DESI
The Dark Energy Spectroscopic Instrument
By accurately measuring the expansion history over the past 11 billion years, DESI’s scientific goal is to constrain possible models of dark energy. In order to accomplish this goal, DESI will measure the position and receding velocity of about 40 million galaxies. These galaxies will have been pre-selected by studying deep images of the DESI survey area, or footprint, taken during observing campaigns before DESI starts up.