Many of the bright stars in the night sky are associated with a particular season — the time of year when they’re best seen 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, it’s been blazing across the evening sky since May. The orange star is quite low in the south-southwest at nightfall. Tonight, it’s almost directly below the Moon.

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 about 26,000 years to complete one full wobble, so it takes about a quarter of that — 6500 years — for a star to move 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 the Moon tonight. They’ll drop from view in late evening. But they’ll be back tomorrow night, with Antares a good bit farther to the right of the Moon.
 

Script by Damond Benningfield

Support McDonald Observatory