It took three sky surveys—conducted at telescopes in two continents, covering one-third of the visible sky, and requiring almost 1,000 observing nights—to prepare for a new project that will create the largest 3-D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion.
Source:
https://phys.org/news/2019-07-sky-surveys-dark-energy-spectroscopic.html