By Orbital Team
Starlight arriving at a ground based telescope has already passed through several kilometers of turbulent atmosphere, and that turbulence bends the light in ways that change many times per second. Without correction, this is what causes stars to twinkle and blurs fine detail out of any image taken from the ground.
Adaptive optics systems correct for this in real time using a deformable mirror, a thin reflective surface backed by dozens or hundreds of actuators that physically flex the mirror's shape hundreds of times per second to cancel out atmospheric distortion as it happens.
To know exactly how to deform the mirror, the system needs a reference point of known shape. Bright stars work when one happens to sit near the target, but for most of the sky observatories now fire a powerful laser to excite sodium atoms in the upper atmosphere, creating an artificial guide star exactly where it is needed.
The result on the best equipped ground telescopes now approaches, and in some infrared wavelengths exceeds, the resolution of space based observatories, at a fraction of the cost of a launch and with the option to swap instruments on the ground.
Space telescopes still win decisively at wavelengths the atmosphere blocks entirely, such as most of the ultraviolet and far infrared. But for visible and near infrared work, adaptive optics has turned ground based astronomy from a fundamentally blurrier alternative into a genuine competitor.