Mary Nielsen, age 11, of Houston, Texas, for her question
What is the shape of the Solar System?
The general shape of the Solar System is somewhat like an oval platter. However, its outer edges are far from trim. that's more, we need on the spot investigations to determine the outer limits of the solar family. Experts, however, have definite measurements of the inner picture of the disk.
Our Solar System is but a cluster of dusty motes in the teeming universe. Yet it is a neat and orderly family and astronomers assure us that no major changes can be expected in the next few billion years. Its basic structure is a slightly oval disk wheeling around its central starry sun. The sun is an immense ball of incandescent gases and its seething nuclear powerhouse contains all but a fraction of one per cent of all the material in the entire Solar System. The other major members of the system are the nine planets. Their or¬bital paths around the sun sketch in the general outline of the system.
The planetary orbits are more or less on a level with the sun's equator. However, some are more sharply tilted to this plane and some are more circular than others. Pluto, the ninth planet, travels the longest and the most. elliptical or oval shaped path. At times the little outside planet comes within the orbit of Neptune, the eighth planet. At other times the distance between it and Neptune is greater than the distance between any of the other planetary orbits. Pluto's orbit also is tipped the most sharply to the plane of the sun's equator.
The planetary frame work of the system can be scaled down to understandable dimensions. Suppose we teduce the sun to .a two foot wide beach ball. The earth would be a pea sized planet traveling a fairly circular orbit 430 feet wide, while Pluto would be merely the size of a pinhead, traveling an elliptical path 3 1/4 miles long and 3 miles wide. If our model is on the open prairie, the tilted orbit of Pluto would swoop up above the grass.
The diameter of the Solar System can be estimated from the orbit of the little odd ball outer planet. Pluto's average distance from the sun is roughl~ .3,600 million miles. This makes the average width of the major disk system about 7,200 million earth miles. The dis¬tance can also be clocked by the travel time of light. Sunlight from the sun takes 500 seconds to reach the earth, about four hours to reach Neptune and almost seven hours to Pluto when it is farthest...from the sun. In light time, the width of the main structures varies from four to seven hours. Out beyond Pluto there are clouds of orbiting meteors. They add a fuzzy extension to the mainzttructure and we are not certain how far they reach. Moons and comets, asteroids and other space traveling meteors also populate the spacious regions between the planets.
The sun rotates on its axis towards the east direction and so do the major planets. All the planets also orbit around the sun in this direction. Most of the moons of the Solar System also rotate and orbit their planet parents in this same direction. So do most of the swarming asteroids. But the razzle dazzle comets disregard this general traffic rule of the Solar System. About half of those studied pursue their long oval paths in step with the planets. The other half travel westward in a contrary direction.