شكل الأرض – المراجع العلمية

ENCYCLOPEDIA BRITANNICA

The fifth largest planet of the solar system, the Earth has an equatorial circumference of 40.076 km (24.902 miles), an equatorial radius of 6.378 km (3.963 miles), a polar radius of 6.357 km (3.950 miles), and a mean radius of 6.371 km (3.960 miles). The planet’s total surface area is roughly 509.600.000 square km (197.000.000 square miles), of which about 29 percent, or 148.000.000 square km (57.000.000 square miles), is land. The balance of the surface is covered by the oceans and smaller seas. The Earth has a mass of 5.976 × 10²⁷ grams (or roughly 6 × 10²¹ metric tons) and a mean density of 5.517 grams per cubic cm (0.2 pound per cubic inch).

The centrifugal force of the Earth’s rotation makes the planet bulge at the Equator. Because of this, the Earth has the shape of an oblate spheroid, being flatter near the poles than near the Equator. Correspondingly, one degree of latitude is longer in high latitudes than it is in low ones.