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Mexico's Popocatepetl volcano spews ash into a starry night

Arturo Andrade / AFP - Getty Images

A cloud of ash belches out of Mexico's Popocatepetl volcano, some 55 km from Mexico City, as seen from Paso de Cortes, in the Mexican central state of Puebla, on May 20. Authorities have raised the alert level to "Yellow Phase Three," the fifth of a seven-stage warning system, restricting access to an area of 12 km around the volcano while preparing evacuation routes and shelters.

Arturo Andrade / AFP - Getty Images