Guide Star

High above Paranal Mountain in Atacama Desert of Chile, of the four VLT telescopes is using Laser Guide Star Facility. The yellow light is a laser guide star for Adaptive Optics (AO), a technology to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion, most commonly used to remove the effects of atmospheric distortion. AO systems require a wavefront reference source in order to correct atmospheric distortion and because bright stars are not available in all parts of the sky, the system shine a laser into the atmosphere to create a yellow artificial “star” in the 95 km altitude sodium cloud around the Earth. As noted by the photographer “Exposure time for this photograph was 40 minutes on a fixed tripod. One can see rotation both around North and South poles while the trails of the stars at the celestial equator are straight lines”.