Could you prove to me how one might calculate things like mass, gravity, distance, of the sun, moon and Earth, very quickly, with only some basic knowledge. Such as 365.25 per year, min, avg and max times for the moon to complete a lunar phase 29.26,29.53,29.8). I'm attempting to understand how ancient people may have found those answers. But I'd like to know the best methods, to figure out older possible methods more quickly. If you don't know what I'm getting at with the included estimates, 29.26/29.8= 0.98187, a close estimate of Earth's gravity. While it's easy enough to see the relationship with a few calculations, I'd want to understand how to make the calculation without having read gravity is 9.807 m/s^2. And to build on that understanding, for other calculations.