High-energy particles from the Sun and from regions beyond the solar system constantly bombard Earth. Thanks to the planet's atmosphere and magnetic field, comsic radiation is not a significant threat to those rooted on terra firma. But airline crew and passengers flying at high altitudes, or over the poles where the Earth's magnetic field provides no protection, are particularly vulnerable to unpredictable flares on the Sun's surface that launch streams of sub-atomic particles toward Earth. The report, "Solar Radiation Alert System," published by the Federal Aviation Administration (FAA) and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder, in July 2005 (www.faa.gov/library/reports/medical/oamtechreports/2000s/media/0514.pdf) details in alert system designed to estimate the ionizing radiation at aircraft flight altitudes and, depending on the resulting dose rate, issue a warning.