Kitt Peak National Observatory in the context of "Nicholas U. Mayall Telescope"

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

As a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for observational data to be plotted on graphs, and general trends recorded. Nearby examples of specific phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, including the distance to a galaxy.

Cosmic voids (also known as dark space) are vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. In spite of their size, most galaxies are not located in voids. This is because most galaxies are gravitationally bound together, creating huge cosmic structures known as galaxy filaments. The cosmological evolution of the void regions differs drastically from the evolution of the universe as a whole: there is a long stage when the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies. Hence, although even the emptiest regions of voids contain more than ~15% of the average matter density of the universe, the voids look almost empty to an observer.

Voids typically have a diameter of 10 to 100 megaparsecs (30 to 300 million light-years); particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompson at the Kitt Peak National Observatory.

David Livingstone Crawford (1931 – July 22, 2024) was an American astronomer.

Crawford had a doctorate in astronomy from the University of Chicago and worked most of his scientific career at Kitt Peak National Observatory in Tucson, Arizona, and the National Optical Astronomical Observatories, where he was emeritus astronomer. He co-founded the International Dark-Sky Association with Tim Hunter in 1988. He won the 2010 Clifford W. Holmes Award for popularizing astronomy. Due to his life-long efforts advocating for dark skies and against light pollution he is regarded as one of the greatest environmentalists of the late 20th and early 21st centuries.

Arthur Allen Hoag (January 28, 1921 - July 17, 1999) was an American astronomer most famous for his discovery of Hoag's Object, a type of ring galaxy, in 1950. He worked at the Naval Ordnance Laboratory, was director of the stellar division of Kitt Peak National Observatory and later the director of Lowell Observatory from 1977-1986. He was also one of the founders of the dark-sky movement.

Kitt Peak (O'odham: Ioligam) is a mountain in the U.S. state of Arizona, and at 6,883 feet (2,098 m) is the highest point in the Quinlan Mountains. It is the location of the Kitt Peak National Observatory. The radio telescope at the observatory is one of ten dishes comprising the Very Long Baseline Array radio telescope.

The peak was named in English by county surveyor George J. Roskruge for his sister, Phillippa, who was the wife of William F. Kitt. On his 1893 Pima County Survey map, Roskruge spelled the name 'Kits'. At the request of the wife of George F. Kitt, the spelling was changed by decision in 1930.

47171 Lempo, or as a binary (47171) Lempo–Hiisi (provisional designation 1999 TC₃₆), is a triple trans-Neptunian object in the Kuiper belt, located in the outermost regions of the Solar System. It was discovered on 1 October 1999, by American astronomers Eric Rubenstein and Louis-Gregory Strolger during an observing run at Kitt Peak National Observatory in Arizona, United States. Rubenstein was searching images taken by Strolger as part of their Nearby Galaxies Supernova Search project. It is classified as a plutino with a 2:3 mean-motion resonance with Neptune and is among the brighter TNOs. It reached perihelion in July 2015. This minor planet was named after Lempo from Finnish mythology.

The system's other two components, Paha /ˈpɑːhɑː/ and Hiisi /ˈhiːsi/, were discovered in 2001 and 2007, respectively, and later named after Lempo's two demon cohorts, Paha and Hiisi.

10199 Chariklo /ˈkærəkloʊ/ is a ringed asteroid or centaur in the outer Solar System. It is the largest known centaur, with a diameter of about 250 km (160 mi). It orbits the Sun between Saturn and Uranus with an orbital period of 62.5 years. It was discovered on 15 February 1997 by the University of Arizona's Spacewatch project at Kitt Peak National Observatory. Chariklo has a dark, reddish surface composed of water ice, silicate minerals, amorphous carbon, and various complex organic compounds (also known as tholins).

Chariklo's ring system consists of two narrow rings of icy particles in orbit around the object. The rings of Chariklo were discovered in 2013, when astronomers observed Chariklo occulting or passing in front of a star. Chariklo was the first minor planet discovered to have rings, and as of 2025, it is one of the four minor planets known to have rings (the three others being 2060 Chiron, Haumea, and Quaoar). It is unknown what keeps Chariklo's rings stable, as it has been predicted that they should decay within a few million years. Astronomers have hypothesized that Chariklo's rings might be maintained by the gravitational influence of yet-undiscovered shepherd moons orbiting Chariklo. The origin of Chariklo's rings is uncertain, with various possible explanations including ejection of surface material via outgassing or tidal disruption of a moon around Chariklo.