If I Were to Build a Model of the Cosmos... 

Let's try to build a scale model of the universe. The visible sun has a diameter of 864,000 miles (more than 3/4 million miles). Let us build a model universe in which the sun is reduced in size to a sphere one millimeter in diameter (about the size of a salt grain). On this scale, Earth would be as large as a single grain of talcum powder (10 microns), and would be 4.3 inches from the sun. On the same scale, Proxima Centauri would still be 17 miles away. If a sphere, with a radius of 17 miles, were constructed around our scale model sun, there would be one star on the sphere's surface, Proxima Centauri. All the remaining stars of the galaxy would be located outside the sphere. The Milky Way galaxy would have a scale diameter of 425,000 miles, i.e., almost twice the actual distance from the earth to the moon. M31 would be slightly larger than the Milky Way (500,000 miles or so in diameter), and would be located 7,000,000 miles away, more than 1/10 the distance from the earth to Mars at opposition (Mars' point of closest approach to the earth)!

And so on, outward ...