A 17th century Central Tibetan thangka (painted or embroidered banner) of Guhyasamaja Akshobhyavajra, from the Guhyasamāja tantra, a tantra whose practice is important to many schools of Tibetan Buddhism. The Guhyasamaja ("Secret Assembly") tantra was developed at an early date in history to aid the Buddhist practitioner in understanding and practicing Tantric Buddhism to attain enlightenment. These are the basic texts of the Tantric—an esoteric and highly symbolic—form of Buddhism, which developed in India and became dominant in Tibet.

Artist: Unknown

A Braunvieh cow wearing a cow bell below Fuorcla Sesvenna in the Engadin, Switzerland. Of Swiss origin, these cows were imported to the United States in the 19th century where they became the origin of the modern Brown Swiss cattle breed. Since the 1960s, Brown Swiss cattle have been crossed back into the Braunvieh stock of Europe. They are commonly various shades of brown in colour with lighter points.

Photo credit: Daniel Schwen

The Yellowish Flycatcher (Empidonax flavescens) is a small passerine bird in the tyrant flycatcher family. It breeds in highlands from southeastern Mexico south to western Panama. Its upper parts are olive-green and the underparts are yellow with an ochre tint to the big breast.

Photo credit: Mdf

A daguerreotype from the 1850s of the Ben Campbell, a paddle steamer—a ship or boat driven by a steam engine that uses one or more paddle wheels to develop thrust for propulsion. The paddle wheel was the first form of mechanical propulsion for a boat, but has now been almost entirely superseded by more modern forms of marine propulsion.

Daguerreotype credit: Unknown

Video footage taken from the gun camera of a United States Army Apache helicopter on active duty in Iraq and showing the killing of people whom the U.S. military regarded as Iraqi insurgents, and originally shown on ABC Television on January 9, 2004. This incident has been alleged to be a violation of human rights in post-invasion Iraq.

Film credit: United States Army

Crepuscular rays streaming through trees in Golden Gate Park, San Francisco, California. These light beams are seemingly diverging columns of sunlit air separated by darker shadowed regions. Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction, reflection, and scattering.

Photo credit: Mila Zinkova

The face of a Dungeness crab (Cancer magister), a common crab found from the Aleutian Islands in Alaska to Santa Cruz, California. The two eyes sit on eyestalks, with two antennules on either side of the rostrum (center, above the mouth).

Photo credit: Kevin Cole

A map of Arches National Park near Moab, Utah, United States, detailing the location of many of the more well known natural arches, as well as many other physical features. The park is known for preserving over 2,000 arches, including the world-famous Delicate Arch. It is 119 square miles (310 km²) in size. Its highest elevation is 5,653 feet (1,723 m) at Elephant Butte, and its lowest elevation is 4,085 feet (1,245 m) at the visitor center. Since 1970, forty-three arches have toppled because of erosion. The park receives 10 inches (250 mm) of rain a year on average.

Map credit: Justin Morris

Illustration of the Ptolemaic geocentric model of the Universe (the theory that the Earth is the center of the universe) by Portuguese cosmographer and cartographer Bartolomeu Velho. Taken from his treatise Cosmographia, made in Paris, 1568. Notice the distances of the bodies to the centre of the Earth (left) and the times of revolution, in years (right).

Photo credit: Joaquim Alves Gaspar

Ludwig Schnorr von Carolsfeld and his wife Malvina as the title characters of Richard Wagner's Tristan und Isolde, sometime during the opera's initial run, though, given the demands of early photography, most likely not in an actual performance. The opera was extremely difficult on its leads—it had to be delayed when Malvina temporarily lost her voice, and Ludwig died three weeks after the fourth show.

Photo credit: Joseph Albert

Charles Griffin was a career officer in the United States Army and a Union general in the American Civil War. He rose to command a corps in the Army of the Potomac and fought in many of the key campaigns in the Eastern Theater.

After the war, he commanded the Department of Texas during Reconstruction. He proved to be an ardent supporter of the Congressional policies of the Radical Republicans and of freedmen's rights, and controversially disqualified a number of antebellum state officeholders in Texas, replacing them with loyal Unionists.

Photo credit: Mathew Brady or Levin Corbin Handy