A consortium of 15 European countries have agreed to spend 1 billion euros to build the largest optical telescope in the world. The European Extremely Large Telescope, or E-ELT, will be built on a mountaintop in Chile and is planned to come online in 2022. It will have a 39.3-meter mirror and its 978-square-meter light collecting area will collect 15 times more light than other current telescopes. The mirror will consist of 798 hexagonal segments 1.45 meters long but only 50 millimeters thick. It will be designed so that its shape can be adjusted up to 1,000 times per second to compensate for atmospheric distortion. Astronomers hope to use the E-ELT to search for planets around other stars and to do "stellar archaeology," meaning to observe the properties of galaxies as they formed shortly after the Big Bang.