The northern lights, or aurora borealis, are visible over Lake Washington, in Renton, Wash.(Lindsey Wasson / AP)

When conditions are just right, the dark night sky can light up with a curtain or ribbon of green light waving across the sky.

These are the northern lights, and they happen when solar winds from the sun crash into the atmosphere, causing an eerie and awe-inspiring green glow.

Dr. Elizabeth MacDonald is a space physicist at Nasa Goddard, and she studies the northern lights. She’s the special guest at the Boise State Physics First Friday Astronomy Talk this Friday, and she joined Idaho Matters for a preview.