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Faint star in Bootes makes history


Tonight for April 18, 2015

Tonight … a word about a faint star in the constellation Bootes the Herdsman that made astronomical history in the year 2007. In that year, an international team of astronomers, led by Jean-Francis Donati and Claire Montau of France, caught the star Tau Boötis 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 Boötis for more magnetic turnovers, and it appears this star undergoes magnetic reversals in periods of about two years. They’re hoping Tau Boötis will enable them to understand how magnetic engines drive stars, including our sun.

Also, Tau Boötis harbors a planet that’s several times the mass of Jupiter and has an orbital period of only three and one-third days. In 2014, astronomers found water vapor in this planet’s atmosphere. They’re hoping this star and its planet can shed some light on the relationship between stellar magnetic cycles and planetary climate.

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Tau Boötis is faintly visible in a dark country sky. Look eastward on these April evenings 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’s handle to Arcturus.

You’ll need a dark country sky and a moon-free night to see Tau Boötis with the unaided eye. This star is nearly 70 times fainter than Arcturus. On these northern spring evenings, the star Muphrid shines to the upper right of Arcturus, and Tau Boötis lodges to the upper right of Muphrid.

Bottom line: In 2007, a faint star in the constellation Bootes the Herdsman made astronomical history, when astronomers caught the star flipping its north and south magnetic poles. This post tells the story of that star, Tau Boötis, and also shows you how to find the star in the night sky.

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