Total solar eclipse, composite of solar disc and corona. The corona is a cloud of low-density plasma (hot ions) surrounding the Sun. Normally it is not visible, being obscured by the brightness of the Sun's visible surface, but it is revealed during a total solar eclipse. Here, the solar disc (including visible sunspots) has been overlaid on an image of the corona at totality. The moment of totality lasts for only a few minutes. Total solar eclipses usually occur less than once a year, and can only be seen from a small area of the Earth's surface. This total solar eclipse was observed from the USA on 21 August 2017. Totality lasted for just over 2.5 minutes. The time from first contact to last contact was just over 3 hours. Photographed from Idaho.