Astronomy Picture of the Day

Explanation: Few aurorae show this level of detail. Above, a standard digital camera captured a particularly active and colourful auroral corona that occurred last week above Alberta, Canada. With a shape reminiscent of a flower, the spectacular aurora had an unusually high degree of detail. The vivid green and purple auroral colours are caused by high atmospheric oxygen and hydrogen reacting to a burst of incoming electrons. Many photogenic aurorae have been triggered from a solar wind stream that recently passed the Earth. The aurorae were unexpected because the initiating Sun has been unusually quiet of late.