Crazy Capricornus — Boat, Goat And Smile In The Sky


Mars is smack dab in the middle of the constellation Capricornus the Sea Goat in mid-October. Key stars are labeled with Greek letters . Generally, a constellation’s Alpha (α) star is the brightest, followed by Beta (β) and so on up to Omega (ω). However, with Capricornus, Delta is brightest and Omega is not the faintest! Theta (θ) Capricorni currently lies due north of Mars. Stellarium

Some people see a paper boat, others a goat, some a sloppy triangle and others the mischievous grin of the Cheshire Cat. Whatever we behold in the curious constellation of Capricornus, I was just happy for clear skies to see it last night. Two weeks of cloudy nights have been too much for this star-craved human to bear.

The Cheshire Cat from Lewis Carroll’s “Alice in Wonderland.” Remember, the last thing to remain as the cat disappeared was its famous grin. John Tenniel 1865

With the return of the stars, I noticed that Mars has been on the move east and now shines from the center of Capricornus. The Red Planet hasn’t lost its visual magnetism despite having faded to magnitude –1.0 in part because it has no competition — Capricornus is one of the fainter constellations with no star brighter than third magnitude. Mars still bests Canopus, the second brightest star, and stands only half a magnitude behind the brightest star Sirius.

Mars won’t be locked inside its Capricornus cage for very long. Each passing night it edges eastward (to the left from the northern hemisphere) and further north as it orbits the sun. If you watch closely and compare the planet’s night-by-night position with stars in the figure, you can actually see Mars move in 24 hours. Don’t wait too long — by Halloween, the planet will have fled

The Greek alphabet.

But first you have to find Capricornus, and it’s not a bright constellation. Good thing Mars is there. Starting at the planet, look a little more than one outstretched fist to the upper right to find a pair of 3rd magnitude stars, Alpha and Beta Capricorni. Now, return to Mars and look a little more than a fist to the upper left to spot Delta Cap (short for Capricorni). Delta is the brightest star in the constellation by a hair. Second brightest is Beta and third brightest, Alpha.

Usually, a constellation’s brightest star is Alpha, followed by Beta then Gamma and so on. Usually. But sometimes a star’s position in the sky is more important than splitting hairs about its brightness. To the ancients, stars had other important qualities besides just brightness. Position mattered, too.

That’s the case with Alpha Cap, which got the designation because it’s the brightest, westernmost star in the figure. While it sets before the others, it also is the first to rise, lending it notoriety.

Beta really is Capricornus’ second brightest star, and having it right next to Alpha makes for a convenient, easy-to-remember Alpha-Beta pairing.

The lazy triangle of Capricornus represents a “sea goat” to those with a good imagination and dark skies. Urania’s Mirror/Sidney Hall

Astronomer James Kaler once wrote: “Omega stars,” those named with the last letter of the Greek alphabet, get little respect.” That may be true but Capricornus’ Omega takes a prominent position in the constellation because it marks the bottom apex of a triangle formed by Delta and the Alpha-Beta duo. If you can find the basic triangular outline, with or without the fainter “filler” stars, congratulations!

Most people, if they look closely on a clear night, can split Alpha into two stars with the naked eye. Binoculars make it easy work. The two Alpha stars form an “optical double,” two unrelated stars seen along the same line of sight.  Alpha-1, the fainter, is 690 light years from Earth and Alpha-2, 109 light years. Despite appearances, Alpha-1 is a supergiant star 930 times brighter than the sun. Alpha-2 is likewise a giant star 43 times more luminous than the sun. Alpha is also known by its proper name Algedi and Beta as Dabih. Stellarium with additions by the author

Capricornus is one of the most ancient constellations and represents a unique figure among the 88 groups, a creature that’s half goat and half fish. The myth comes to us from Mesopotamia from 5,000 years ago. Then, the figure represented the boat of the god Enki, the Sumerian god of water, wisdom and creation. Enki means “Lord of the Earth” and his symbols were the fish and the goat, both representations of fertility and identified with the constellation to this day.

Because all stars except the sun are so far away, their light takes from several to tens of thousands of years to reach our eyes. To look at a star is to look back in time. Capricornus telescopes time, taking us back across dozens of centuries to reconnect with one of the great cultures of the ancient world.