European Extremely Large Telescope

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European Extremely Large Telescope (E-ELT)
Not yet build Not yet built
Organization:	ESO
Location:	Probably Chile
Wavelength:	Optical, near infrared
Built:	Planned completion: 2017
Telescope style:	Reflector
Diameter:	42m
Angular resolution:	0.001 to 0.6 arcseconds depending on target and instruments used
Focal length:	420-840 m (f/10 - f/20)
Mounting:	Alt/az
Dome:	Spherical
Website:	http://www.eso.org/projects/e-elt/

The European Extremely Large Telescope (E-ELT) is an extremely large telescope design proposed for the next-generation European Southern Observatory optical telescope with a mirror diameter of 42 meters. ESO is focusing on this design after a feasibility study concluded that the proposed 100m diameter Overwhelmingly Large Telescope would cost €1.5 billion (£1 billion), and be too complex.

Current fabrication technology limits single mirrors to being roughly 8 meters in a single piece. The next-largest telescopes currently in use are the Gran Telescopio Canarias and Southern African Large Telescope, which each use hexagonal mirrors fitted together to make a mirror more than 10 meters across. The ELT would need to use a similar design. In addition, ELT would also need to use techniques to work around atmospheric distortion of incoming light, known as adaptive optics.

Project ELT has the aim of observing the Universe in greater detail than even the Hubble Space Telescope. A mirror of approximately 42 meters would allow the study of the atmospheres of extrasolar planets. The 5-mirror anastigmat design is estimated to cost €800 million and could be completed by 2017[1].