Careful analysis of data from a satellite-borne radiation detector has shown that solar flares have a distinct 153-day cycle in their troublesome rages.

At a recent conference in Boston of the American Astronomical Society, University of Chicago physicist John Grunsfeld said the finding could help scientists understand the underlying nature of the sun's violent radiance.Solar flares are sudden bursts of magnetic energy emanating from the sun. Because so much energy is stored in the sun's magnetic fields, large flares lasting just a few minutes may release a thousand times as much energy as is stored in all the nuclear weapons on Earth.

Fortunately, most of the energy is dissipated in the vast reaches of space, but a fraction of the high-energy radiation, including electrically charged protons and electrons, enter Earth's atmosphere, causing magnetic storms and auroras, like the northern lights, and wreaking havoc with radio communications.

Grunsfeld credits the long, reliable stream of data from sensors aboard the international Sun-Earth Explorer spacecraft since 1978 for the finding. The numbers and an unusual statistical test led him to discover "a very significant periodicity of 153 days" in the peaks of solar flares. This pattern runs within another, better-known cycle in the pattern of flares that peaks every 11 years. The next maximum peak in the 11-year cycle is expected to begin later this year.