The term Adaptive Optics (AO) indicates systems that correct distortions from the Atmosphere using input from a sensor that measures the distortion. Typically, the sensor tracks the distortion (e.g., slight mislocation) of a known fixed source, e.g., a star or even the light reflected from a laser used to provide a source. The source light must be near the line-of-site to the object under observation. The same distortion presumably affects objects in that area of the Celestial Sphere, including the observation target.

Some current and planned telescopes using adaptive optics:

• Keck Observatory
• European Extremely Large Telescope (E-ELT)
• Giant Magellan Telescope (GMT)
• Thirty Meter Telescope (TMT)

Multi-Conjugate AO is adaptive optics that is specifically designed to correct for distortion at multiple distances from the telescope.