A mass pillow fight in Trafalgar Square in central London on April 5, 2014 on International Pillow Fight Day. (Photo by Jane Scanlan)

The competition, which is run by the Royal Observatory Greenwich in association with BBC Sky at Night Magazine, is now in its sixth year and has received over 2,500 entries. Photo: Centre of the Heart Nebula by Ivan Eder (Hungary). Situated 7500 light years away in the “W”-shaped constellation of Cassiopeia, the Heart Nebula is a vast region of glowing gas, energized by a cluster of young stars at its centre. The image depicts the central region, where dust clouds are being eroded and moulded into rugged shapes by the searing cosmic radiation. (Photo by Ivan Eder)

Some 300 girls and women in India still practise open defecation. Over half the country’s population, 800 million people, do not have access to a toilet that meets basic standards. (Photo by Poulomi Basu/WaterAid)

With the United Nations and Tudor City in the foreground, lightning strikes in the sky over the East River as a major storm approaches New York City July 2, 2014. Tropical Storm Arthur, the first of the Atlantic hurricane season, gathered strength July 20, 2014 and would likely reach hurricane strength over the next couple of days. (Photo by Timothy A. Clary/AFP Photo)

The vendors show the toy of snake at the Spring Festival Temple Fair for celebrating Chinese Lunar New Year of Snake at the Temple of Earth park on February 9, 2013 in Beijing, China. The Chinese Lunar New Year of Snake also known as the Spring Festival, which is based on the Lunisolar Chinese calendar, is celebrated from the first day of the first month of the lunar year and ends with Lantern Festival on the Fifteenth day. (Photo by Feng Li)

The Rainbow Warrior III, the newest ship of the enivornmental conservation organization Greenpeace, makes its way to port on the Elbe River on October 20, 2011 in Hamburg, Germany. The Rainbow Warrior III, 53 meters long, designed by Greenpeace and built in Poland and Germany, is a EUR 23 million project completed last week. (Photo by Sean Gallup/Getty Images)

Wrecked tanks are seen close to the road that leads to the village of Imber on December 31, 2011 on Salisbury Plain, England. (Photo by Matt Cardy/Getty Images)

Life reconstruction of the new oviraptorosaurian dinosaur species Anzu wyliei in its 66 million-year-old environment in western North America as seen in an undated handout illustration by Mark A. Klinger, Carnegie Museum of Natural History. Some 18,000 species, great and small, were discovered in 2014, adding to the 2 million already known, scientists said on May 21, 2015 as they released a “Top 10” list that highlights the diversity of life. Anzu wyliei, one of the top 10, dubbed “the chicken from hell”, is extinct. The feathered dinosaur whose partial skeletons were unearthed in the Dakotas was a contemporary of T. rex and Triceratops. (Photo by Mark A. Klingler/Reuters/Carnegie Museum of Natural History)