Creating artificial stars at the VLT

Adaptive optics employed by the Very Large Telescope at ESO's Paranal Observatory correct for distortions introduced by the Earth's atmosphere. However to function, adaptive optics requires a fairly bright reference star close to the object of study which naturally is not always possible. To mitigate this issue, astronomers can create artificial stars instead by shining a powerful laser beam into the Earth's upper atmosphere. These laser guide stars allow almost the entire visible sky to be observed with adaptive optics.