The solar activity cycle is usually defined by sunspot numbers but sunspots are related to magnetic activity in the Sun. Many of these other parameters are also directly affected by magnetism. If these correlations really exist, then it would seem that neutrinos are reacting with the magnetic fields in the heliosphere and magnetosphere. Thus, from this evidence, the solution to the solar neutrino problem is a physical one. Another possibility, rarely discussed, is that the solar neutrino flux is actually constant and it is the cosmic ray background that is varying.
Cosmic rays are more likely to get through to the Earth during periods of low solar activity.
Therefore, neutrinos generated in the Earth's atmosphere by cosmic rays will increase in number during these times. If this cosmic background flux is not correctly subtracted from the total detections, then it will appear that the solar flux is indeed varying with the solar cycle. The image at the top of the page is the Supernova 1987A remnant photographed by the Hubble Space Telescope.