Mountaintop telescope

Even from far away, the laser guide star on Unit Telescope 4 (Yepun) of ESO's Very Large Telescope (VLT) can be seen lighting up the night sky as it helps take observations. The VLT is located at the top of Cerro Paranal, a 2600-metre high mountain in the Chilean Atacama Desert. This site was chosen largely for the excellent viewing conditions it offers to astronomers, with about 300 clear nights per year. No matter the conditions, however, there are still atmospheric effects that can interfere with the light reaching Earth from elsewhere in the Universe. The VLT is therefore kitted out with an Adaptive Optics system, state-of-the-art technology that corrects the blurring effects of Earth's atmosphere. The laser plays a central role in this system, by creating an artificial star that can be used to deduce the specific atmospheric effects that the light is subject to.