Over its 5-year observing lifetime, DESI will measure the spectra of more than 30 million galaxies and quasars covering 14,000 square degrees. The DESI instrument will provide unprecedented multi-object spectroscopy incorporating a novel design.
DESI’s new corrector optics provides a 3-degree-diameter field of view that feeds a focal plate containing 5,000 robotic positioners. The positioners can be reconfigured within 3 minutes to measure the spectra of a new set of galaxies. Optical fibers mounted to the positioners extend 50 meters down the telescope to feed 10 broad-band spectrographs, each containing three detectors. The spectrographs cover a spectral range of 360 nanometers (nm) to 980 nm with a resolution of 2,000 to 5,000, enabling DESI to probe redshifts up to 1.7 for emission line galaxies and 3.5 for the lyman-α spectra from quasars.
The instrument has been mounted on the 4-meter Mayall Telescope in 2018. The construction and integration of the instrument is the result of collaborations between several institutions.