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February's Circle of Stars

by Charlie Jarman

We often feel that "amateur astronomy" must involve a major expedition to a rural area--or at least somewhere other than where we live--to enjoy the wonders of the sky. Most of us have experienced some degree of frustration during these outings, usually due to leaving an important part at home, bugs, or trying to learn how to use some accessory, that diminished the joy of observing. Now that I no longer own a telescope, I am beginning to realize that I never really learned to "observe" the stars and constellations. The search for those elusive deep sky objects never left time to see the "big picture" such as February's "Circle of Stars.

Facing East, an observer notices a "circle" of bright stars including (CCW from due east): Procyon in Canis Minor, Sirius in Canis Major, Rigel in Orion, Aldebaran in Taurus, Cappella in Auriga, and Castor and Pollux in Gemini. Here are some "jewels of knowledge" to help you enjoy naked-eye observing of these stars.

Procyon -- Procyon is the 8th brightest star in the sky, and is 11.3 light years away. Procyon has a luminosity of 6 times that of the sun and is about twice as large. The name "Procyon" has been in use since the days of ancient Greece, meaning "before the dog," an allusion to the fact that Procyon rises immediately preceding Sirius, and thus heralds the appearance of the great Dog Star. Procyon has several faint optical companions, the most interesting being a white dwarf called Procyon B which is the second closest of the white dwarfs to our solar system.

Sirius -- Sirius is the brightest of the fixed stars and is 9 times more brilliant than a standard first magnitude star. Sirius is an A1 type main star about 23 times the luminosity of the sun and about 1.8 times the diameter. Sirius is the 5th nearest star known, at a distance of 8.7 light years. Sirius has been described since ancient times as "The Sparkling One," "The Scorching One," "The Nile Star," and of course "The Dog Star." Sirius rises with the sun during the summer "Dog Days" of great heat. Sirius also has a white dwarf companion, Sirius B, which is the brightest and nearest of all the white dwarfs.

Rigel -- Rigel is the 7th brightest star at a distance of 900 light years. Rigel is a true supergiant with a surface temperature of 12,000 degrees Kelvin. Its energy output exceeds that of the Sun by a factor of many thousands, and the luminosity is 57,000 times that of the Sun. Rigel comes from Arabic meaning "left leg of the giant." Rigel has a companion that is visible in amateur telescopes, and the companion is itself a double, although beyond the detection of amateur equipment.

Aldebaran -- Aldebaran is the 13th brightest star with a diameter of 40 times that of the Sun and about 125 times the solar luminosity. Aldebaran is from Arabic meaning "the follower" or "the bright one of the follower" supposedly from the fact that the star follows the Pleiades across the sky. There have been many other names, and in various cultures it was connected with the spirits or gods of rain and the fertility of the earth. Aldebaran appears from earth to be a member of the Hyades star cluster, but the "membership" is accidental. It is about twice as close to us as the cluster. Aldebaran is one of the few stars of 1st magnitude that may be occulted by the Moon, and such events occur in "seasons" in which the star may be occulted repeatedly, month after month. In fact, since there is no lunar atmosphere, the occultation is startlingly abrupt and one of the most nearly instantaneous phenomena which the eye can observe.

Capella -- Capella is the 6th brightest star and is the nearest to the pole of all the first magnitude stars. From the USA, Capella is visible every night at some hour. Capella is 45 light years away and has a luminosity of 160 times that of the Sun. Capella is called the "Gopat Star" and is a multiple star system, although the components are not observable. A scale model of the system would show Capella A and B as two globes 13 and 7 inches in diameter and 10 feet apart; the components of Capella would then be 0.7 inches in diameter, 420 feet apart, and 21 miles from the main pair A and B!

Castor -- Castor is the 23rd brightest star with a luminosity of 36 times that of the Sun. Castor is 45 light years away and one of the finest double stars visible in amateur telescopes. There is a third visible star, although very faint, and each of the three stars is itself a binary, thus forming one of the most remarkable examples of a multiple star system.

Pollux -- Pollux is the 17th brightest star and 35 light years away. It has a luminosity of 35 suns and a diameter of 11 times that of the Sun. Pollux, although designated "Beta," is actually brighter than "Alpha" or Castor and it has been suggested that one of these stars has changed in luminosity in the last few centuries. Castor and Pollux form a prominent pair just 4.5 degrees apart and have since remote times suggested the concept of heavenly twins. In Greek mythology, they are the sons of Zeus and Leda; Roman writings describe them as the sons of Zeus and honored as guardians of the Eternal City. In the Greek world, Castor and Pollux were venerated by mariners, and were invoked for protection against storms and the perils of the seas. In the legend of the Argonauts we find them guiding and protecting the quest for the golden fleece. The electrical glow sometimes seen in a ship's rigging in stormy weather, and often called "St. Elmo's fire," was in classical times associated with the guiding spirit of the Twins.

FEBRUARY'S CIRCLE OF STARS
Face East around 8:00 p.m. and hold overhead

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