|Organization||European Southern Observatory|
|Logo||-||Wavelength regime||Infrared, Visible light (0.32-12 µm)|
|Location||Still to be determined, but the Chajnantor 'altiplano' east of Antofagasta in Chile has a good chance.|
|Completion||2017 .. 2019|
|Telescope Style||Cassegrain, Coudé|
|Collecting Area||2827 - 7854 m2|
|Focal Length||175 m|
|Primary Mirror||Consists of 3048 hexagonal segments each about ~2 m in size and 15cm thick made of Zerodur.|
|Estimated cost||About €1200 million|
The Overwhelmingly Large Telescope (OWL) is a conceptual design by the European Southern Observatory (ESO) organization for an extremely large telescope, which was intended to have a single aperture of 100 meters in diameter, but was later scaled down to a 60 meter diameter telescope. Because of the complexity and cost of building a telescope of this unprecedented size, ESO has elected to focus on the less ambitious 42 meter diameter European Extremely Large Telescope instead.
While the original 100-m design would not exceed the angular resolving power of interferometric telescopes, it would have exceptional light-gathering and imaging capacity which would greatly increase the depth to which humankind could explore the universe. The OWL could be expected to regularly see astronomical objects with an apparent magnitude of 38; or 1500 times fainter than the faintest object which has been detected by the Hubble Space Telescope.
If built, it would be the largest optical telescope ever constructed. It has been claimed that OWL would have a greater mirror surface area than that of all previous professional telescopes combined.
All proposed designs for the OWL are variations on a segmented mirror, since there is no technology available to build a monolithic 60- or 100-meter mirror. The operation of a segmented mirror is somewhat more complicated than a monolithic one, requiring careful alignment of the segments (a technique called cophasing). Experience gained in existing segmented mirrors (for example, the Keck telescope) suggests that the mirror proposed for the OWL is feasible. However, the projected cost (of around €1.5 billion) was uncomfortably high, and the ESO is now working on a smaller European Extremely Large Telescope around 42m in diameter.
It has been estimated that a telescope with a diameter of 80 meters would be able to spectroscopically analyse Earth-size planets around the 40 nearest sun-like stars. As such, this telescope could help in the exploration of extrasolar planets and extraterrestrial life (because the spectrum from the planets could indicate the presence of molecules indicative of life).