Brad Lewis, age 13, of Des Moines, Iowa, for his question:
How far is the sun from the different planets?
The orbits of the nine planets are slightly oval ellipses, which means that their distances from the sun vary. Astronomers, however, have kindly calculated these variations to give us a convenient average distance between the sun and each of its planets. On this basis, the distances range from 36 million miles to 3,670 million miles.
The positions of the different planets give us a pretty good picture of the Solar System but it is a rather large picture for our minds to grasp. Perhaps we should start with a model scaled down to understandable dimensions.
The planetary orbits are more or less level with the sun's equator. Though some are slightly tilted to this plane, we can use a fairly flat field for our model. On the scale we have chosen, the earth is represented by a pea and the stretch of level ground is three miles wide and three and a quarter miles long.
Our model sun is scaled down to the size of a beach ball, placed almost but not quite in the center of the field. Its distance from Mercury, its closest planet, is 82 feet and little Mercury is represented by a tiny grain of mustard seed. Next is Venus, represented by a pea at a distance of 142 feet.
The third planet from the sun is our gorgeous Earth. On our scaled down model, it is represented by a pea placed at a distance of 215 feet from the sun. Mars, the fourth planet, is represented by a large pinhead on an orbit that averages 327 feet from the sun.
The extra large space between Mars and Jupiter is occupied by swarms of asteroids, the four largest are specks of dust, orbiting our model sun at distances ranging from 1,000 to 1,200 feet. Giant Jupiter is modeled by a medium sized orange and the distance between it and our beach ball sun is almost a quarter of a mile. Saturn becomes a small orange at a distance of about 2,112 feet from the model sun.
Uranus, the size of a small plum, is placed at about three quarters of a mile from the model sun. Neptune becomes a slightly smaller plum separated from the model sun by one and a quarter miles. Little Pluto, which usually occupies the outside orbit, shrinks to the size of a pea. The distance between our model sun and its oval orbit ranges from a mile and a half to a mile and five eighths.
We can translate this mini model into the vast dimensions of the Solar System, which spans almost 8,000 million miles from side to side. In millions of miles, the distance between the sun and Mercury is about 36; Venus, 67; the earth 93; Mars, 141; Jupiter, 483; Saturn, about 886.
The average distance of the sun from Uranus is 1,783 million miles and from Neptune it is 2,793 million miles. Along part of its yearly orbit, Pluto comes inside the orbit of Neptune but its average distance from the sun is 3,673 million miles. This means that Pluto, the outside planet, is about 39 tines farther from the sun than is the planet Earth.