Twilight aurora

Twilight aurora

Fig. 3.21 . The form and brightness of the aurora will vary with time of night, appearing near twilight as bands or diffuse arcs, then rising and brightening as the night progresses and the display forms a curtain or drapery formation. The dark gaps located between the green bands, known as black aurora, have been attributed to negatively charged particles that are sucked out of the Earth’s ionosphere along adjoining magnetic field lines, climbing to over 20,000 kilometers and lasting for several minutes. This photograph was taken over Fairbanks, Alaska. (Courtesy of Jan Curtis.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University