Geomagnetic storms are the cause of auroras. Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. The frequency of geomagnetic storms increases and decreases with the sunspot cycle. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Several space weather phenomena are associated with geomagnetic storms. Geomagnetic storms occasionally damage electronic components on spacecraft. Rapidly fluctuating geomagnetic fields can produce geomagnetically induced currents in pipelines. They also create aurorae seen at high latitudes in an oval surrounding the geomagnetic poles. Evening TEP is quenched by moderate to severe geomagnetic disturbances. The flux is dependent on geomagnetic latitude, with a maximum near the magnetic poles. It therefore has a large effect on the electrodynamics of geomagnetic storms. Telegraph lines in the past were affected by geomagnetic storms. It was one of the strongest geomagnetic storms in years. Aircraft flying polar routes near the geomagnetic poles are at particular risk. Ar dating was used to calibrate the geomagnetic polarity time scale.