In the current era of precision astronomy, a complete sky background model is crucial, especially as the telescopes become even larger in the next decade. Such a model is needed for planning observations as well as understanding and correcting the data for the sky background. We have developed a sky model for this purpose, and it is the most complete and universal sky background model that we know of to date (Article A). It covers a wide range of wavelengths from 0.3 to 30 microns up to a resolution of 1,000,000 and is instrument independent. Currently it is optimized for the telescopes at Cerro Paranal and the future site Cerro Armazones in Chile. Its original purpose was to improve the ESO (European Southern Observatory) ETC (Exposure Time Calculator) used for predicting exposure times of observations with a given signal to noise ratio for a set of conditions, as part of the Austrian contribution to ESO. Improving the ETC allows for better scheduling and telescope efficiency, and our new sky model has already been implemented by ESO.
The brightest natural source of optical light at night is the Moon, and it is a major contributor to the astronomical sky background. We have an improved scattered moonlight model (Article B and G), where all of the components are computed with physical processes or observational data with less empirical parametrizations. This model is spectroscopic from 0.3 to 2.5 microns and was studied and verified with observations. To our knowledge, this is the first spectroscopic model extending into the near-infrared.
There are several applications of the sky background model. We have developed two tools for data reduction, skycorr (Article C) and molecfit (Article E and F). Additionally, the sky background model can be used in atmospheric science. Since the model is more physical, we can use the scattered moonlight to determine the distribution of aerosols (Article D). We can also investigate airglow.