Composite image of the total solar eclipse of August 21st 2017, from Idaho Falls, Idaho, USA. At left the Moon is gradually hiding the Sun, totality is at centre, and at right the Moon is moving away from the Sun. This eclipse tracked across a narrow portion of the contiguous United States from Lincoln Beach, Oregon, in the north west, to Charleston, South Carolina, in the south east. A partial solar eclipse was visible across the entire North American continent. Solar eclipses usually occur less than once a year, and can only be seen from a small area of the Earths surface.Dr Juerg AleanScience Photo Library