Aurorae are most prominent at high altitudes near the North and South Poles. They can also be seen sometimes at lower latitudes on clear nights, far from city lights; every once in a while—perhaps once every year or so—aurorae can be seen as far south as the lower 48 states of the United States. Displays of aurorae can be amazingly beautiful, varying in color from whitish-green to deep red and taking on forms like streamers, arcs, curtains, and shells.