The 45-year-old Nicholas U. Mayall Telescope at Kitt Peak National Observatory in Arizona is now an active construction site. The telescope is undergoing a major renovation to prepare for the installation of the Dark Energy Spectroscopic Instrument (DESI). DESI will create the largest 3-D map of the universe and help explain dark energy, which is responsible for the accelerating expansion of the universe. The Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) is leading the DESI collaboration, which includes participation from about 465 researchers and 71 institutions worldwide.

Berkeley Lab photographer Marilyn Sargent visited Kitt Peak and the Mayall Telescope, as well as the DESI collaboration meeting in Tucson, in May and captured these images.
Entrance to the Kitt Peak National Observatory in Tucson, Arizona.
Sonia Karkar and David Sprayberry discuss the installation of the calibration lamps on the top ring of the Mayall 4-Meter Telescope for DESI.
Inside the center of the Mayall 4-Meter Telescope is a concrete tower that holds up the structure.
Inside the lower level of the Mayall 4-Meter Telescope at Kitt Peak National Observatory.
Calibration lamps, that recently arrived from France, will be installed on the top ring of the Mayall 4-Meter Telescope.
The lens of the Mayall 4-Meter Telescope is in storage until it can be repaired and cleaned before it is returned to its position to be used for DESI.
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