Planeterrella demonstrating the Earth's Northern Lights. The color of the aurora is purple because of the nitrogen in the ambient air that the Planeterrella is using.
Planeterrella demonstrating the Earth’s Northern Lights. The color of the aurora is purple because of the nitrogen in the ambient air that the Planeterrella is using. The aurora on Earth is usually green, due to reactions with oxygen in the atmosphere. Credit: Courtesy of Guillaume Gronoff