A program for studying how objects move and interact under the force of gravity - Mac Shareware $79. AstroGrav is a software program that allows you to study how astronomical objects move and interact under the force of gravity. It features superb interactive 3D graphics which allow you to move around within an astronomical system that you are viewing, while watching how it evolves with the passage of time. A wide variety of sample files are provided, including Solar System, space mission, and abstract systems, and these enable you to experiment with AstroGrav without having to go to the trouble of entering your own data.

The comprehensive editing facilities allow you to either create your own astronomical systems, or to modify existing ones, and provide you with an almost endless scope for experimentation and investigation. AstroGrav calculates how astronomical objects move according to Newton's Law of Universal Gravitation, and displays the results as they are calculated so that you can watch the system evolve as in a movie. AstroGrav is very accurate, dynamically calculates orbits as a system evolves, deals correctly with object collisions, and can cope simultaneously with objects on many different timescales. AstroGrav is available for both Mac and Windows, comes complete with a tutorial and full documentation, and you can download a fully functional 15 day trial version for evaluation.