By Ron Cowen
When the moon eclipses the sun, it unmasks a glorious halo–the glowing gases in the sun’s outer atmosphere, or corona. Six decades ago, observations in visible light revealed that the corona has a temperature greater than 1 million kelvins, making it hundreds of times hotter than the sun’s surface.
Now, for the first time, astronomers using a ground-based telescope have observed near-ultraviolet light from another star’s corona. The achievement demonstrates an easy way to examine the outer atmosphere of stars, assert Jürgen H.M.M. Schmitt and Rainer Wichmann of the University of Hamburg in the Aug. 2 Nature. Previously, astronomers could view coronas of stars beyond the sun only at X-ray wavelengths, a task that requires telescopes on spacecraft.