Two young male polar bears, Churchill, Manitoba, Canada (© Cheryl Ramalho/Getty Images)

Dall sheep rams at Polychrome Pass, Denali National Park, Alaska (© Patrick J. Endres/Getty Images)

Autumn leaves coated with frost (© sagarmanis/Getty Images)

Navy Day celebration at Gateway of India, Mumbai (© Dinodia Photos/Alamy Stock Photo)

Salzburg with Salzach river, Austria (© MacEaton/Alamy)

An 1840 design for the Analytical Engine by Charles Babbage (© Science & Society Picture Library/Getty Images)

Mother cheetah and her cub in the Maasai Mara nature reserve, Kenya (© gudkovandrey/Adobe Stock)

Château du Haut-Kœnigsbourg, Alsace, France (© Leonid Andronov/Shutterstock)

Glowworms in Blue Mountains National Park, Australia (© Leelakajonkij/Getty Images)

Arctic fox in Dovrefjell-Sunndalsfjella National Park, Norway (© Andy Trowbridge/Minden Pictures)

The shadow of Mount Everest over the western Himalayas in Nepal (© Kent Karvey/KH Films, Inc./Tandem Stills + Motion)

Wicker fields in Cañamares, Spain (© David Santiago Garcia/Alamy)

Old Town and El Panecillo Hill in Quito, Ecuador (© Karol Kozlowski/plainpicture)

Old Town and El Panecillo Hill in Quito, Ecuador (© Karol Kozlowski/plainpicture)

The chapel and hermitage of Santa Justa in Cantabria, Spain (© Luis Miguel Martin/Getty Images)

Indian rhinoceros in Kaziranga National Park, India (© Abhishek Singh/Moment/Getty Images)

Christmas-themed beach huts in Bournemouth, England (© Allouphoto/Alamy)

The December full moon seen through holiday lights (© Jesus Merida/Getty Images)

Anjuna Beach in Goa, India (© Dmitry Rukhlenko/Shutterstock)

Linn of Quoich瀑布旁的碗状岩石洞，苏格兰阿伯丁郡 (© AWL Images/Danita Delimont)

Linn of Quoich, Aberdeenshire, Scotland (© AWL Images/Danita Delimont)

Winter scene illuminated on the Palais de l'Isle in Annecy, Haute Savoie, France (© blickwinkel/Alamy)

Jog Falls in Karnataka, India (© Rajesh Vijayarajan Photography/Moment Open/Getty Images)

Trees on the northern slope of Mount Khomyak in the Carpathian Mountains, Ukraine (© panaramka/Getty Images)

解析機関の設計図, イギリス ロンドン (© Science & Society Picture Library/Getty Images)

Snow buntings flock during a snowstorm in New York (© Marie Read/Minden Pictures)

Snow buntings, New York, USA (© Marie Read/Minden Pictures)

Mountain goats in the Yukon, Canada (© Mark Newman/Getty Images)

Westerheversand Lighthouse in Westerhever, Germany (© Sandra Bartocha/Minden Pictures)

Bonfire to celebrate New Year's Eve in 2014 in Reykjavik, Iceland (© Ragnar Th Sigurdsson/Alamy)

Harp seal sleeping at Jones Beach, Long Island, New York (© Vicki Jauron, Babylon and Beyond Photography/Getty Images)