The European Extremely Large Telescope (E-ELT), with a main mirror 39 metres in diameter, will be the worldâs biggest eye on the sky when it becomes operational early in the next decade.  The E-ELT will tackle the biggest scientific challenges of our time, and aim for a number of notable firsts, including tracking down Earth-like planets around other stars in the âhabitable zonesâ where life could exist â one of the Holy Grails of modern observational astronomy. The telescope design itself is revolutionary and is based on a novel five-mirror scheme that results in exceptional image quality. The primary mirror consists of almost 800 segments, each 1.4 metres wide, but only 50 mm thick.  The optical design calls for an immense secondary mirror 4.2 metres in diameter, bigger than the primary mirrors of any of ESO's telescopes at La Silla. Adaptive mirrors are incorporated into the optics of the telescope to compensate for the fuzziness in the stellar images introduced by atmospheric turbulence. One of these mirrors is supported by more than 6000 actuators that can distort its shape a thousand times per second. The telescope will have several science instruments. It will be possible to switch from one instrument to another within minutes. The telescope and dome will also be able to change positions on the sky and start a new observation in a very short time. The very detailed design for the E-ELT shown here is preliminary.
