A two-dimensional Java gravity simulation featuring the Earth, the Moon, Venus (in ultraviolet light) and Mars.
The relative body sizes and masses are correct but their distances apart are much less than in reality. On this scale, the Earth and Moon should be around a metre apart, with Venus and Mars thousands of screen widths away!
Any one body at a time can be grabbed and dragged with the mouse. The buttons along the top allow you to hold or resume motion of the bodies; switch on and off the background music and collision 'gongs'; change the value of 'G' (the 'strength' of gravity) and hide or show each of the bodies (if a body is 'hidden' it has no effect gravitationally).
Click on the image above to start the simulation (this will take several seconds if downloading via the internet).