Stars over Sisters

The summertime constellation of Ophiuchus was among the first star patterns to be cataloged by Greek astronomer Claudius Ptolemy in the Second Century. The name means "Serpent Bearer" in Greek, though it is sometimes referred to by its Latin name, Serpentarius. Ophiuchus is usually depicted in star charts as a man holding a snake, namely Serpens.

Ophiuchus is the eleventh largest constellation by area on the celestial sphere but contains no stars brighter than second magnitude. Although a portion of the ecliptic crosses into the southern portion of the constellation, it is not recognized as a zodiacal constellation. It is best seen near the meridian in the southern sky at about 10 p.m. during July. Look northeast from the bright star Antares in Scorpius.

The brightest star in Ophiuchus is Rasalhague, Arabic for "The Head of the Serpent Charmer." It is a binary star system located about 49 light-years from the earth. The primary component is a bluish-white subgiant star that is 2.4 times more massive and shines 25 times brighter than our sun. The mass of the secondary component is only 0.85 solar masses. Light from the two stellar components combine to cause Rasalhague to glow at second magnitude.

Perhaps the most significant star in Ophiuchus is Barnard's Runaway Star. In 1961 American astronomer Edward Emerson Barnard measured the proper motion of this dim red dwarf star and found it to be moving through space at the rate of 10.3 arcseconds per year, highest known for any star. It is the closest star to the sun, after the Alpha Centauri trio.

Because Ophiuchus is a relatively large constellation that lies close to the Milky Way, many exceptionally fine deep sky objects are located here. The assortment is impressive and includes diffuse nebulae, dark nebulae, planetary nebulae, and open star clusters. But most of these objects are globular star clusters, some as beautiful as found anywhere else in the sky.

One of these globular clusters is M19, located about 7 degrees due east of the bright, reddish star Antares. It was discovered by Charles Messier in 1764 and added to his catalogue of comet-like objects that same year. It is one of the most oblate known globulars, having a distinctly elongated shape in the north-south direction. This cluster contains an estimated mass more than a million times greater than the sun. It is thought to be approximately 11.9 billion years old and lies at a distance of 28,700 light-years.

Ophiuchus is most frequently associated with the Greek mythical figure of Asclepius, son of the god Apollo, who was said to be able to bring people back to life with his healing powers. Asclepius learned how to do this after seeing one snake bringing healing herbs to another. This happened when Glaucus, the son of King Minos of Crete, fell into a jar of honey and drowned. Asclepius saw a snake slithering toward his body and did away with it. Then another snake came along and placed an herb on the first one, which miraculously brought the first snake back to life. Asclepius saw this, took the same herb, and placed it on Glaucus' body. The king's son was miraculously resurrected.

The solar system's two inferior planets, Mercury and Venus, occupy the evening sky this month. On July 7 they are joined by a thin waxing crescent moon to provide a picturesque setting just above the western horizon. Mercury continues to hang around until reaching its greatest eastern elongation on July 22, after which it will slowly sink below the horizon. Venus can be seen throughout the entire month.

The three remaining visible planets are morning objects. Saturn rises at midnight, Mars arrives on the scene just after 2 a.m., and Jupiter joins the party a short time later at 3:30 a.m.

To help fight the growing problem of light pollution, please remember to keep your outdoor lights targeted downward and shielded. Doing so will help you see all these beautiful events!