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The Advanced Cerro Paranal Sky Model

Sky background model

The physical model and software have been developed for ESO by a team of astronomers at the Institute for Astro- and Particle Physics at the University of Innsbruck, as one of three sky modeling and correction tools in an Austrian in-kind contribution to ESO.

SkyCalc Web Application

The web application SkyCalc provides a web interface to obtain models of transmission and radiance spectra in physical units, calculated on ESO servers with this model for configurable observation configurations and conditions.

Command-line interface (CLI)

A programmatic interface to SkyCalc skycalc_cli is available.

Source code

New! The source code of the skymodel is now available to download and install. Please see the documentation in the README.txt and the User Manual.


The document The Cerro Paranal Sky Model provides a guide to users who want to obtain detailed information on the basic structure and physical background of the skymodel. In addition to that, the document The Cerro Paranal Sky Model User Manual includes descriptions of the procedures for software installation and execution, the individual code segments (called modules) and the incorporated external software.

Disclaimer: The skymodel was developed for Cerro Paranal and an adaptation to other sites is not straightforward and may require significant user efforts. The assistance from ESO is restricted to the explanation of the site dependence of the different model components as given in the documentation, see section 9.3 in the User Manual. The code is released under GPL v.2 license "as is, under very limited support by ESO". The contact-point is

SM-01 Module 1 data library

As described in Section 4 of the User Manual, Module 1 of the SM-01 distribution can be used to compute libraries of spectra that are required for the software model to produce sky spectra. However, since this is very resource consuming, we have prepared some libraries that can be downloaded from the ESO FTP site. The file names indicate the types and resolution of the contained file sets. See section 4.2 in the User Manual for more details.


Telluric transmission spectra

A library of telluric transmission spectra with various resolutions and atmospheric conditions has been calculated with the Cerro Paranal sky model. A description of the usage of the spectra can be found in the article Moehler et al. (2014, A&A 568, A9).


In publications, users should refer to ESO (as the source of the skymodel code) and the related papers (Noll et al. 2012; Jones et al. 2013), see below.

(Noll et al. 2012) An atmospheric radiation model for Cerro Paranal. I. The optical spectral range
S. Noll, W. Kausch, M. Barden, A. M. Jones, C. Szyszka, S. Kimeswenger and J. Vinther

(Jones et al. 2013) An advanced scattered moonlight model for Cerro Paranal
A. Jones, S. Noll, W. Kausch, C. Szyszka and S. Kimeswenger

Known Issues


30. August 2018: First release of source code package v.1.0.0