“It’s constant work that goes on to make this instrument perform,” said physicist Klaus Honscheid of Ohio State University, an Instrument Scientist on the project,
in a press release. “You have to position each robot to collect the light from galaxies billions of light-years away. Every time I think about this system, I wonder how could we possibly pull that off? The success of DESI as an instrument is something to be very proud of.”
But accomplishing this technical feat wasn’t the only hurdle that DESI had to overcome.
While the basic picture of the sky is visible to anyone who looks up at night, creating accurate maps is a bit trickier. Especially in 3D, because what we see when we look up is a 2D projection of the 3D cosmos. Before DESI could even get started, researchers needed to create a more detailed 2D map of the universe. What followed was a 6-year effort, stitching together more than 1 billion galaxy images taken from over 200,000 telescope images and years of satellite data. The new map comprises an astounding 1 petabyte of data — enough to store 1 million movies.
With that new 2D map in hand, DESI began to survey the sky on May 17, 2021.
Tackling the big question
The universe has been growing ever since it began. This expansion carries all matter, including galaxies, within the cosmos farther apart, like raisins embedded in a rising loaf of raisin bread. As they move farther away, the light reaching us from distant galaxies is stretched into longer and longer wavelengths. Generally, the more stretched, or redshifted, a galaxy’s light, the more distant the galaxy is.
By collecting detailed color images of galaxies, DESI can determine how much the light from each galaxy is redshifted. And this adds the third dimension — depth — to our picture of the universe.
By knowing the distances to galaxies and other bright objects, astronomers can paint a better picture of how the universe came to be the place we see today.