Copyrights and licensing

While the calculations and plots produced by are intended to be useful and reliable, they come with no guarantee of any kind. All risk arising from the use of this website and the data it provides is borne by the user. If you find any errors in the calculations, or wish to contact me for any other reason about, please get in touch at

The source code for is copyright © Roger Wesson 2018—. The site uses a list of observatories originally from astropy-data/coordinates, which is under a BSD license.

The header image was taken by me at La Silla. It is freely available under a Creative Commons license, as are many of my photographs of ESO sites.

Note about data usage

When you use, various items of data are recorded by the server. These logs are retained for three days and then deleted. By inspecting the server logs, I can see the details of the observability charts that have been generated - the object name and coordinates, the location of the observer, the date and time. I use these data to improve the website - for example, I have added new observatory locations when user-defined locations or geolocated positions have shown that users are at an astronomical observatory that was not in the database. No user data is transferred to any third party at any time.