European
Southern
Observatory

Telescope
Adaptive Optics

The turbulence of the Earth's atmosphere distorts images obtained at even the best sites in the world for astronomy, including Chile's Cerro Armazones, home to the ELT.

The telescope will employ incredibly sophisticated 'adaptive optics' technologies to ensure its images are sharper than those of any other telescope.

In a nutshell

The telescope will employ incredibly sophisticated 'adaptive optics' technologies to ensure its images are sharper than those of any other telescope.

The turbulence of the Earth's atmosphere distorts images obtained at even the best sites in the world for astronomy, including Chile's Cerro Armazones, home to the ELT.

The telescope will employ incredibly sophisticated 'adaptive optics' technologies to ensure its images are sharper than those of any other telescope.

Turbulence in the Earth’s atmosphere causes the stars to twinkle in a way that delights poets but frustrates astronomers since it blurs the finest details of the cosmos. Observing directly from space can avoid this atmospheric blurring effect, but the high costs of operating space telescopes compared to using ground-based facilities limits the size and scope of the telescopes we can place off-Earth. 

Astronomers have turned to a method called adaptive optics. Sophisticated, deformable mirrors controlled by computers can correct in real-time for the distortion caused by the turbulence of the Earth's atmosphere, making the images obtained almost as sharp as (or, in the case of the ELT, sharper than) those taken in space. Adaptive optics allows the corrected optical system to observe finer details of much fainter astronomical objects than is otherwise possible from the ground.

This illustration aims to show how the nebula NGC 3603 could be seen by three different telescopes: the NASA/ESA Hubble Space Telescope, ESO’s Very Large Telescope with the help of its adaptive optics modules, and the Extremely Large Telescope. Credit: ESO

Adaptive optics requires a fairly bright reference star that is very close to the object under study. This reference star is used to measure the blurring caused by the local atmosphere so that the deformable mirror can correct for it. Since suitable stars are not available everywhere in the night sky, astronomers can create artificial stars instead by shining a powerful laser beam into the Earth's upper atmosphere. Thanks to these laser guide stars, almost the entire sky can now be observed with adaptive optics. The ELT will have up to eight of these lasers.

From the largest adaptive mirror ever built to advanced control systems, the ELT will have some of the most sophisticated technologies ever employed on a telescope to correct for the blurring effects of the Earth’s atmosphere. This page, currently under construction, will explore those technologies.

This video explains the principles of adaptive optics, a technique used in many ESO telescopes. Credit: ESO