Nicholas U. Mayall Telescope
The Nicholas U. Mayall Telescope, also known as the Mayall 4-meter Telescope, is a four-meter reflector telescope located at the Kitt Peak National Observatory in Arizona and named after Nicholas U. Mayall. It saw first light on February 27, 1973, and was the second-largest telescope in the world at that time. Initial observers included David Crawford, Nicholas Mayall, and Arthur Hoag. It was dedicated on June 20, 1973 after Mayall's retirement as director. The mirror has an f/2.7 hyperboloidal shape. It is made from a two-foot thick fused quartz disk that is supported in an advanced-design mirror cell. The prime focus has a field of view six times larger than that of the Hale reflector. It is host to the Dark Energy Spectroscopic Instrument. The identical Victor M. Blanco Telescope was later built at Cerro Tololo Inter-American Observatory, in Chile.
The telescope was dedicated in the summer of 1973, at which time it was the second largest telescope by aperture in the world. The telescope was named after Mayall who was the director of Kitt Peak National Observatory for over a decade.
The telescope primary mirror is designed to function as the first element in a Ritchey-Chretien optical design. The telescope was originally designed with three focal point options: the prime focus, a wide-field R/C focus, and a coude focus.
;Planning & Construction
In 1961, after work had moved forward on other telescopes, Mayall proposed an even larger 150-inch mirror telescope for Kitt Peak. Site construction began in 1968, and by 1971 the mirror was delivered to the site. The mirror was made by Owens-Illinois.
The mirror was made of fused quartz, valued for its low coefficient of thermal expansion, and the blank was ground at the Kitt Peak optical lab.
Instruments
Examples of instruments over its lifetime include various spectrographs, Cryogenic Camera, the Phoenix spectrometer, and the DLIRIM.The KNPO Mosaic camera was installed in 1998, and was designed for the prime focus. This camera had eight 2048 × 4096 CCD sensors. This lead to another camera Mosaic II for the CTIO 4-m telescope in the southern hemisphere.
;Mosaic3
Mosaic3 was an imaging camera for the Mayall telescope. This prime focus camera was used for a 3-band survey in support of the upcoming DESI instrument.
;Fourier Transform Spectrograph
One instrument used with telescope was the Fourier Transform Spectrograph. The FTS was used between 1975 and 1995, creating an archive of recorded spectra. It was noted for collecting infrared spectrum before the advent of infrared imaging arrays.
Over the time of its operation 10,000 spectra were taken of 800 different astronomical targets, and these were made available in the SpArc data archive in the early 21st century.
;DESI
In late 2019 the DESI instruments was nearing completion, an instrument designed to help understand dark matter. Dark Matter was theorized by Fritz Zwicky in 1933, based on calculations of star motion that seemed to require more mass dark matter. Zwicky used then largest telescope in the world, the 100-inch Hooker telescope in California for this research.
DESI has five thousand fiber optic sensors, each one being robotically targetable at the focal plane. Planned to examine the nature of millions of galaxies and quasars, the instrument has been a decade in construction and features contributions from hundreds of researchers.
The telescope control software was also upgraded in the 2010s to prepare for DESI.
In October 2019, DESI achieved its first light test and in March was commissioned. Full operations were expected by the end of 2020.
Discoveries & Observations
In 1976 the Mayall Telescope was used to discover methane ice on planet Pluto.The FTS on Mayall was also used to study methane in the outer solar system in the 1980s. The study included observation of monodeutered methane on Titan, a moon of Saturn noted for its thick atmosphere.
The Mayall was also one of several large telescopes that was part of a study of the Andromeda galaxy. The observations helped understand the history of that Galaxy, which turn helps understand Earth's galaxy, the Milky Way.
Contemporaries on commissioning
The Mayall was the second-largest telescope when inaugurated, between the Hale and Shane.Largest telescopes 1973:
| # | Name / Observatory | Image | Aperture | Altitude | First Light | Special advocate |
| 1 | Hale Telescope Palomar Obs. | 200 inch 508 cm | 1713 m | 1949 | George Ellery Hale | |
| 2 | Mayall Telescope Kitt Peak National Obs. | 158 inch 401 cm | 2120 m | 1973 | Nicholas Mayall | |
| 3 | Shane Telescope Lick Observatory | 120 inch 305 cm | 1283 m | 1959 | Nicholas Mayall C. Donald Shane | |
| 4 | Harlan J. Smith Telescope McDonald Observatory | 107 in 270 cm | 2070 m | 1968 | Harlan J. Smith |
Here is the dedication of the telescope with its namesake at the eyepiece: