In 2007, a faint star in the constellation Bootes the Herdsman made astronomical history. An international team of astronomers, led by Jean-Francis Donati and Claire Montau of France, caught the star Tau Bootis flipping its north and south magnetic poles. These astronomers had been mapping the magnetic fields of stars. It was the first time a magnetic reversal had been observed on any star other than our sun.
Astronomers intently watched Tau Bootis for more magnetic turnovers, and it appears this star undergoes magnetic reversals in periods of about two years. They’re hoping Tau Bootis will enable them to understand how magnetic engines drive stars, including our sun. Also, Tau Bootis harbors a planet that’s several times the mass of Jupiter and has an orbital period of only three and one-third days. Hopefully, this star can shed some light on the relationship between stellar magnetic cycles and planetary climate.
Tau Bootis is faintly visible in a dark country sky. Look eastward this evening for the blazing yellow-orange star Arcturus, the brightest in your eastern sky. To verify that you’re looking at Arcturus, look for the Big Dipper up high in your northern sky. Follow the arc of the Big Dipper handle to Arcturus. Extend the arc even farther to find the red planet Mars, which is even brighter than Arcturus.
You’ll need a dark country sky and a moon-free night to see Tau Bootis with the unaided eye. This star is nearly 70 times fainter than Arcturus. On spring evenings, the star Muphrid shines to the upper right of Arcturus, and Tau Bootis lodges to the upper right of Muphrid.