Many of the bright stars in the night sky are associated with a particular season — the time of year that they’re best viewed during the evening hours. For those of us in the United States, for example, the star Antares is one of the highlights of summer. In fact, after blazing across the evening sky since May, it’s just disappearing from view right now. The bright orange star is quite low in the southwest at nightfall. Tonight, it’s almost directly below the planet Venus, the “evening star.”
Antares won’t always highlight the skies of summer, though. In a few thousand years, it’ll become an autumn star. And a few thousand years after that it’ll move into winter skies, then spring, and finally back to summer.
The change is caused by an effect known as precession. The gravitational pull of the Sun and Moon cause Earth to wobble like a gyroscope that’s running down. As the planet wobbles, so does our view of the stars — they shift position relative to the seasons, so they rise and set later in the year.
It’s not noticeable over a human lifetime, though. It takes Earth 26,000 years to complete one full wobble, so it takes about a quarter of that — 6500 years — for a star to shift from one season to the next. So Antares will remain a summer star for a long time to come.
Again, look for Antares quite close to Venus tonight. Venus will move up and away from the bright star over the following nights as Antares drops toward the Sun — and out of sight.
Script by Damond Benningfield, Copyright 2013