A giant storm cloud can be seen in the sky above swimmers near Mollymook Beach, south of Sydney, March 5, 2014. (Photo by David Gray/Reuters)

A man flies a kite on the Bund while buildings of Pudong's Lujiazui financial district stand across the Huangpu River as the sun rises in Shanghai, China, on Friday, October 2, 2015. (Photo by Qilai Shen/Bloomberg)

The rising sun illuminates the sky above the spires of a church in Vienna, Austria, November 17, 2015. (Photo by Heinz-Peter Bader/Reuters)

A photographer takes a snapshot of the reflection of balloons as they take off from Balloon fiesta park in Corrales, N.M., near a north diversion channel reservoir Wednesday, October 7, 2015. (Photo by Roberto E. Rosales/Albuquerque Journal via AP Photo)

In this photo taken late Thursday, May 7, 2015, a prison guard, left, and seated inmates cast shadows on a wall while waiting for the beginning of a rock concert by Romanian band Pro Musica, inside the Popa Sapca jail in Timisoara, western Romania. (Photo by Adi Piclisan/AP Photo)

A young girls holds a ballot during the Greek referendum in Athens on July 5, 2015. Greek voters headed to the polls today to vote in a historic, tightly fought referendum on whether to accept worsening austerity in exchange for more bailout funds, in a gamble that could see it crash out of the euro. (Photo by Aris Messinis/AFP Photo)

A picture made available on 17 July 2015 shows the bright line of the Milky Way above the old oaks at the Rogalin landscape Park in Rogalin village, near Poznan, on the night of 16 July 2015. (Photo by Lukasz Ogrodowczyk/EPA)

A reveler jumps over a bonfire during the night of San Juan in Alcobendas near Madrid, Spain, Wednesday, June 24, 2015. The San Juan night coincides with the Summer solstice and it's the welcome to Summer. This celebration takes place during the shortest night of the year in almost all cities and towns of Spain. (Photo by Andres Kudacki/AP Photo)