Page:The Music of the Spheres.djvu/241

 centrifugal force to offset the gravitational pull, and the closer the planet the faster it must fly. Mercury, for instance, travels at a rate of 35 miles a second while Neptune, seventy-five times as far off, has an orbital velocity of only 3.4 miles a second. The following table shows the distances of each planet from the sun and the time it takes it to complete its journey around its orbit, beginning with Mercury, the nearest planet to the sun, and continuing outward.

Mercury, Venus, Earth and Mars are sometimes called the inner planets because they form a group nearest the sun but more