|The largest of all 88 constellations is called Hydra, the water snake. It's huge. It forms a line that wraps around the sky all the way from the stars of Cancer to those of Libra. If you go out and see the toothy business end just starting to rise in the east, you will wait about six hours for its tail to clear the horizon.
Hydra is a girl snake and she has little cousin down south. He's a boy snake named Hydrus. The boy is new in town but Hydra goes way back. Ptolemy included it in his collection about 2000 years ago, but it can be traced back at least to the ancient Babylonians. That's a long time ago. Remember Babylon was ancient history to Ptolemy.
Hydra is sometimes a multi-headed monster, or sometimes not, depending on which hero is telling the story. The most told story is the Greek version which is how Hercules had to fight Hydra while Cancer the Crab was pinching at Herc's ankles at the same time. Hercules and his favorite nephew killed the mighty multi-headed worm by chopping off the heads one by one and burning the bloodied necks so the heads couldn't grow back. One of the heads refused to die so Herc buried it under a rock. Then they all had a tasty dinner of boiled crab legs. The story of Hercules and Hydra has persisted through the ages because the challenge of battling multiple problems that grow back as fast as you can cut them off is something anyone in middle management can relate to.
Around the time of the autumn equinox the sun has dropped down near Hydra's head and thus reenacts the Herculean battle. Perhaps a better characterization is that Hercules represents the yearly battle that the sun has with the snake, since the sun's battles with Hydra predate the Greek stories. It seems like every culture on Earth has some version of a hero meeting a mighty reptile.
The battle doesn't goes well for the beloved hero. He fights bravely but he loses, and the dangerous reptile then rules the realm. The hero lies nearly motionless at the nadir of his tale. These are the cold, dark days of winter. But alas he awakens.
For the next forty days the hero rehabilitates. Even more, he spends this chapter being educated, preparing, elevating his capacity to make war on his enemy. The hero arises from the depths to once again meet the monster, this time on the spring equinox. Darkness is defeated in spectacular fashion. The crippled reptile is then cast down to the depths, exiled out of sight below the Earth. The longer, brighter days return. The victorious hero rises high above the realm bringing light, and life-giving energy to the world, which usually celebrates by grilling some kind of meat, maybe crab legs.
Alphard is the lonely bright star in Hydra. Its name mean "The Solitary One." It is extremely young compared to our sun but it is mature for its age. That's because it has about three times the mass of our sun and it has used all that extra weight to hurry along the stellar evolutionary process.
M83 is a nice face-on barred spiral galaxy in Hydra, also known as the Southern Pinwheel. It's only about 15 million light years away, which is practically next door in galactic terms. You can even see it with binoculars. Which of course means that critters living there can see our galaxy in binoculars as well.
Galaxies come in clusters and there is a doozy in this direction known as the Hydra Cluster. It has more than 150 galaxies packed in a box about 10 million light years wide. The Hydra Cluster is also thought to contain an extraordinary amount of dark matter, whatever that is. Anyway, the whole cluster is just a small part of the Hydra-Centaurus Supercluster which is a cluster of clusters of galaxies.
The Universe appears to be made out of shit-loads of superclusters that all overlap each other like soap bubbles. Our own bubble is called the Virgo Supercluster and it has about a hundred clusters of galaxies. But here's the latest news. Recent observations seem to indicate that the Hydra-Centaurus Supercluster and Virgo Supercluster are both just small parts of an even bigger supercluster known as the Laniakea Supercluster. And that mega-monster of 100,000 galaxies represents one tiny little speck of the universe.