Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is a scientific research instrument for conducting spectrographic astronomical surveys of distant galaxies. Its main components are a focal plane containing 5,000 fiber-positioning robots, and a bank of spectrographs which are fed by the fibers. The instrument enables an experiment to probe the expansion history of the universe and the mysterious physics of dark energy. The main DESI survey started in May 2021. DESI sits at an elevation of 6,880 feet (2,100 m), where it has been retrofitted onto the Mayall Telescope on top of Kitt Peak in the Sonoran Desert, which is located 55 miles (89 km) from Tucson, Arizona, United States.

In March 2025, the DESI collaboration released Data Release 1 (DR1), containing spectra and redshifts for 18.7 million objects observed during the first 13 months of the main survey, making it the largest spectroscopic redshift dataset released at the time.

Analysis of DESI's first three years of cosmological data, published in 2025, strengthened evidence that dark energy may evolve over cosmic time rather than behaving as a constant cosmological constant.

In 2026, DESI completed its five-year primary survey after mapping more than 47 million galaxies and quasars, exceeding its original design goals.

The instrument is operated by the Lawrence Berkeley National Laboratory under funding from the U.S. Department of Energy's Office of Science. Construction of the instrument was principally funded by the U.S. Department of Energy's Office of Science, and by other numerous sources including the U.S. National Science Foundation, the British Science and Technology Facilities Council, France's Alternative Energies and Atomic Energy Commission, Mexico's National Council of Science and Technology, Spain's Ministry of Science and Innovation, by the Gordon and Betty Moore Foundation, by the Heising-Simons Foundation, and by collaborating institutions worldwide.