The Heart of the Monster

Those who look forward to seeking out goblins, demons, monsters, and other scary critters during this spooky season need look no further than the skyscape that is displayed during these long nights. Last week, my early morning stargazing* taught me a new monstrous constellation.

I'd been scanning the dark gulf between Procyon and Regulus, in hopes of figuring out Cancer, the Crab. A very faint constellation with no star brighter than 4th magnitude, Cancer isn't easily seen this close to "civilization," or with a lightening dawn to compound the challenge. I got a bonus—even spookier than the pale Crab was the critter below.

My eye is always captured, it seems, by the red or orange stars, and just below Cancer, alone in the field, was Alphard, the Solitary One. Alphard, a mid-2nd magnitude star, is also known as Cor Hydrae, the heart of the Hydra, a vast sea monster that stretches across the otherwise quiet space between Cancer and Virgo, ending far east below Spica. The brightest star in a dim constellation, Alphard is more impressive than it looks from here: 175 light-years away, 40 times the Sun's diameter, and burning 400 times brighter. Alphard is an orange giant nearing the end of its life.


Although most of the Hydra was invisible, Spica itself is easy to find, being south of Arcturus, another of my favorite red stars, who was just rising. In fact, Arcturus and Spica were about the only stars visible in that lightening part of the sky. (And, of course, we get to Arcturus by "arcing" along the handle of the Big Dipper and following the arc on to Spica.)

Harry Potter fans might prefer to think of Hydra as the giant and evil basilisk; the resemblance is certainly compelling for a latter-day mythology. Other constellations have been translated to modern times (still looking for that link), so why not Hydra? As the largest constellation, the Water Serpent stretches one-quarter of the way around the sky.

* Please note: Early morning stargazing throws me off schedule with more "normal" evening observers, who should look for the Hydra crossing southern skies February through April.

Hydra may be the largest, but it is not the only, monster up there. There is, to name one example, another sea monster, Cetus, off on the other side of the sky just below the raging bull, Taurus. The story of that monster is well displayed in Watcher's most-thorough post on Andromeda (and almost everything else), which takes in the mythology of Perseus and Cetus and the entire cast of characters in this part of the sky. Here's Perseus as it appears in the east on a fall evening.

Speaking of Perseus (nice seque, eh?), another demon appears in that constellation— as Watcher will explain, the hero Perseus is carrying the severed head of Medusa the Gorgon, she of the serpentine coif. The star Algol represents Medusa's head or eye, and glares in our direction with great malevolence. The name Algol, in fact, is from Arabic for "the ghoul" or demon, and she is an appropriate visitor for the Halloween season.

Algol's gaze, like Medusa's, is considered unlucky. The system is actually a double star, with a bright blue primary and a yellow secondary. As the two stars circle, one eclipses the other every three days, causing the brightness we see to dip from magnitude 2.1 to about 3.4. This eerie blinking of the demon's eye gives the star its unsavory reputation, although it happens so quickly I've yet to catch it in action (or, likely, my ability to judge its relative brightness is underdeveloped). No matter, it gives me something to watch for...