Astronomy Picture of the Day . ... 17.05.2001 . ... In a new twist to this solar neutrino saga, an analysis of data from the GALLEX / GNO neutrino detector finds a solar neutrino flux that varies over about 27 days ... approximately matching the Sun's rotation period. In fact, since different parts of the Sun rotate at different rates, the neutrino flux variations match most exactly the rotation rates of the areas shown in red on this colorful cross-sectional map of the solar interior rotation . ...