Introduction

These pages are on the borderline between hard Science Fiction and genuine science. In the hard SF tradition, everything here is scientifically rigorous, except when it is more fun to bend the rules. The pages have 3 aims:

To help people understand the general physics of stellar and planetary systems. Speculation is rife about alien worlds circling alien suns, but many are unrealistic because the effects of the universal laws governing them are not appreciated. People design worlds from science fiction, anthropological and role-playing perspectives. Some are happy not to worry about such details, but others might appreciate the verisimilitude a few calculations can bring.
To help with those calculations. Few are complicated, but they are tedious to perform, and there is no central reference with them all (if you know better, I'd love to know).
To look how other people have prepared their worlds.

Forms allow you to select a pair of starting points from a set of both real stars and planets and those from Science Fiction. It is possible to design your own worlds. The Sun-Earth-Moon combination can always be chosen for comparison.

There are details of the scientific ideas behind the program and the available systems.

Acknowledgements

Thanks to all the people in SDS, Contact and the Contact Consortium who have sparked my interest in this field, and especially Melanie Harper, who used to host the site for many years, and Alex McLintock, who hosts it now.