A group of astronomers led by the University of Hawaii's Dr. Jeff Kuhn has made the above finding.
"This constancy is baffling, given the violence of the changes we see every day on the Sun's surface and the fluctuations that take place over an 11-year solar cycle," said Kuhn.
The work is part of worldwide efforts to understand the influence of the Sun on Earth's climate.
"We can't predict the climate on Earth until we understand these changes on the Sun," said Kuhn.
The researchers used NASA's long-lived Solar and Heliospheric Observatory (SOHO) satellite to monitor the Sun's diameter, and they will soon repeat the experiment with much greater accuracy using NASA's new Solar Dynamics Observatory (SDO), which was launched on February 11.
Kuhn said that the ultimate solution to this puzzle would depend on probing the smallest observable scales of the solar surface using the Advanced Technology Solar Telescope (ATST), which is scheduled for completion on Haleakala in 2017.
"To be able to predict what the Sun will do, we need both the big picture and the details. Just as powerful hurricanes on Earth start as a gentle breeze, the analogs of terrestrial storms on he Sun start as small kinks in the Sun's magnetic field," said Kuhn. (ANI)