Like a bear that spends part of its time in hibernation, the Sun goes through cycles of more and less activity. It’s at its most active every 11 years, when it produces large numbers of magnetic storms — dark sunspots and bright flares. And it’s least active about half way between peaks. It’s in one of those quiet cycles right now.

Other stars go through their own magnetic cycles. Two of the best known are Alpha Centauri A and B. They’re just four-and-a-third light-years from Earth. Only their smaller companion, Proxima Centauri, is closer to us.

Star A is a bit bigger and heavier than the Sun. Star B is a little smaller and lighter than the Sun.

X-ray telescopes in space have been watching the system for years. Over the last decade, in fact, Chandra X-Ray Observatory has looked at the system twice a year. Those observations have helped show that both stars have their own magnetic cycles. Star A’s cycle appears to last about 19 years, while B’s is only about eight years.

Chandra also found that any planets around the stars receive relatively low doses of X-rays — good news for any life at Alpha Centauri.

The system is in the constellation Centaurus, which is wheeling quite low across the southern evening sky. To the eye alone, its stars look like a single pinpoint — the third brightest in the night sky. But the system is quite far south. So from the U.S., it’s visible only from Hawaii and far-southern Texas and Florida.

Script by Damond Benningfield