Laser Guide Star in Paranal

The night sky is full of stars, but there are other astronomical objects visible in this picture taken at Paranal Observatory. The pinkish nebula at the very bottom on the left is the Carina nebula. Further up, there is a bluish bright star: it is Canopus, the second-brightest star in the night sky. Over to the right of Canopus, the two bluish clouds of the Large and Small Magellanic Clouds, two irregular neighbouring galaxies of the Milky Way, can be seen. To observe these and other celestial objects in greater detail, the biggest barrier for ground-based telescopes is the turbulence of Earth’s atmosphere, which makes astronomical images blurry. But the ESO’s Very Large Telescope’s (VLT) adaptive-optics system can solve this issue, and the lasers of the Laser Guide Stars Facility installed on the VLT’s Unit Telescope 4 play a key role. These lasers excite the sodium atoms in the atmosphere, which in turn emit light that is affected by the irregular air motions in the same way as the light from stars. The light is collected by the telescope and can be used by the VLT’s adaptive-optics system to measure the distortions introduced by the atmosphere and then to correct for them.