Astronomers observe light from stars many light years away and yet the thin atmosphere that surrounds Earth can play havoc with their results. Small volumes of the atmosphere have different temperatures and densities; they move around and this turbulence causes incoming light to change direction. The change in direction shows up as distortions in the data and can either render measurements useless or make their interpretation difficult. Observatories are often built on high mountains to limit the thickness of atmosphere the light needs to travel through. However, for the most detailed projects the thinnest atmosphere is still enough to cause problems.
U.S. astronomer Horace Babcock (1912-2003) devised an optical system in 1953 that could adapt to the changes and correct the errors in real time. Although his design gave hope to toiling astronomers, it was not used until the 1990s when computers could keep up with the speed of the fast changing atmosphere.
The technique is called adaptive optics and works by measuring the incoming distortion and quickly sending this information to deform a mirror. The incoming light from a star is reflected from the deformed mirror and measured as what it would have been without an atmosphere. The computer must be able to analyze the information about the changing atmosphere and send signals to the mirror to change its shape many times in a second. Implementing the technique has been difficult—materials for the bendable mirror and computing power have held the technology back, but when successful it has made massive improvements to the quality of images.
