Mapping the universe in 3-D

In 1998, scientists discovered that the universe's expansion is accelerating. Physicists don't know how or why the universe is accelerating outward, but they gave the mysterious force behind this phenomenon a name: dark energy.

Scientists know a great deal about the effects of dark energy, but they don't know what it is. Cosmologists approximate that 68 percent of the universe's total energy must be made of the stuff. One way to get a better handle on dark energy and its effects is to create detailed maps of the universe, plotting its expansion. Scientists,engineersand technicians are currently building the Dark Energy Spectroscopic Instrument, or DESI, to do just that.

DESI will help create the largest 3-D map of galaxies to date, one that will span a third of the entire sky, stretch back 11 billion light-years, and record approximately 35 million galaxies and quasars.

It will measure the spectra of light emanating from galaxies to determine their distances from Earth. Other surveys have created maps that locate galaxies' lateral positions in the sky, but scientists using DESI will be able to take more precise measurements of their distance from us, creating high-resolution, 3-D maps.