License
Everything on this site is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0): the text, the prepared figures, the calculator and the sheets it prints. You may copy, adapt, redistribute and sell it. The only condition is that the source is named.
The license took effect on 26 August 2026 and cannot be revoked: whatever has been passed on under it stays free. That is the point, not a side effect — a school that puts the printout on its intranet should not have to ask again two years from now.
How to credit
One line is enough:
truedistance.org by Niels Hegmans, CC BY 4.0
Online, please include both links — to the site and to the license:
<a href="https://www.truedistance.org/">truedistance.org</a> by Niels Hegmans, <a href="https://creativecommons.org/licenses/by/4.0/">CC BY 4.0</a>On a printed sheet the line is already in the footer, so passing it on unchanged needs nothing further. If you change it, say so (“adapted from …”). That is all CC BY asks for: no permission, no fee, and no obligation to license your own work the same way.
What is not included
A license can only give away what is mine. Three things on this site are not, or not in that way:
- The typefaces. IBM Plex Sans and IBM Plex Mono are IBM’s and carry the SIL Open Font License 1.1. They may travel with the files, but under their own license, not this one.
- The name “truedistance” and the mark (the Sun with a planet on its orbit). CC BY explicitly does not cover trademark rights. Take the content, take the numbers — but do not build something that looks like it is this site.
- Linked third-party sites. Whatever they say applies there.
The data was free already
Body data come from JPL Horizons (NASA/JPL, public domain), the ring measurements from the PDS Ring-Moon Systems Node, the stars from the Bright Star Catalogue (Hoffleit & Warren, Yale University Observatory, public domain). Facts are not copyrightable in the first place; what is licensed here is their presentation.
The same goes for the starry background on the printed sheets: it is not a photograph but drawn from 8,418 catalogue positions, point by point out of public-domain coordinates. No third party holds a picture right in it.
The source code is separate
The code behind this site is under the MIT license, not CC BY. That is not a caveat but Creative Commons’ own advice: their licenses say nothing about source code, linking or patents, which is why they recommend against using them for software. In short: reuse text, figures or sheets under CC BY 4.0; reuse the calculation code under MIT.
For schools, museums and adult education
Print it, copy it for the class, put it on the school network or into Moodle, translate it, fold it into your own material, hand it out at a training day: all allowed, no request, no fee. If something good comes of it I would love to hear about it — the address is in the imprint. That is a wish, not a condition.