Martin Luther King Jr. Memorial in Washington, DC (© Win McNamee/Getty Images)

Polar bears at play in the Arctic (© Ondrej Prosicky/Shutterstock)

Star trails over Ardez, Graubunden, Switzerland (© Roberto Moiola/Getty Images)

The Radcliffe Camera and All Souls College, University of Oxford, England (© atiger/Shutterstock)

Bản Giốc–Detian Falls on the Quây Sơn River, Vietnam (© Shane P. White/Minden Pictures)

Plum-headed parakeet at Shimoga, Karnataka, India (© Hira Punjabi/Alamy)

Flooded crypt, Basilica of San Francesco, Ravenna, Italy (© Andrea Pucci/Getty Images)

Moeraki Boulders at sunset, South Island, New Zealand (© Douglas Pearson/eStock Photo)

Snow on the Great Wall of China (© View Stock/Alamy)

The US Capitol dome with flags flying at half-staff in honor of former President Jimmy Carter, Washington, DC (© J. David Ake/Getty Images)

Abraham Lake, Alberta, Canada (© Basic Elements Photography/Getty Images)

Heri es-Swani in Meknes, Morocco (© Calin Stan/Shutterstock)

Crescent-tail bigeye fish in the Great Barrier Reef, Australia (© Fred Bavendam/Minden Pictures)

Cottage with Tŵr Mawr Lighthouse in the background, Ynys Llanddwyn, Wales (© Westend61 on Offset/Shutterstock)

Village of Zahara de la Sierra overlooking Zahara-El Gastor Reservoir, Cádiz province, Spain (© SEN LI/Getty Images)

The Great Court of the British Museum, London, England (© Cavan Images/Offset/Shutterstock)

High Peaks Trail in Pinnacles National Park, San Benito County, California (© yhelfman/Getty Images)

Brown pelican, San Diego, California (© Arthur Morris/BIRDS AS ART/Getty Images)

Sunset at White Sands National Park, New Mexico (© Image Professionals GmbH/Alamy)

Neptune's Grotto, Sardinia, Italy (© Carlo Murenu/Getty Images)

Eurasian red squirrel (© Edwin Giesbers/Minden Pictures)

Ad-Deir, Petra, Jordan (© Punnawit Suwuttananun/Getty Images)

Deer Valley at dusk, Park City, Utah (© Adventure_Photo/Getty Images)

Strokkur geyser in Iceland (© John and Tina Reid/Getty Images)

Porto, Portugal (© Starcevic/Getty Images)

European beech forest in Belgium (© Philippe Moes/Minden Pictures)

Zoroaster Temple, Grand Canyon National Park, Arizona (© Nick Lake/Tandem Stills + Motion)

Short-eared owl hunting in heavy snow (© Dilshan Muthalib/Getty Images)

Dragon dance, Wuhan, China (© Miao Jian/Wuhan Morning Post/Visual China Group via Getty Images)

La Brecha de Rolando, Ordesa y Monte Perdido National Park, Spain (© Inaki Relanzon/Nature Picture Library/Alamy)

Plains zebras at sunrise, Mokala National Park, South Africa (© EcoPrint/Shutterstock)