Stars over Sisters 8/03/2021

Gazing skyward on a dark, clear, warm summer evening in Central Oregon, observers will be rewarded by a multitude of celestial treasures. When it comes to peering into individual constellations, none of them have more to offer than Sagittarius, for there are spectacular sights of every sort. Even the center of our galaxy resides here.

Sagittarius, the celestial Archer, is the 15th largest constellation in our night sky. Because the sun visits here (in the dead of winter) on its annual journey across the celestial sphere, Sagittarius qualifies as one of the 12 zodiac constellations.

Locating this constellation is easy because of its distinctive shape, looking like an upright teapot. This perspective is enhanced by a bright patch of the Milky Way that lies just above the spout, making it appear as though steam is rising from the pot! The only downside to all this is that Sagittarius never gets higher than about 20 to 25 degrees above the southern horizon from our latitude.

The brightest star in Sagittarius is Kaus Australis, which is actually a binary star system, meaning that two stars orbit each other about a common center of gravity. This system has a magnitude of 1.85 and is approximately 143 light-years distant.

Sagittarius has a plethora of deep-sky objects, and no fewer than 15 of them are listed in Messier’s catalog. All are either dazzling star clusters, or some of the finest examples of brightly glowing clumps of interstellar gas.

Probably the most notable of these is M8, otherwise known as the Lagoon Nebula. This object is illuminated by ultraviolet radiation emitted from a cluster of newly formed stars within the gas cloud. Most backyard telescopes have no trouble revealing the milky-white nebula. This object is located approximately 5,200 light-years from Earth.

In Greek mythology, Sagittarius is usually depicted as a centaur: half human, half horse. Yet, there is some confusion surrounding the identity of the Archer. Some claim the centaur is Chiron, son of Philyra and Cronus, who was said to have changed himself into a horse to escape his jealous wife Rhea. However, Greek mathematician Eratosthenes suggests that the Archer was not a centaur, but the satyr Crotus, son of Pan, who is credited with the invention of archery.

The Perseids meteor shower will peak on the evening of August 11 through the early morning of August 12. During this time, Earth will cruise through the densest cloud of debris from Comet Swift-Tuttle. With a waxing crescent moon well out of the way in the early morning, observers may see as many as 80 to 100 meteors in an hour.

Both Venus and Mars are evening planets in Leo as the month opens. As August progresses, the speedier Venus pulls away from the sun to remain in the western sky for months to come. Mars, on the other hand, will not be able to hold off the advancing sun and will become lost in the brightening twilight.

Meanwhile, Mercury emerges from behind the sun after August 1 to become yet another evening planet. On August 18, about 30 minutes after sunset, Mars and Mercury will be separated by less than 10 minutes of arc.

Our solar system’s two largest gas giants join the evening parade this month: Saturn on August 2, Jupiter on August 19.

Dark evening skies will prevail during the first third of the month. Thereafter, the moon will become more illuminated until the Full Sturgeon Moon arrives on August 22.

This month’s dark-sky awareness tip to help fight light pollution here in Sisters is this: Use your outdoor lights only when needed. Consider putting them on a timer that will turn them off after a certain hour, or on a motion sensor that switches them on only when someone is present.