Astronomy Picture of the Day

Explanation: It was Halloween and the sky looked like a creature. Exactly which creature, the astrophotographer was unsure (but possibly you can suggest one). Exactly what caused the eerie apparition was sure: one of the best auroral displays in recent memory. This spectacular aurora had an unusually high degree of detail. Pictured above, the vivid green and purple auroral colours are caused by high atmospheric oxygen and hydrogen reacting to a burst of incoming electrons. Birch trees in Tromsø, Norway formed an also eerie foreground. Many other photogenic aurorae have been triggered by recent energetic flares on the Sun.