Stars over Sisters

As the year 2018 advances into its second month, celestial treasures await discovery by curious observers. Chief among them is the famous Pleiades star cluster, which is near the meridian at nightfall in February.

Located in the constellation of Taurus, this group of stars marks the Bull's shoulder. The Pleiades cluster is known by many names, such as M45, the Seven Sisters and Subaru, Japanese for Pleiades. In fact, the Subaru car company uses the cluster as its logo, but featuring only six of the seven stars because tradition says that one of the "sisters" is invisible.

The Pleiades is rich in Greek mythology. The Seven Sisters were daughters of the titan Atlas and the sea-nymph Pleione, and their names were Maia, Electro, Alcyone, Taygete, Asterope, Celaeno and Merope.

The story tells of how Orion the Hunter took a liking to Pleione and her seven daughters and began to chase them round when Atlas was tasked with holding up the heavens on his shoulders by Zeus. This frightened the women to the point that Zeus eventually transformed all of the sisters into white pigeons that flew up into the night sky and turned into a cluster of seven stars, known as the Pleiades. The constellation of Orion is said to still chase them across the night sky.

The cluster is made up of extremely luminous middle-aged, hot B-type stars that have formed within the last 100 million years. Astronomers say the faint reflection nebulosity around the brightest stars was once thought to be leftover material from the formation of the cluster, but is now known to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing. M45 is one of the nearest star clusters to the earth, lying at a distance of just 445 light-years.

By the end of February Mercury and Venus, the solar system's only two inferior planets (at least as viewed from the earth), can be glimpsed very low on the western horizon just after sunset. Using a pair of binoculars in this endeavor will increase one's likelihood of success.

But the best planetary display is in the morning sky. Jupiter rises before 2 a.m. local time at the beginning of the month; just before midnight by month's end, and spends the entire time in the constellation of Libra.

On February 1, Mars is about 12 degrees to the lower left of Jupiter in the constellation of Scorpius. Throughout the month, however, the Red Planet races eastward among the stars to a position in Ophiuchus, a full 27 degrees from Jupiter on February 28. An interesting exercise during this time is to compare the brightness and color of Mars with the nearby red-giant star Antares, known as the rival of Mars.

Saturn doesn't rise until almost 5 a.m. at the beginning of the month; two hours earlier as the month expires.

Because of last month's Blue Moon on January 31, the month of February will not be cursed with a dark-sky-spoiling full moon. The lunar phase wanes to last quarter on February 7 before going dark on February 15. From here a brightening moon will appear half lit at first quarter on February 23.