Scientist studies sun's brightness cycles

FAIRFAX, Va., Jan. 24 (UPI) -- A U.S. physicist has determined the sun's brightness rises and falls about every 100,000 years -- the same period as between Earth's ice ages.

Robert Ehrlich of George Mason University devised a computer model that reflects the effect of temperature fluctuations in the sun's interior. According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. However, Ehrlich said slight variations should be possible.

Small instabilities in the solar plasma induce localized temperature oscillations, but his model showed that while most of the oscillations cancel each other, some reinforce one another and become long-lived temperature variations.

The favored frequencies allow the sun's core temperature to oscillate around its average temperature of 13.6 million degrees Kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says random interactions within the sun's magnetic field could switch the fluctuations from one cycle length to the other.

The research is detailed in the current issue of New Scientist magazine.