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FIGURE 16.1 Artist’s concept of the relative size and order of the eight planets of the solar system (not to scale).

northward. This established that Earth’s surface was curved, at
least, which seemed to fit with other evidence.
The shape and size of Earth have been precisely mea sured
by artificial satellites circling Earth. These measurements have
found that Earth is not a perfectly round sphere as believed by the
ancient Greeks. It is flattened at the poles and has an equatorial
bulge, as do many other planets. In fact, you can observe through
a telescope that both Jupiter and Saturn are considerably flattened

Direction
of the Sun's
motion in
space

Earth's motion
relative to space
FIGURE 16.3 Earth as seen from space.

at the poles. A shape that is flattened at the poles has a greater
Earth's orbit distance through the equator than through the poles, which is
around the Sun described as an oblate shape. Earth, like a water-filled, round bal-
loon resting on a table, has an oblate shape. It is not perfectly sym-
FIGURE 16.2 Earth undergoes many different motions as it
metrically oblate, however, since the North Pole is slightly higher
moves through space. There are seven more conspicuous motions,
three of which are more obvious on the surface. Earth follows the and the South Pole is slightly lower than the average surface. In
path of a gigantic helix, moving at fantastic speeds as it follows the addition, it is not perfectly circular around the equator, with a
Sun and the galaxy through space. lump in the Pacific and a depression in the Indian Oceans. The

16-3 CHAPTER 16 Earth in Space 407