Scientists baffled by sun's deep quiet
Where have all the sunspots gone? Solar scientists thought 2008 was the quietest year for solar activity on record. But 2009 has started out even quieter. The percentage of days without any sunspots visible on the sun's disk has increased this year to 87 percent, up from 73 percent in 2008.
This now ranks as the quietest ebb in the sun's 11-year cycle of rising and falling activity in almost a century. Among the notable effects so far:
* a 50-year low in solar wind pressure, which is allowing more galactic cosmic rays to penetrate the solar system, endangering space-walking astronauts. Lower solar wind pressure also produces fewer auroras.
* a striking slump in solar irradiance, or brightness. It's only 0.02 percent in visible wavelengths, but 6 percent in the ultraviolet. It's cooled and shrunk the upper atmosphere, extending the orbital lifetimes of satellites and junk in low-Earth orbit.
* a 55-year low in solar radio emissions. Nobody seems to understand this one.