Observations from Yerkes Observatory during a 55 year period spanning 5 sunspot cycles did confirm that September and March are the most frequent months for auroras and January and July the least likely. This correlation was also apparently described by Mairan in 1733. Most of the solar activity comes from regions of the sun outside the solar equatorial band +/- 10 degrees to either side of the solar equator. The Earth in its orbit is inside this equatorial band during January and July, and when it is at it maximum heliographic latitudes in September and March, the Earth is in the zone of solar activity.
All answers are provided by Dr. Sten Odenwald (Raytheon STX)
NASA IMAGE/POETRY Education and Public Outreach program.