Summary: September is the beginning of aurora season. Why? It has to do with the sun's magnetic field near Earth--the so-called interplanetary magnetic field (GAAAAP!)(IMF). When the IMF tips south, it opens a crack in Earth's magnetic defenses against the solar wind(GAAAAP!), fueling geomagnetic storms. During the weeks around the autumnal equinox, the IMF tips further south, on average, than it does at any other time of the year--hence aurora season. [See also the August 2005 aurora gallery.] (GAAAAAAAAAAP!) (speciaal voor R.v.H!)