In this October 15, 2014 file photo, Katsu Nakamura, sky division manager for Yamaha USA, moves the RMax unmanned helicopter into position before a demonstration of its aerial application capabilities at the University of California, Davis' Oakville Station test vineyard in Oakville, Calif. Researchers at UC Davis have been studying the effectiveness of the drone's ability for spraying pest control and nutritional materials on the test vineyard in California's Napa Valley. (Photo by Rich Pedroncelli/AP Photo)

French twins Thomas and Vincent (L) Seris take the tram in Bordeaux, November 12, 2014. Born with Xeroderma Pigmentosum (XP), the twins cannot be exposed to the sun and its ultraviolet (UV) light, which could provoke precocious cancers due to an autosomal recessive genetic disorder of DNA repair. Colloquially referred to as Children of the Night (Les Enfants de la Lune) the Seris twins are among 70 to 80 people in France who suffer from the genetic defect. The French association “Les Enfants de la Lune” reports that there are between five and ten thousand such cases in the world. Thomas and Vincent have been testing a new protective mask for the last year which is transparent and ventilated and developed by several hospitals in France. (Photo by Regis Duvignau/Reuters)

Opposition students march against Venezuelan President Nicolas Maduro's government in Caracas February 12, 2015. Venezuelan troops blocked students during marches against Maduro on Thursday as pro-government supporters also rallied on the anniversary of 2014 protests that led to 43 deaths. In Caracas, troops cordoned off scores of students on an unauthorized march to a church where they planned a mass in honour of demonstrators who died. (Photo by Jorge Silva/Reuters)

In this Wednesday, July 23, 2014 file photo, Omaha photographer Lane Hickenbottom photographs the night sky in a pasture near Callaway, Neb. With no moon in the sky, the Milky Way was visible to the naked eye. More than one-third of the world’s population can no longer see the Milky Way because of man-made lights, according to a scientific paper by Light Pollution Science and Technology Institute's Fabio Falchi and his team members, published on Friday, June 10, 2016. (Photo by Travis Heying/The Wichita Eagle via AP Photo)

A soup for the students is pictured during an activity for the end of the school year at the Padre Jose Maria Velaz school in Caracas, Venezuela July 12, 2016. Due to the faltering socialist economy and the plunge in global oil prices, Venezuela has been in recession since early 2014. Due to the faltering socialist economy and the plunge in global oil prices, Venezuela has been in recession since early 2014. It suffers from the world's highest inflation and is experiencing shortages of basic goods, from milk to medicines. (Photo by Carlos Jasso/Reuters)

U.S. Air Force pilots with the Thunderbirds perform the calypso pass maneuver in F-16 Fighting Falcon aircraft during a practice session prior to the Gunfighter Skies air show at Mountain Home Air Force Base, Idaho, September 19 and released September 24, 2014. (Photo by Tech. Sgt. Manuel J. Martinez/Reuters/US Air Force)

A girl walks down the runway during a class at a modelling academy in Caracas, Venezuela, on September 20, 2014. Venezuela's famed models and aspiring beauty queens are struggling to doll themselves up. In a country that glorifies voluptuous women and opulent beauty pageants, even basics like deodorant are now at times tricky to find as strict currency controls have led to a scarcity of dollars for imported goods. (Photo by Carlos Garcia Rawlins/Reuters)

A combination photo shows some of the colourful doors seen in Rabat's Medina and Kasbah of the Udayas, September 2014. UNESCO made Rabat a World Heritage Site two years ago and media and tour operators call it a “must-see destination”. But it seems the tourist hordes have yet to find out. While visitors are getting squeezed through the better-known sites of Marrakesh and Fez, the old part of Rabat - with its beautiful Medina and Kasbah of the Udayas - remains an almost unspoiled oasis of calm. Smaller and more compact, its labyrinths of streets, passages and dead ends are a treasure trove of shapes and colours, of moments begging to be caught by the photographer's lens. (Photo by Damir Sagolj/Reuters)