Overwhelmingly Large Telescope
Overwhelmingly Large Telescope ( OWL ) was the working title of a telescope study by the European Southern Observatory (ESO). The diameter of the primary mirror of the telescope should be 100 m. After it has a Very Large Telescope ( Engl. For Very Large Telescope was just VLT), to the new project called something self-deprecating Overwhelmingly Large Telescope ( Overwhelming Large Telescope ). At the same time, the name alludes to the owl's good night vision skills. Like the EURO-50 study, the OWL has not been pursued any further since the end of 2005. Instead, the Extremely Large Telescope with a 39 m mirror diameter will be installed.
Proportions
This earth-based optical telescope would have a primary mirror 100 m in diameter and thus about a hundred times the area and thus a hundred times the light collecting capacity of the largest telescope mirrors at that time ( Keck telescopes , Mauna Kea ). The area of the primary mirror would have been larger than the area of all professional telescopes currently in operation combined. Even the secondary mirror would be overwhelmingly large with a diameter of 30 m. Both mirrors would not be made from one piece (which would not be technically feasible and would also be nonsensical because of the extremely high weight), but would be composed of hundreds of mirror segments. The main mirror should consist of 3048 hexagonal individual segments, the secondary mirror of 216 segments. In order to save costs, all segments of the main mirror should have the same curvature and together form a spherical instead of the usual parabolic or hyperbolic surface.
So should resolutions of only 0.001 arc seconds are possible. With an OWL one could observe stars up to the 38th magnitude (mag) . With the Hubble space telescope , observation up to 31 mag is possible - that is, with OWL you could still observe objects that are about 625 times weaker than with Hubble, or 625 trillion times weaker objects than with the naked eye under optimal viewing conditions.
construction
In contrast to previous large telescopes, the OWL should not be mounted under a dome, but should stand free itself and be protected during the day or in bad weather by an approximately 220 m large, self-supporting hall. This would have been moved aside for observations.
An important problem would be to keep the weight as low as possible through the use of new materials and designs, since the telescope has to be moved with the greatest precision. The tests assumed a total weight of 15,000 tons . For this purpose, 300 bogies with friction drives should be used, which run on circular tracks.
The planned optical structure consisted of a spherical primary mirror, a planar secondary mirror and a four-element catoptric corrector. The spherical primary mirror can be composed of uniform segments; the flat secondary mirror is comparatively insensitive to changes in position which are difficult to avoid given the size of the telescope. The corrector compensates for the spherical aberration of the primary mirror and contains the adaptive optics , which compensate for atmospheric disturbances of the incident light. The corrector would also have to compensate for the relatively strong deformation of the open mirror construction caused by wind.
The total costs were estimated at around 1.2 billion euros.
Location
Various locations were under discussion for the giant telescope , including the North Chilean Atacama Desert , where large telescopes such as B. the Very Large Telescope , or the Canary Islands, where the Gran Telescopio Canarias was completed in 2005 . A location near or in Antarctica was also considered after studies showed that the Dome C plateau, located at a latitude 75 degrees south at 3200 m above sea level, would be by far the cheapest place on earth for a telescope: very clean air , almost no stray light, little wind, drier climate than in the Sahara, thin air due to the altitude. These conditions come very close to a location in space. With a telescope of this size one strives to achieve optimal observation conditions according to as many criteria as possible. Locations as high as possible in very dry areas with the lowest possible seismic activity are therefore particularly suitable. The proximity to the sea is favorable because less disruptive air turbulence occurs there. In addition, the location should be as far away from larger metropolitan areas as possible in order to avoid interference from scattered light. Therefore z. B. Europe or the North American coasts are not considered from the outset, as they are far too densely populated. Accessibility plays a somewhat lesser role, as the astronomers no longer always have to travel in person for the observations. Highly qualified personnel on site, who know the complicated instruments very well, are more and more often performing the observations according to the applicant's instructions. The observation data are sent via the Internet or on data carriers.
outlook
A study of the OWL concept was completed and examined by a commission of experts in autumn 2005. While the validity of the concept was recognized, the Commission recommended instead a still very large telescope with 39 m primary mirror diameter, which ESO has been building since 2013 and recently renamed the Extremely Large Telescope , because of the risks to costs and timing . In this respect, a joking explanation of the abbreviation, in which OWL stands for "Originally was larger", has come true.
literature
- Giant telescope of the future in the spectrum of science , issue 08/2006
