Adaptive optics Guide, Meaning , Facts, Information and Description
Adaptive optics is a technology to improve the performance of reflecting telescopes by reducing the effects of twinkling. Adaptive optics work by rapidly "adapting" and reshaping telescopic mirrors. The technique was only practical starting in the 1990s due to advances in computer technology. Adaptive optics should not be confused with active optics, which works on a longer timescale to correct the mirror geometry itself.Adaptive optics technology has also been used recently to image individual cone photoreceptors in the living, human eye. See here.
When light from a star or another astronomical object enters the Earth's atmosphere, the different temperature layers and different wind speeds distort and move the image in various ways (see astronomical seeing for a proper discussion). The net result is that an 8 meter or 10 meter telescope (like the VLT or Keck), while theoretically capable of milli-arcsecond resolution, is limited to what the atmosphere permits, which can easily be a factor of 50 or 100 worse.
An adaptive optics system tries to correct these distortions, using a quality-of-image detector, a deformable mirror, and a computer that receives input from the detector and calculates the optimal deformation of the mirror.
This is possible only because the theoretical, perfect image is known in advance: in the case of a point-like star, the image is a circle with certain characteristics dictated by the telescope's aperture.
The necessity of a reference star means that an adaptive optics system cannot work everywhere on the sky, but only where 'guide stars' of sufficient luminosity (for current systems, about magnitude 11-12) can be found very near to the object of the observation.
An alternative is the use of a laser beam to generate a beacon in the atmosphere, to act as a guide star - referred to as a laser guide star).
Other approaches that can yield resolving power exceeding the limits of atmospheric seeing include Lucky Imaging and space telescope such as NASA's Hubble Space Telescope
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