of the serpent. Six supernovae (SN 1923A, SN 1945B, SN 1950B, SN 1957D, SN 1968L and SN 1983N) have been observed in M83.

If you want to learn more about this constellation and other wonders in the springtime night sky, visit the Cameron Park Rotary Club Community Observatory on a clear sky Friday, Saturday or Sunday evening starting at 7:30.

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Nicole Gauthier

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