One thing's for sure. Cepheus (SEE-fee-us) has cold feet. Just look at how the original creators of the constellation pointed his toes toward Polaris and the north celestial pole. That's not all the mythical King of Ethiopia had to deal with in the day. He was married to Queen Cassiopeia, who was spectacularly vain. Always boasting of her beauty, she angered the god Poseidon to the point where he sent a sea monster named Cetus to pillage the Ethiopian coast.

The Oracle of Ammon instructed the couple to chain their daughter Andromeda to a rock as a sacrifice to the monster to appease Poseidon. At that point, Perseus the Hero got wind of the news. He came to rescue her and vanquish the beast on the promise of receiving Andromeda's hand in marriage. The king and queen agreed, but the wedding got off to a bit of a rocky start.

Cepheus and Cassiopeia pair up on the opposite of the North Star from the Big Dipper. They appear low in the northeastern sky at nightfall and gradually rise higher throughout the night. (Stellarium)
Cepheus and Cassiopeia pair up on the opposite of the North Star from the Big Dipper. They appear low in the northeastern sky at nightfall and gradually rise higher throughout the night. (Stellarium)

Andromeda had already been promised to Phineas, brother of Cepheus (bad idea). The night of the wedding, Phineas and friends crashed the party. After a pitched sword battle that saw Perseus turn the attackers into stone by showing them the head of the Gorgon Medusa, they were wed. Meanwhile, anticipating a bloody mess at Phineas' arrival, Cepheus quietly slipped out the back door grumbling about his lousy luck.

Cepheus is a five-sided figure shaped like an old army pup tent. Its brightest star, Alderamin, shines as bright as the stars in the Big Dipper. Errai hosts an extrasolar planet, while Delta Cephei pulsates like a slow-beating heart. (Stellarium)
Cepheus is a five-sided figure shaped like an old army pup tent. Its brightest star, Alderamin, shines as bright as the stars in the Big Dipper. Errai hosts an extrasolar planet, while Delta Cephei pulsates like a slow-beating heart. (Stellarium)

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Worse, while Cassiopeia received one of the most easily recognizable constellations in the sky, the King ended up with something resembling an army pup tent outlined by ho-hum stars. He must still be stewing up there. All the more reason to take the time and pay Cepheus a visit.

An old Dutch army tent from 1955 — see the resemblance? (Joost Bakker / CC BY-SA 2.0)
An old Dutch army tent from 1955 — see the resemblance? (Joost Bakker / CC BY-SA 2.0)

The 5-sided, modest constellation is first visible in late June and July in the northeastern sky as soon as it gets dark. As you'd expect, the King resides near the Queen. Find the W of Cassiopeia and you're just a fist or two from Cepheus. The 3rd magnitude star Errai, located at one corner of the tent, sits about two fists directly above Segin, the leftmost star in the W.

The planet Tadmor, formerly Gamma Cephei Ab, is larger and considerably more massive than Jupiter. It orbits Errai in Cepheus. (Open Exoplanet Catalog)
The planet Tadmor, formerly Gamma Cephei Ab, is larger and considerably more massive than Jupiter. It orbits Errai in Cepheus. (Open Exoplanet Catalog)

Although nondescript in appearance, the star, also known as Gamma Cephei (SEPH-ee-eye), has a lot going on. It's a close binary star located 44 light-years from Earth and orbited by the exoplanet Tadmor. The name is the ancient Semitic and modern Arabic name for the city Palmyra in Syria.

Tadmor is more than nine times as massive as Jupiter and orbits the pair of suns every 905 days at about the distance of Mars. Watching the suns go down at the planet would resemble the binary sunset depicted on the fictional planet Tatooine from Star Wars.

From Errai, work your way around the top of the tent to 3rd magnitude Alfirk, then to the constellation's brightest, or alpha, star, Alderamin. Connect in the two stars on the bottom side, and there you have it — the five sides of Cepheus.

One of my favorite stars in the figure, located just below the main outline, doesn't have a proper name. Called simply Delta Cephei, it's one of the most famous variable stars in the sky. Variable stars do exactly what their name says. Their light isn't steady like the sun's but changes in a cyclical way. Delta is a yellow giant that expands and contracts like a beating heart because it's unstable and can't settle down to a single size.

Like clockwork, the star completes one pulsation every 5.4 days, fading from magnitude 3.5 to 4.4 and back again. You can easily follow its "heartbeats" with the naked-eye from a reasonably dark location by comparing Delta's brightness to the stars Zeta (3.6) and Epsilon (4.2). The trio make a skinny triangle at the far corner of the tent.

When brightest, Delta's a little brighter than Zeta; when faintest it's slightly fainter than Epsilon. Give it a try. You'll be surprised at how easy it is to tell maximum apart from minimum brightness.

Astronomer Henrietta Leavitt worked as a "computer" at Harvard College Observatory measuring and cataloging stars on photographic plates. She discovered the relationship between the brightness of stars like Delta Cephei and their pulsation periods, called the period-luminosity relation. It revolutionized our understanding of the true size of the universe. (Courtesy of the AAVSO)
Astronomer Henrietta Leavitt worked as a "computer" at Harvard College Observatory measuring and cataloging stars on photographic plates. She discovered the relationship between the brightness of stars like Delta Cephei and their pulsation periods, called the period-luminosity relation. It revolutionized our understanding of the true size of the universe. (Courtesy of the AAVSO)

In 1912, American astronomer Henrietta Leavitt discovered that the brightness of a Cepheid variable (named for variables like Delta) is directly related to its pulsation period, which can range from about a day to 50 days.

If you determine distance of a nearby Cepheid of a certain period, you'll know its true brightness. Then if you see a Cepheid in a distant galaxy that has the same period, the difference between the apparent brightness of that star and the known star will yield its distance.

Cepheids are big and bright. That makes them the perfect tool to probe the distances to distant galaxies we otherwise couldn't measure by other methods. Thanks, Henrietta.

Little did Cepheus know he possessed a key that would expand the size of the known universe by leaps and bounds. A cure for a sour mood any day.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.