Such interaction occurs in zones surrounding the Earth's magnetic poles.
Auroras take many forms, including luminous curtains, arcs, bands, and patches.
The uniform arc is the most stable form of aurora, sometimes persisting for hours without noticeable variation. However, in a great display other forms appear, commonly undergoing dramatic variation. The lower edges of the arcs and folds are usually much more sharply defined than the upper parts. Greenish rays may cover most of the sky polewards of the magnetic zenith, ending in an arc that is usually folded and sometimes edged with a lower red border that may ripple like drapery. The display ends with a poleward retreat of the auroral forms, the rays gradually degenerating into diffuse areas of white light.