Space and Earth Sciences News

Sidebar: 'Solar Constant' is an OxymoronAstronomers were once so convinced of the sun's constancy, they called the irradiance of the sun "the solar constant," and they set out to measure it as they would any constant of Nature. By definition, the solar constant is the amount of solar energy deposited at the top of Earth's atmosphere in units of watts per meter-squared. All wavelengths of radiation are included?radio, infrared, visible light, ultraviolet, x-rays and so on. The approximate value of the solar constant is 1361 W/m2.Clouds, atmospheric absorption and other factors complicate measurements from Earth's surface, so NASA has taken the measuring devices to space. Today, VIRGO, ACRIM and SORCE are making measurements with precisions approaching 10 parts per million per year. Future instruments scheduled for flight on NASA's Glory and NOAA's NPOESS spacecraft aim for even higher precisions.To the amazement of many researchers, the solar constant has turned out to be not constant."'Solar co