Firing the laser

Two 8.2-m Unit telescopes of ESO's VLT are seen. To the right, Yepun, Unit Telescope number 4 fires its laser which creates an artificial reference star, which is used to measure and correct for the blurring caused by the local atmosphere so that the deformable mirror of the telescope can correct for it. Thanks to these laser guide stars, almost the entire sky can now be observed with the technique known as adaptive optics.