According to The Hitchhiker's Guide to the Galaxy, "Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. . . . . The simple truth is that interstellar distances will not fit into the human imagination." (Chapter 8)

What is needed is a good scale model of the solar system to show relationships between the sizes of the planets and the distances between them.

First, we will start the the actual distances between the sun and planets and the actual sizes of the planets. We will include some other items, such as the sizes of various stars and the distance light travels in a year (light year). Note that the planetary radius of the Moon is based on its distance from the Earth, while that of the planets is based on the distance from the Sun.

Actual Distances and Sizes

Notice that some of these distances, like the distance to the Galactic center, are shown in scientific notation, simply because the number 162,901,000,000,000,000 is rather clumsy to write and even clumsier to comprehend.

In most scale models of the solar system, either the size of the planets is compared or their distances from the Sun, but usually not both at the same time. The reason for this can be seen from a comparison of the planetary diameters and the planetary radii. The numbers for planetary radii are on the order of one thousand times the size of the numbers for planetary diameters, so the scale of distances is about a thousand times the scale of sizes. We will attempt to pick a scale which will compare both and still keep things somewhat in perspective.

Now we decide on a scale. For this, we will start with the Earth being 1 inch in diameter and scale the entire solar system to that.

Scaled Distances and Sizes

As you can see from the chart, even when we pick a reasonable size for the earth, the size of the solar system is still quite large. On our scale, with the earth being about the size of a big marble, the earth is about 325 yards away, about three city blocks. Pluto is about seven and a half miles, about a brisk two and a half hour walk away. That's a BIG neighborhood. And the nearest star: that's more than twice around the earth! The average driver in the United States takes 5 years to put that much mileage on a car.

This scale is roughly 1 to 500 million. At various places around the world other scale models have been set up. In Gainsville, Florida a model has been constructed on a 1 to 4 billion scale that extends over nine-tenths of a mile, and in Maine a model on the scale of 1 to 93 million covers 40 miles. Eugene, Oregon has a 6 km model and Ithaca, New York has one that is dedicated to Caral Sagan that covers 1.2 km. Other countries have scale models also. One only has to check around to find them.

This is our little corner of the block. Yet if we look at the local neighborhood, the Milky Way galaxy, the system breaks down. Our galaxy is about 100,000 light-years across, 2,000 light years thick, and we are roughly 26,000 light years from the center. That means that, on our scale of the earth being one inch in diameter, the Milky Way galaxy is 1,172,000,000 miles across, 23,500,000 miles thick, and we are roughly 305,000,000 from the center. As far as the distance to Andromeda Galaxy, even on the scale model the distance is ridiculously large.

It seems that scale models, although very useful in many applications, are not a very useful astronomer's tool except in limited cases. As was stated earlier, distances can be compared to distances, sizes can be compared to sizes, but scale models such as this that compare both size and distance on the same scale are useful only on a very limited basis. Truly, space is very mind-bogglingly huge.

(A sidenote here: This is NOT a finished article. It may be some time before I finish it to my own satisfaction. If you wish a METRIC version, let me know. I just might be persuaded to whip one up.) LL&P, RtC