Читать книгу Geography For Dummies - Jerry T. Mitchell - Страница 66

People often say that Earth is a sphere. Not so. By definition, a sphere is a curved solid whose surface is always the same distance from its center, no matter at what point of the surface. Technically, Earth doesn’t fit that definition. Instead, Earth is an oblate spheroid, meaning it is somewhat flattened at its poles, or, if you prefer, it bulges somewhat around the Equator. The average distance from Earth’s center to the Equator is about 26 miles farther than the average distance from Earth’s center to the poles. Compared to the size of Earth, 26 miles isn’t a great distance, but it’s enough to make Earth not a real sphere. It’s better to say Earth is sphere-like, or an oblate spheroid.

Earth’s rotation causes its oblate-ness. The speed of Earth’s rotation is much faster at the Equator than near the Poles. This difference in speed may not be obvious, so think of it this way. Earth’s circumference measured along the Equator is about 25,000 miles. If you stand at a spot on the Equator for one day — for one full rotation — you’ll travel 25,000 miles. In contrast, if you stand a foot or two from the North Pole for one rotation, you’ll only travel a few yards. Obviously, somebody who travels 25,000 miles in one day is moving much faster than somebody who travels a few yards in the same time. So, the area near the Equator is spinning much faster than other parts of Earth. The outward, or centrifugal, force the high speed of rotation causes is so great that Earth bulges around the Equator as a result.

Maps of the world are among the most basic aids to geographic learning. Many people take it for granted that they are truthful. But in reality, all flat maps of the world lie — they simply cannot help it. If you’re new to thinking geographically, it is important that you appreciate that simple fact and understand the ways in which maps distort their portraits of your Earthly home. This chapter shows just how flat maps lie.