British Gas engineer Martin Caulfield, 69, services and cleans a gas lamp in front of Big Ben on October 31, 2011 in London, England. Caulfield has been looking after the traditional lights since 1982. There are still around 1600 left in the capital. (Photo by Matthew Lloyd/Getty Images)

People stand under a giant Czech flag as they arrive to light candles at the base of a statue of St. Wenceslas to commemorate the death of former Czech President Vaclav Havel on December 18, 2011 in Prague, Czech Republic. Havel, who led the Velvet Revolution that forced communist rule in Czechoslovakia to crumble in 1989, died in the early morning today in his sleep at the age of 75. (Photo by Sean Gallup/Getty Images)

An image produced by the Hubble telescope of the perfectly “edge-on” galaxy, or NGC 4013, March 1, 2001. This new Hubble picture reveals, with great detail, huge clouds of dust and gas extending along, as well as far above, the galaxy's main disk. NGC 4013 is a spiral galaxy, similar to the Milky Way, lying some 55 million light-years from Earth in the direction of the constellation Ursa Major. Viewed face-on, it would look like a nearly circular pinwheel, but NGC 4013 happens to be seen edge-on from our vantage point. Even at 55 million light-years, the galaxy is larger than Hubble's field of view, and the image shows only a little more than half of the object, albeit with unprecedented detail. (Photo Courtesy of NASA/Newsmakers)

A tale of two foxes. Surprising behaviour, witnessed in Wapusk national park, on Hudson Bay, Canada, in early winter. Red foxes don’t actively hunt Arctic foxes, but where the ranges of two predators overlap, there can be conflict. Though the light was poor, the snow-covered tundra provided the backdrop for the moment that the red fox paused with the smaller fox in its mouth in a grim pose. (Photo by Don Gutoski/2015 Wildlife Photographer of the Year)

The Museum of Feelings doesn't really have “exhibits" in the conventional sense; rather, visitors move from one themed alcove to another, five in total, each with its own distinctive aroma. The “Optimistic Room," bathed in vivid pink and purple light, is little more than a lightshow, with patrons using small reflective panels to bounce light around the room. Here: People interact in the “optimistic” room at the Museum of Feelings, a pop-up installation in New York, December 15, 2015. (Photo by Stephanie Keith/Reuters)

Number 10. BELL H-13 SIOUX was a two-bladed, single engine, light helicopter built by Bell Helicopter. Westland Aircraft manufactured the Sioux under license for the British military as the Sioux AH.1 and HT. In 1947, the United States Air Force ordered the improved Bell Model 47A. Most were designated YR-13 and three winterized versions were designated YR-13A. The United States Army first ordered Bell 47s in 1948 under the designation H-13. These would later receive the name Sioux. The Bell-built H-13 B is seen airborne in this April 29, 1951 photo. The helicopter is equipped with a 173 horsepower engine, cruises at 85 miles per hour, climbs 900 feet in a minute and has a service ceiling of 11,500 feet. (Photo by AP Photo)

Divers swim beside millions of silverside fish at Devil's Grotto, Cayman Islands. Swimming in unison, millions of silverside fish dwarf the divers. The fish create waves of silver light as they move around the grottos that lie beneath the surface of the Caribbean Sea. These amazing photographs were captured by Belgian photographer Ellen Cuylaerts, 44, on a diving trip to the Devil's Grotto, Cayman Islands. (Photo by Ellen Cuylaerts/This is Guavo Media)