Solar flares are spectacular outbursts associated with sunspot groups, particularly with the earlier stages of large, active groups. They may be viewed with a monochromatic filter or the spectrohelioscope, where they appear as very bright areas of the chromosphere. Because of the intense ultraviolet radiations, the upper atmosphere of the earth is strongly ionized, causing a pronounced fade out of high-frequency radio reception. Powerful radio emissions are associated with the flares in the 10 to 300 megacycles per second range. Aurora displays and geomagnetic disturbances may be expected within two days after the flare appears.