Overwhelmingly Large Telescope

The Overwhelmingly Large Telescope (OWL) was 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. Because of the complexity and cost of building a telescope of this unprecedented size, ESO has elected to focus on the 39-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 humanity could explore the universe. The OWL could be expected to regularly see astronomical objects with an apparent magnitude of 38; or 1,500 times fainter than the faintest object which has been detected by the Hubble Space Telescope.

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 considered too high, so the ESO is now building the smaller European Extremely Large Telescope around 39 m in diameter.