The phenomena is well-explained in an article by S. P. Sullivan at Masslive.com:
A burst of plasma sent forth from the sun during Sunday's eruption will hit the upper levels of the Earth's atmosphere. The effect, known as aurora borealis, or Northern Lights, will be "curtains of light shimmering in the sky" as particles in the air, mainly oxygen and nitrogen, are ionized, according to Stephen E. Schneider, head of the astronomy department at the University of Massachusetts.
"Take a look for the glowing, rippling pink or green colors," Schneider said. The lights are expected to first appear sometime late Tuesday night into Wednesday morning, though estimating an arrival time for solar plasma can be difficult.
Here's a link to Sullivan's article about this uncommon cosmic event, with tips for photographers: http://www.masslive.com/living/index.ssf/2010/08/northern_lights_to_light_up_western_mass_skies_tuesday_and_wednesday.html