Stars over Sisters

Gaze skyward after nightfall in July and you will see a celestial crown.

Corona Borealis (Latin for "the Northern Crown") is a constellation that consists of seven stars arranged in a semicircle. It is bordered by Boötes to the west, Hercules to the east and Serpens Caput to the south. From our latitude here in Central Oregon, it will appear nearly overhead at about 9 p.m.

In Greek mythology, Corona Borealis represented a crown that was given by Dionysus (god of the grape harvest) to Ariadne, daughter of Minos of Crete. When she wore the crown to her wedding, where she married Dionysus, he placed her crown in the heavens to commemorate the wedding. To the Arabs the constellation was known as "the bowl of the poor people" because the stars form an unsymmetrical pattern.

There are a couple of interesting double stars in Corona Borealis. One of them is Nu Coronae Borealis, which consists of a red-hued giant star and an orange companion, both located about 550 light-years from Earth. Since the two stars have different radial velocities, it is assumed they are unrelated and only appear close together because of a chance alignment. The other double, Sigma Coronae Borealis, is a true binary system, as the two stars revolve about a common center of gravity.

Both stars are yellow, and the pair is located just 71 light-years from Earth.

Corona Borealis is nearly devoid of deep-sky objects. A notable exception is Abell 2065, a highly concentrated cluster of galaxies. The cluster is comprised of over 400 galaxies and is located more than a billion light-years from Earth.

Mercury will be between the earth and the sun (called inferior conjunction) on July 9, making the planet unobservable for most of the month. Venus moves from Cancer into Leo during July and can be seen low in the west after sunset. On the evenings of July 21 and 22, Venus and the bright star Regulus will be separated by just over one degree in the sky.

Mars begins the month in Taurus and then moves into Gemini to join Jupiter by month's end. The two planets will be less than a degree apart on July 22. Look for them low in the east about an hour before sunrise.

Saturn is still well-placed for observation, appearing nearly due south at dusk. The moon is waning as the month begins and completely disappears from the night sky on July 8, when the lunar phase becomes new. From here the moon slowly waxes (becomes more illuminated), reaching first-quarter on July 15 and full on July 22. As the moon continues in its orbit around the earth it once again dims, becoming third-quarter on July 29.

If you want help locating the Northern Crown, or other constellations of summer, consider attending the next Stars over Sisters star-watch to be held on Saturday, July 27, at Sisters Park & Recreation District's Coffield Center. The pre-star-watch presentation begins at 9 p.m. Afterward, all are invited to congregate on the Sisters High School soccer field, where telescopes will be set up for your viewing pleasure.