The sun is the most perfectly round natural object known in the universe. As a spinning ball of gas, astronomers always expected it to bulge slightly at its equator, but it doesn’t bulge much at all. It is 1.4 million kilometres across, but the difference between its diameter at the equator and between the poles is only 10 kilometres. Scaled to the size of a beachball, that difference is less than the width of a human hair.
The results, reported in the journal Science, are the culmination of 50 years of efforts to precisely measure the sun, which have been hampered by the blurring effects of the Earth’s atmosphere. “Finally, from space, we have it nailed,” says Kuhn.
They used instruments on Nasa’s Solar Dynamics Observatory, though these were not precise enough to make the observations directly. The satellite had to be rotated to take images of the sun at all orientations so that tiny imperfections in the spacecraft’s instruments could be averaged out.
The observations are key to learning about the sun’s interior, which rotates at different speeds like traffic moving at different speeds on a motorway. This speed distribution can be inferred from measurements of the star’s shape and the way that it wobbles. The new measurement indicates that the outer layers are moving more slowly than expected: Kuhn suggests that turbulence under the surface is probably the cause.
Picture Credit : Google