SIMBAD references

An all-sky cloud-monitoring system that generates relative opacity maps over many of the world's premier astronomical observatories is described. Photometric measurements of numerous background stars are combined with simultaneous sky brightness measurements to differentiate thin clouds from sky glow sources such as airglow and zodiacal light. The system takes a continuous pipeline of all-sky images and compares them to canonical images taken on other nights at the same sidereal time. Data interpolation then yields transmission maps covering almost the entire sky. An implementation of this system is currently operating through the Night Sky Live network of CONCAM3s located at Cerro Pachón (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT (South Africa), and the Canary Islands (Northwestern Africa).