Size and Distance in the Solar System

(This 881st Buffalo Sunday News column was first published on February 10, 2008.)

Whenever I stand on the shore of one of our Great Lakes I find myself deeply moved by how small and insignificant I am. Sailing in mid-ocean when I was a naval officer gave me an even greater sense of this proportion. I could look in any direction and see nothing but a seeming infinitude of waves against the ever receding skyline.

(Despite this, you are not always alone out there. One day I heard our deck officer call out, "Hard right rudder," certainly a non-standard instruction in mid-Atlantic. Everyone rushed topside to see what looked like a floating mine bump past our ship's side. Thankfully, it wasn't a mine. Instead it was one of those buoys carried by cargo ships that unreel to float above a sunken ship. At sea the depth was too great and the buoy had simply floated off. If that had been a mine, I would not be writing this column.)

These and other size comparisons are found on the website, The Size of Our World.

The planets between Earth and Pluto are Venus, Mars and Mercury.

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If those expanses on Earth are impressive, they are nothing to those of space. Heavens indeed. And it's not just us. Our entire planet is tiny in our solar system, to say nothing of the universe.

Teachers use a variety of ways to demonstrate these distances to their students. Bob Doyle, columnist for the Cumberland (MD) Times-Union, tells how he has students use a string about a yard long. A big knot at one end represents the sun and knots representing the planets at various points along the string show their relative distance from the center of the solar system. He then uses different kinds of fruit to show how some of the planets compare in size.

I wanted to approach this in a different way. I sought a way of combining the size of the planets and sun with the planetary distances from the sun in the same scheme. An impressive website titled Build a Solar System, developed by Ron Hipschman of San Francisco's Exploratorium, helped me to do this. It allows you to work from a size you choose for the sun to determine the corresponding size of each planet as well as its average distance from the sun.

It took a bit of trial and error before I hit upon a reasonable size to choose for the sun. It seems to me that we are better able to understand these size comparisons if we start from where we are. I wanted to begin with a size for the earth and work from there. With a bit of arithmetic I could then get the sun size and use Hipschman's values.

What should I choose for the size of the earth? I thought of several possibilities -- a baseball? a softball? a beach ball? These created representation problems. Finally, I hit upon what worked best for me, something we are all familiar with: a ping pong ball.

A ping pong ball has a well defined diameter: 40 millimeters or about 1.5748 inches. If we convert the earth to that size, we must shrink its diameter by a factor of almost 322 million. Quite a squeeze but it gives us a basis for comparison.

Okay, now the earth is the size of a table tennis ball. Here are the comparisons. The sun is then a bit over 14 feet in diameter, big enough to fill a high ceiling school classroom. The planets are far smaller. Next in size are Jupiter and Saturn, about 17 and 14 inches in diameter -- beach ball sized. Then Uranus and Neptune, their diameters each a bit under 6 inches, like grapefruit. Venus, at 1.5 inch diameter, is only slightly smaller than the earth. The smallest planets (now that Pluto is no longer among them) are Mars at .8 inches and Mercury at .6 inches, each grape-sized.

Now the orbital distances: Our ping pong ball is about 500 yards (five football fields) from the sun. Closer are Mercury, 200 yards and Venus, 400 yards. Our near partner Mars is a bit under 800 yards, about a half mile. The other planets are miles away: Jupiter 1.5, Saturn 2.8, Uranus 5.6 and distant Neptune 8.8 miles.

Even so severely reduced in size those distances are awfully large. We are indeed infinitesimally tiny objects in a boundless space.-- Gerry Rising