Right now, in a browser tab, you can zoom through 75% of the sky across a 5.6-trillion-pixel image containing nearly 4 billion stars, galaxies, quasars, and asteroids. No subscription. No PhD required. Just the Legacy Survey Sky Viewer and whatever’s left of your afternoon.
That’s the quietly staggering thing about what the DESI Legacy Imaging Surveys released this August: the largest 2D color map of the universe ever assembled is also a public tool. Thirteen years of work. Open to anyone.
What You’re Actually Looking At
Three surveys, one satellite, and 2,285 nights of sky-watching produced something you can explore before lunch.
Building this required 263,407 telescope exposures gathered across 2,285 nights from three ground-based survey operations — DECaLS in Chile, plus MzLS and BASS in Arizona — supplemented with infrared data from NASA’s WISE satellite. The map covers about 75% of the sky, not 100%, because the Milky Way’s own dense dust band sits in the way like a cosmic bouncer. Astronomers deliberately aimed above and below that plane to capture clean views of the extragalactic universe.
- 5.6 trillion pixels — the largest 2D color map ever released to the public
- Nearly 4 billion objects: stars, galaxies, quasars, and more
- Over 1,800 scientific papers already cite this dataset
- Freely accessible via the Legacy Survey Sky Viewer — zoom, pan, search any coordinates
“When you’re working with astronomical objects today, you often start by pulling up the Legacy Imaging Viewer to see what you’re looking at,” said David Schlegel, LBNL researcher and Legacy Surveys co-lead.
What the Data Is Starting to Suggest – and Why It Matters
The 2D map is only the beginning; what DESI does with it is where things get genuinely interesting.
That map is the foundation. DESI’s real instrument — 5,000 robot-controlled fiber positioners on the Mayall 4-meter telescope — uses it to build a 3D map of the cosmos. It measures distances to tens of millions of galaxies across 11 billion years of cosmic history.
That data probes dark energy, the unknown force accelerating the universe’s expansion. DESI measures baryon acoustic oscillations — a repeating pattern in galaxy clustering that acts like a cosmic ruler for tracking expansion rates over time. Three years of data, combined with supernova and cosmic microwave background measurements, show 3–4 sigma hints that dark energy may be weakening. Analyses suggest it was roughly 10% stronger when the universe was about 70% of its current age.
That’s not a discovery. The gold standard is 5 sigma. Some cosmologists also caution that conclusions depend heavily on modeling assumptions, and DESI alone remains consistent with a constant dark energy.
Full survey results targeting 47–50 million galaxies arrive around 2027. That analysis will sharpen or bury the evolving dark energy theory entirely.
“These data are fundamental to the investigation of the expansion history of the universe,” said Arjun Dey, NOIRLab astronomer and Legacy Surveys co-director. “But the skies belong to everyone, and this survey gives everyone the chance to marvel at their wonders.”
The Legacy Survey Sky Viewer is open right now. Copeland’s Septuplets galaxy group in Leo is a good first stop — seven galaxies tangled together, visible in a browser, free, waiting.
