How can a telescope correct the atmosphere’s blur?

Light from a distant star would reach a telescope in a nearly flat wavefront if it traveled through an undisturbed path. Earth’s atmosphere contains moving regions with different refractive properties. They delay different parts of the light by different amounts, changing the wavefront and blurring the image.

Adaptive optics measures these changing distortions using light from a reference star or an artificial guide source. A wavefront sensor supplies information about the incoming shape. A controller estimates a compensating pattern and sends commands to actuators behind a deformable mirror.

Small changes in the mirror’s surface change the distances traveled by reflected light. A suitable pattern can reduce the measured wavefront error before light forms the science image. Because the atmosphere keeps changing, the measurement and correction repeat rapidly.

This is different from making one blurry photograph sharper afterward: the optical path itself is being adjusted during observation. Correction is still imperfect and applies over a limited region. It also differs from active optics, which primarily corrects slower changes in the telescope’s own large optical structure.