Adding an “artificial” star to the multitude in the sky

Below the trails left by the stars in a dark and clear night, a laser beam shoots out of Yepun, the fourth Unit Telescope of Europe’s flagship observatory, ESO’s Very Large Telescope (VLT). This beam is used to create an artificial star above Paranal to assist the adaptive optics instruments on the VLT. 

Adaptive optics is a technique that allows astronomers to overcome the blurring effect of the atmosphere and obtain images almost as sharp as would be possible if the whole telescope were placed in space, above Earth's atmosphere.