Stars over Sisters

Gemini is the featured constellation for the month of February in this edition of Stars over Sisters. This grouping of stars depicts a pair of celestial twins and is located between Auriga, Taurus and Orion to the west, Monoceros and Canis Minor to the south, and Cancer to the east.

Gemini ranks thirtieth in size among all the constellations and was first catalogued by Greek astronomer Ptolemy in the second century. Gemini is one of the 12 zodiac constellations. The zodiac is a band of constellations that lies on the ecliptic where the sun, moon and primary planets are always found. One of the interesting aspects about the constellation are the many stories found in Greek mythology.

Gemini represents the twins Castor and Polydeuces, sons of their mother, Spartan Queen Leda. Polydeuces was fathered by the god Zeus, but Castor’s father was Tyndareus, the mortal king of Sparta. The two boys grew up together and became very close. Castor became an excellent horseman and proficient at fencing while Polydeuces was famed for his boxing skills.

As adults the two were part of the Argonauts’ expedition to recover the Golden Fleece. However, the brothers eventually clashed with Idas and Lynceus, who were also twins and former Argonauts, over two women, Phoebe and Hilaira. A fight ensued and Lynceus slew Castor with a sword, and just when Idas was about to attack Polydeuces, Zeus intervened with a thunderbolt, saving his son. Polydeuces was grief-stricken and asked Zeus to share his immortality with his dead brother. The god obliged and placed them both in the sky where they remain inseparable as the constellation Gemini.

The two brightest stars in Gemini are Pollux (representing Polydeuces) and Castor, denoting the heads of the twins. Castor is a well-known double star to amateur astronomers, but there are actually six stars in this system that are so close together that spectroscopic analysis is required to detect their presence. Castor lies at a distance of 51 light-years. Pollux, brighter than Castor, has twice the Sun’s mass and about nine times the solar radius. An exoplanet was confirmed to be orbiting the star in June 2006. Called Pollux b, it has a mass at least 2.3 times that of Jupiter. Pollux is 34 light-years away.

Gemini contains two exceptionally fine deep-sky objects. The first is M35, one of the best examples of an open star cluster. It consists of several hundred stars arranged in a nearly circular pattern, with very little concentration near the center. Nineteenth century English astronomer William Lassell had this to say about M35: “a marvelously striking object. No one can see it for the first time without an exclamation.” The object is found at the foot of Castor and lies at a distance of 2,800 light-years.

Gemini’s second deep-sky object worthy of note is planetary nebula NGC 2392, often referred to as the Eskimo Nebula. It consists of the glowing remains of a dying sun-like star that is blowing off its outer atmosphere into space. Recent photographs of this object are striking because the nebula resembles a face surrounded by a fur parka. NGC 2392 is about 2,870 light-years from our solar system.

Of the five visible planets in our solar system, only the two innermost worlds are visible in the evening hours.

On February 10, tiny Mercury stands 11 degrees above the southwestern horizon half an hour after sunset. This will be the best time to see the planet all year. Venus is there too, of course, as it is the brightest object in the sky after the sun and moon.

The three remaining superior planets are all morning objects. Mars rises first just before 4 a.m. local time at the beginning of the month. Jupiter pops up around 90 minutes before the sun, followed by Saturn 40 minutes later. By the end of February all three planets rise before twilight begins.

Let’s not forget about the earth’s closest natural body in space. Our moon will become the Full Snow Moon on the 8th, last quarter on February 15 and new moon on February 23. Additionally, the moon will be closest to the earth (perigee) on February 10 at 223,980 miles and farthest away (apogee) on February 26 at 252,450 miles.

If you want to learn more about astronomy, consider a visit to the Oregon Observatory at Sunriver. During February the facility is open for solar viewing Friday through Sunday from 11 a.m. to 2 p.m., and Wednesday and Saturday nights 7 to 9 p.m. The observatory has the largest collection of public ­viewing telescopes in the country.