The Earth has an associated magnetic field, referred to as the geomagnetic field, which is caused by electric currents both within the Earth and in the area surrounding the Earth. The geomagnetic field is what causes a compass to point north. The interaction of the geomagnetic field with the solar wind is what gives us aurora - the Northern or Southern Lights. Why is geomagnetism considered a geologic hazard? Occasionally the earth experiences a "magnetic storm", which is a rapid variation in the geomagnetic field, caused either by a gust in the 'solar wind' or by a temporary linking of the Sun's magnetic field with the geomagnetic field. Magnetic storms can disturb long-range radio communication, degrade global positioning systems, damage satellites, affect long-distance pipelines, and produce surges on electric power grids resulting in magnetic storms can expose astronauts and high-altitude pilots to increased levels of radiation. Large magnetic storms can produce dramatic auroral displays. Variations in the magnetic field don't have a direct impact on human health, but do affect the technology that is important to our modern society. Because the geomagnetic field covers the entire Earth, problems caused by geomagnetic storms can occur almost anywhere. The 'National Oceanic and Atmospheric Administration' (NOAA), 'National Weather Service, Space Environment Center (SEC)' monitors geomagnetic storm activity and provides real-time information on their 'Space Weather Now' site. The SEC has defined five types of 'solar radiation storms', ranging from mild to extreme; their definitions include a description of the possible damaging effects of each class of magnetic storm