Laser by starlight
Laser tracking helps astronomers the star behind the twinkle.
Adaptive optics (AO) measures and then corrects the atmospheric turbulence using a deformable mirror that changes shape 1,000 times per second.
Initially, AO relied on the light of a star that was both bright and close to the target celestial object. But there are only enough bright stars to allow AO correction in about one percent of the sky.
In response, astronomers developed Laser Guide Star Adaptive Optics using a special-purpose laser to excite sodium atoms that sit in an atmospheric layer 60 miles above Earth. Exciting the atoms in the sodium layers creates an artificial "star" for measuring atmospheric distortions which allows the AO to produce sharp images of celestial objects positioned nearly anywhere in the sky.
The image above shows a laser guide beam in action at the Keck Observatory in Hawai'i.