A super telescope, called the Dark Energy Spectroscopic Instrument (DESI) has started the most detailed survey of the cosmos ever undertaken. As part of the 5 year programme, DESI will measure the effect of dark energy on the expansion of the Universe. It will do so, by by obtaining optical spectra for millions of galaxies and quasars by spanning the Universe to 11 billion years and then constructing a 3D map. DESI has 5,000 optical fibres, each working as a mini telescope, enabling it to capture light from 5,000 galaxies, every 20 minutes and allowing it to gauge how much the Universe expanded. 35 million galaxies will be selected to be targeted by DESI, which has been attached to the Mayall 4-meter telescope at Kitt Peak National Observatory in Arizona, US.
Dark energy (and dark matter) makes up 95% of the Universe but scientists have not been able to observe it and know next to nothing about it. However, what we do know is that it is likely to be responsible for the continuous and accelerating expansion of the Universe.