Astronomy Picture of the Day . ... 1.01.1997 . ... This particular aurora was photographed hovering over the town of Circle, Alaska. Although Aurora might first appear to be moonlit clouds, they only add light to the sky, and hence can not block background stars from view. Called "northern lights" in the northern hemisphere of the Earth , aurora are caused by charged particles streaming from the Sun entering the Earth's atmosphere. ... January . ... January 1997 . ... 1997 1998 . ...