ESO Exposure Time Calculators
Note: These tools are only provided for technical assessment of observation feasibility. Variations of the atmospheric conditions can strongly affect the required observation time. Calculated exposure time does not take into account instrument and telescope overheads. Users are advised to exert caution in the interpretation of the results and to report any result which may appear inconsistent.
Please consult the Frequently Asked Questions page for problem solving and additional information.
Faster execution: As of March 4th 2005, the ETC system has been migrated to a Linux server, which
has improved the performance by approximately 5x and up to 8x in some cases.
The average response time of the application is now 2 seconds for the imaging and 5 seconds for spectroscopy. Actual computation time may vary depending on the load of the machine.
Transmission accuracies have been tested for the existing instruments and are in the range 5-20 % for imaging and 10-30 % for spectroscopy. Transmissions for the instruments are based on available engineering data.
In optical spectroscopy, atmospheric emission lines are only taken into account in the domain 650-920 nm. The sky signal is assumed constant with wavelength out of this range.