Astronomers have sought for centuries to see if and how our backyard star's roundness changes. That's because even slight changes in the sun's shape can alter its brightness and, as a result, influence weather and climate on Earth.

But getting a read on the sun's shape from the ground is hard, due to turbulent air that refracts light and generates inaccurate measurements.

Spacecraft eventually worked around that issue, yet poor image resolution became the next hurdle: Without a crisp view of the rotating sun, it's difficult to improve existing measurements.

(See "Sun Is Moving Slower Than Thought.")

"The sun is very, very round, so it's difficult to measure any deviations in that roundness," said study leader Jeffrey Kuhn, a solar researcher and physicist at the University of Hawaii.

"It's only been in the last few years that we've been able to make decent shape observations."

Those advances are due in part to NASA's Solar Dynamics Observatory (SDO), which launched in February 2010 and has some of the best cameras fixed on the sun. So when Kuhn earned some time controlling the spacecraft, he got to work.