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Constellation of the Month: Auriga, the Charioteer

February sees a pentagon-shaped constellation high in our northeastern sky with a bright first-magnitude star. The Charioteer, Auriga, always stays in the northern part of our sky, circling the north celestial pole every day. The bright star Capella marks the location of this constellation, even as it dips below the northwestern horizon early in the morning hours.

Click the image to enlarge the map.

Facing north and looking high in the northern sky, Auriga is already past the zenith on these cold February nights. (Remember that west is to the left when facing north.) The star above and to the left of Capella marked with the backwards "E" is Epsilon Aurigae, the giant eclipsing binary some 2,000 light years away. The triangle it is a part of is called "The Kids."

There are a number of mythological stories behind this distinctive constellation. Perhaps the most interesting is that of Myrtilus, the charioteer of King Oenomaus and a son of the god Hermes. This king had a great love of horses, having received a team of the fastest horses on Earth from the god Ares. He named his beautiful daughter Hippodameia, meaning the "horse tamer." King Oenomaus was also jealous of his daughter, and to keep her suitors from winning her hand, he insisted that each one race against the king and his lightning-fast team. This was not just a race for the princess, but a race to the death, for if the suitor lost, he was killed. Many a suitor lost his life seeking Hippodameia's hand.

Finally, Pelops, another son of Hermes, arrived to seek the hand of the princess. On seeing him, Hippodameia fell in love with Pelops. The gods also had had enough of King Oenomaus killing off young men, so the god Poseidon gave Pelops a golden chariot with winged golden horses. To insure a win, Hippodameia convinced her father's charioteer, Myrtilus, to tamper with the chariot. Myrtilus was secretly in love with Hippodameia and willingly did her bidding.

During the race, the wheels came off the king's chariot and he was dragged to his death, leaving Hippodameia free to marry Pelops. When Myrtilus protested, he was unceremoniously dumped into the sea to drown. But Hermes raised his son up and put him into the sky as Auriga.

Interestingly, Capella, the brightest star in Auriga, is identified with the Amaltheia, the goat that suckled Zeus when he was young. At some later point, Zeus accidentally broke off the goat's horn. This piece of horn, made magical by Zeus, would fill with whatever the possessor wanted. It was named Cornucopia, or "horn of plenty."

Southeast of Capella is a little isosceles triangle called "The Kids" (as in goats, not children). The northern star is called Almaaz, which is marked on star charts as Epsilon Aurigae. This star varies its brightness over a period of 27.1 years, from magnitude 3.0 to 3.8. This variable star is actually a quadruple star, but two of these stars go around each other in such a way that the one of them periodically blocks the light of the other as seen from the Earth. This is called an eclipsing binary and is not too uncommon. Nothing else about Epsilon is common, however.

The main star is a hot F0 star that has entered the supergiant phase, so large that it would stretch from one side of the Earth's orbit to the other–some 2,000 times bigger than our Sun. But as big as the star is, the object that goes between it and the Earth every 27 years is 20 times larger: a vast disc of dust and gas that orbits 2.7 billion miles from the central star. It takes two years for this eclipsing disc to pass in front of Epsilon. This will happen again from 2009 to 2011.

Near the middle of the eclipse, Epsilon brightens a little, so we know there is a doughnut hole in the middle of the disc. We are not sure what occupies the doughnut hole, but it is believed that it is a pair of giant class B stars orbiting tightly around each other as they make their slow orbit around Epsilon. One thing is certain: One day, Epsilon will collapse in a supernova explosion, but not anytime soon.


The Planets for February 2007

Venus pops out of the evening twilight as it starts to get dark. Shining brilliantly at magnitude -4.0, our Evening Star starts the month in Aquarius, moving quickly into Pisces. It then slides over the corner of Cetus and back into Pisces, where it ends the month. Venus is almost full, being almost 90 percent illuminated at mid-month. It is becoming less full every day as its 11.4 second-of-arc disc slowly shrinks.

Watch the Skies
(all times MST)

Feb. 1, 10:45 p.m.
Full Moon

Feb. 2, 4 p.m.
Saturn 0.9 degrees
south of the Moon

Feb. 7, 10 a.m.
Mercury farthest
from Sun (18 degrees).

Feb. 10, 2:51 a.m.
Last Quarter Moon

12 noon
Saturn at opposition

Feb. 17, 9:14 a.m.
New Moon

Feb. 24. 12:56 a.m.
First Quarter Moon

Mercury is also in Aquarius during February. Both it and Venus are moving eastward along the ecliptic. On Feb. 7, Mercury reaches its farthest point from the Sun; it will be magnitude -0.6, about seven degrees below and slightly right of Venus. The Messenger of the Gods then turns around and dashes back toward the Sun, disappearing into the evening twilight by mid-month.

Saturn is in opposition on Feb. 10 and is visible all night. The best time to observe the Ringed Planet is around midnight when it is highest in the sky. Still in western Leo, Saturn is magnitude -0.2 and its disc is 20.2 seconds-of-arc across, the biggest it will be all year. The rings are 45.8 second-of-arc across, tilted up 14.1 degrees with the southern face showing

The King of the Planets rises around 3 a.m. in the east-southeast. Staying in Ophiuchus all month, Jupiter is magnitude -2.0 and 35.1 seconds-of-arc across. It is best observed just before morning twilight begins.

Mars comes up two hours later, starting the month just northeast of the Teapot in Sagittarius. On Feb. 25, Mars moves into Capricornus. The Ruddy Planet is magnitude 1.3. Its disc is 4.3 seconds-of-arc across, slowly growing larger as it moves toward opposition in December. It is still too small to really observe, but as we progress through the year, it will be getting larger, so "keep watching the sky"!


An amateur astronomer for more than 35 years, Bert Stevens is co-director of Desert Moon Observatory in Las Cruces.


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