Stars over Sisters

At 8:50 p.m. on Thursday, March 19, the sun will lie directly above the equator and the spring season will officially begin smiling upon Sisters and all of the Northern Hemisphere. Here on the ground, it can be easy to overlook the astronomical clockwork responsible for the change in season, and how it affects our perception of the space around us. However, the motion of our fragile planet whirling through space allows for the way we see the night sky to be constantly changing. In addition to the promise of warmer weather, the arrival of the new season will bring us a fresh perspective of the heavens, and a reminder of the enormity and beauty of the universe we inhabit.

Ascending into the northeastern sky during March evenings is one of the most easily recognized spring-time stellar groupings in the northern celestial sphere. It is, of course, the Big Dipper, which is part of the constellation of Ursa Major, a Latin name meaning “the great bear.”

The satisfaction that comes from finding the stars that define the outline of the bear can often be enhanced by exploring some of the many tales invented to explain why we should see this shape.

One such story comes from the ancient Greeks.

In the legend, Zeus, king of the gods, has a son, named Arcas, with the beautiful nymph Callisto as a result of one of his many affairs.

Hera, the wife of Zeus, is understandably annoyed by this, and, naturally, turns his lover into a bear, to work out some of that anger.

Callisto wanders the forest for years, and one day crosses paths with her son, now a grown young man, while he is hunting.

But Arcas doesn’t recognize her (probably because she is now a bear), and prepares to attack, out of fear.

Zeus sees all of this from Olympus and does not want his son to kill Callisto.

The king of the gods probably thinks that the situation is already complicated enough, without his illegitimate son unknowingly murdering his own mother.

Acting quickly, he causes a great wind to carry them up to the sky where they are now protected as constellations: Callisto as Ursa Major, and her son, Arcas, as Boötes, the Herdsman.

There is a plethora of magnificent deep sky objects that lie within the borders of Ursa Major, most of them galaxies. One of the more photogenic of these is M101, a gorgeous face-on galaxy with well-developed arms that spiral outward from its central region. Sometimes referred to as the Pinwheel Galaxy, this object is located at a distance of about 21-million light-years.

Spring is the best time of the year to look for a faint glow on the western horizon once dusk has passed. It is known as the zodiacal light and is caused by sunlight reflected by dust particles and rocky debris that orbit in the inner solar system. Now is the ideal time of the year to see the zodiacal light because the ecliptic — the path of the sun, moon and planets across the sky — is highly inclined to the western horizon in the evening. Autumn is also a good time to see the zodiacal light, only this time appearing just before dawn on the eastern horizon.

Venus continues to lead the planetary parade, shining brightly in the western sky. It spends most of March in Aries, then crosses into Taurus at the end of the month. Lined up across the morning sky are Mars, Jupiter and Saturn, from west to east, respectively. But Mars is traveling eastward much faster than the two gas giants and will catch up to Jupiter on March 20.

By mid-month Mercury makes an appearance in the morning sky, reaching greatest western elongation (greatest angular distance from the sun) on March 23, but it will stay low in the sky because the ecliptic makes a shallow angle with the eastern horizon this time of year.