Solar

The world's largest solar-powered boat, "MS Turanor PlanetSolar" sails through the Corinth Canal near the town of Corinth on July 28, 2014.  The boat arrived to Greece as part of a joint archaeological project focused on underwater exploration off one of Europe's oldest human occupation sites, the Franchthi cave in the Argolid, southeast Peloponnese. The project is taking place in one of Greece's richest archaelogical areas, the Argolid, known for its major palatial complexes in the Bronze Age that include Mycenae and Tiryns and later, classical-era city-states and sites like Argos and the ancient-theatre site of Epidaurus.

Valerie Gache/AFP

The world’s largest solar-powered boat, “MS Turanor PlanetSolar” sails through the Corinth Canal near the town of Corinth on Monday. The boat arrived to Greece as part of a joint archaeological project focused on underwater exploration off one of Europe’s oldest human occupation sites, the Franchthi cave in the Argolid, southeast Peloponnese

Experimental aircraft 'Solar Impulse 2',

Laurent Gilleiron/EPA

The experimental aircraft “Solar Impulse 2″, HB-SIB, during solar generator tests at an air base in Payerne, Switzerland, on Monday. The project aims to achieve the first circumnavigation of the world with an aircraft powered only by solar energy.

Solar Impulse, piloted by AndrÈ Borschberg, takes flight during the second leg of the 2013 Across America mission, at dawn, Wednesday, May 22, 2013, from Sky Harbor International Airport in Phoenix. The solar powered aircraft is scheduled to land at Dallas/Fort Worth International Airport on Thursday May 23. The plane's creators, Bertrand Piccard and Borschberg, said the trip is the first attempt by a solar airplane capable of flying day and night without fuel to fly across America. (AP Photo/Matt York)

Matt York/AP

Solar Impulse, piloted by André Borschberg, takes flight during the second leg of the 2013 Across America mission at dawn on Wednesday from Sky Harbor International Airport in Phoenix, Arizona. Read more

A man look up at a starry night at Kielder Water, Northumberland.

Tom White/PA

Stargazer delight: a man takes in the beautiful spectacle of the unusually clear night sky over Kielder Water, Northumberland, northeast England, on Tuesday Read more