What stars are in the constellation Hydra?

23 January 2012

Above: Image © Torsten Bronger

Have you ever found yourself on a hot date, staring up at the night sky and wishing you could impress the object of your affection by pointing out the stars that connect to form the shape of Orion or Hercules, only to be completely confounded by the thousands of stars you see up there?

Most of us - whether to impress our date or not - have at some point or another wanted to be able to recognize at least a few of the constellations of the night sky, if only to help us navigate our way back to safety if we ever find ourselves washed ashore on a desert island... Okay, so it'd just be cool to know a constellation or two.

Constellations are groupings of stars that seem to resemble a figure or design like animals, objects or mythological creatures. Now you might be thinking "Wait a second. I already know a constellation - the Big Dipper!" - the one that looks like a kitchen pot!

But unfortunately for you, and contrary to popular belief, the Big Dipper is not, in fact, a constellation at all. It's actually what's called an asterism, an easily recognizable pattern of stars within a constellation; the Big Dipper forms the rear end and tail of the constellation Ursa Major, the big bear. Other well-known asterisms include the Summer Triangle and the Northern Cross.

As far as bona fide constellations go, there are a total of 88 official ones recognized by modern astronomers, which may sound daunting to a novice stargazer, but if you step outside tonight and focus your gaze toward the southern horizon, chances are you'll be staring at one in particular: Hydra (pronounced HIGH-druh).

The History of Hydra

Hydra is an interesting, although less well-known constellation for a number of reasons. For one, it's one of the surviving constellations of the ancient world that were catalogued by the Roman astronomer Ptolemy (the ancient Greeks, Egyptians and Babylonians who created these older constellations weren't familiar with the southern sky, and so other constellations were added in more modern times by European navigators as they traversed the Southern Hemisphere).

Hydra is also the largest and longest constellation in the night sky, spanning about 90 degrees (or about half the distance between opposite horizons). Its enormous size means that Hydra should be easy to spot in the night sky, but in fact it can easily blend into the background of fainter stars, as it contains only one noticeably bright star that's easily visible from the light-polluted cities where most of us live. That star, called Alphard, derives its name from Arabic and means, appropriately enough, "the solitary one".

Although many of the constellations in the night sky bear little or no resemblance to the figures they portray, you don't have to stretch your imagination far to understand how ancient people looking up at the heavens might have seen the long, twisting curve of stars with two 'eyes' and 'nostrils' at the top and named it Hydra, meaning "water serpent".

According to one myth, the Hydra was a monster with many heads that Hercules was sent to kill. As he cut off each of the creature's heads, two more grew back in their place. Hercules finally defeated the water serpent by burning the stumps of its severed necks and burying the final immortal head of the creature under a rock!

There are more than a dozen catalogued stars that make up Hydra the water serpent, but only two others, in addition to Alphard, have proper names: Minhar al Shuja ("the snake's nose") and Ukdah ("the knot").

The best time to see Hydra here in Canada is in the spring, when its full length is visible low in the southern sky just after sunset. The constellation moves westward until the end of June, when it begins to disappear below the horizon at dusk.

So remember, the next time you're standing on the front porch after dark with your sweetheart in your arms, you can look up at a beautiful night sky and point out the long, twisting figure of the terrible and hideous monster Hydra. No, wait...that doesn't work. Better stick to heroic Perseus and the beautiful maiden he rescued, Andromeda...

Learn More!


The Mythology of Constellations:

Thanks to Suzanne Taylor for her expertise on this subject. Suzanne holds a bachelor's degree in astrophysics from the University of Toronto and recently began a Masters of Journalism program at the University of Western Ontario, where she hopes to be able to put her sharp tongue and superior wit to use. In addition to astronomy and writing, she enjoys photography, travel, and spending time with parrots.


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