Earth. Size and movements

Earth is our home, a beautiful and diverse planet. It is the third planet from the Sun in our solar system and is composed of a unique combination of elements and conditions that allow the existence of life as we know it. It is the densest and fifth largest of the eight planets in the solar system. It is also the largest of the four terrestrial or rocky planets. Earth is home to an astonishing diversity of ecosystems and living things, from microorganisms to animals and plants. In addition to terrestrial life, the oceans are home to a variety of marine creatures, from tiny fish to majestic whales and fascinating coral reefs.

The shape of the Earth is described as a geoid, meaning that it has a shape similar to a sphere that is slightly flattened at the poles and widened at the equator. This is due to the effect of the Earth’s rotation, which generates a slight bulge at the equator due to centrifugal force. The equatorial radius is 6,378 kilometers (3,963 miles) while the polar radius is 6,357 kilometers (3,950 miles).

Composition of the Earth

The Earth’s surface is mostly (71%) covered by oceans of water. The remainder is made up of continents and islands. The Earth’s poles are mostly covered with solid ice. No other planet is known with this amount of liquid water, which is indispensable for any known type of life. The interior of the planet is geologically active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid inner core composed of about 88 % iron. The Earth is covered by a layer of air called the atmosphere, which protects and maintains conditions suitable for life. This atmosphere is composed mainly of nitrogen and oxygen.

Earth’s motion

The Earth performs several motions, the most important of which are rotation and translation.

Rotation. The Earth rotates on its imaginary axis in a west-to-east motion. This complete rotational motion is carried out in approximately 24 hours, resulting in the succession of days and nights. The Earth’s rotation is responsible for the daily cycle of the sun and for the patterns of light and dark in different regions of the planet.

Translation. The Earth performs a translational motion around the Sun. It takes approximately 365.25 days (one year) to complete one orbit around the Sun. This translational motion is responsible for the seasons of the year. As the Earth moves around the Sun.

Other motions of the Earth are precession, nutation, Chandler’s wobble and perihelion precession.