The Really Round Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. The sun rotates every 28 days, and because it doesn't have a solid surface, it should be slightly flattened. This tiny flattening has been studied with many instruments for almost 50 years to learn about the sun's rotation, especially the rotation below its surface, which we can't see directly. Jeff Kuhn and Isabelle Scholl (Institute for Astronomy, University of Hawaii at Manoa) and others have used the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory satellite to find how astonishingly round the sun really is.
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