The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. Being approximately 220,000 light years across, Andromeda is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 44 other smaller galaxies. Despite earlier findings that suggested that the Milky Way contains more dark matter and could be the largest in the grouping, the 2006 observations by the Spitzer Space Telescope revealed that Andromeda contains one trillion (1012) stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion.

El Capitan is a vertical rock formation in Yosemite National Park, located on the north side of Yosemite Valley, near its western end. The granite monolith extends about 3,000 feet (900 m) from base to summit along its tallest face and is one of the world's favorite challenges for rock climbers and BASE jumpers.

The Middle Cathedral Rock is a prominent rock face on the south side of Yosemite Valley, California. El Capitan lies due north of Middle Cathedral. Middle Cathedral's East Buttress Route is recognized in the historic climbing text Fifty Classic Climbs of North America.