DESI Outreach

The Dark Energy Spectroscopic Instrument is measuring the expansion history of the universe by mapping where galaxies are. These pages explain how that actually works — written for anyone curious, with no assumption of a physics background.

A wedge-shaped slice of the universe mapped by DESI Data Release 1, plotted in right ascension and redshift out to z of about 4. Hundreds of thousands of colored points trace large-scale structure: yellow bright galaxies nearest Earth, then orange luminous red galaxies, blue emission-line galaxies, and green quasars furthest out. — A slice of the universe mapped by DESI Data Release 1, out to z ≈ 4. Colors mark the four major samples — bright galaxies, luminous red galaxies, emission-line galaxies and quasars. The inset shows the cosmic web, and represents less than 0.1% of the survey volume. Figure 1 from Data Release 1 of the Dark Energy Spectroscopic Instrument, DESI Collaboration, *The Astronomical Journal* 171, 285 (2026).

Pages

How DESI works

The light path from a distant galaxy to a charge-coupled device: the Mayall telescope, 5,000 robotic fiber positioners, the spectrographs, and what actually lands on a CCD — with simulations and the Python source that produced them.

Galactic tracers

The four kinds of object DESI measures — bright galaxies, luminous red galaxies, emission-line galaxies and quasars — what each one looks like, and the spectral features that give away its distance.

Results

What the map has actually shown: baryon acoustic oscillations as a standard ruler, full-shape clustering, the Lyman-α forest, and what they jointly say about dark energy and the neutrino masses.

Data Release 1

18.7 million high-confidence redshifts from the first thirteen months of the survey — the largest three-dimensional map of the universe yet made, and public.

The Hubble tension

Two ways to measure how fast the universe expands, and two answers that do not overlap. The distance-ladder network, thirteen routes through it, and what each one gives for H₀.

ΛCDM

The standard cosmological model in six parameters, the cosmic timeline from the Planck era to the dark-energy era, and how the 150 Mpc standard ruler is frozen in at recombination.

The Boston University DESI group site carries the group pages and internal resources.