Twinkle Twinkle Little Star
Some stars gently twinkle in the night sky as the Earth’s turbulent atmosphere causes their light to shimmer. This causes problems for astronomers, who want the crispest possible views. To help them achieve this, a laser guide star is used to create an artificial star 90 km above the surface of the Earth. The laser energises sodium atoms high in the Earth’s mesosphere, causing them to glow and creating a bright dot that to observers on the ground appears to be a man-made star.
Observations of how this “star” twinkles are fed into the Very Large Telescope’s adaptive optics system, controlling a deformable mirror in the telescope to restore the image of the star to a sharp point. By doing this, the system also compensates for the distorting effect of the atmosphere in the region around the artificial star. The end result is an exceptionally crisp view of the sky, allowing astronomers to make stunning observations of the Universe, almost as though the VLT were above the atmosphere in space.