Earth

Earth is the densest, fifth largest, and third closest planet to the sun in the solar system. It is the place of origin and home of all known living things. Its diameter is more than 12,700 kilometers and its age is about 4.6 billion years. According to its predominant geochemical composition, the term "Earth-like planets" was coined. The astronomical symbol of the Earth is or .

Since the Earth's surface consists of about two-thirds water and therefore the Earth appears predominantly blue when viewed from space, it is also called the Blue Planet. It is also metaphorically referred to as "Spaceship Earth".

The earth as the basis of human life plays a prominent role in all religions as a sacred whole; in several ethnic, folk and historical religions either as the deification of a "Mother Earth" or as a personified earth goddess.

Etymology

The Common Germanic noun earth in Middle High German, in Old High German erda, is based on er- with related words of other Indo-European languages.

Orbit

According to Kepler's first law, the Earth moves in an elliptical orbit around the Sun. The sun is located in one of the foci of the ellipse. The major axis of the ellipse connects the point farthest from the Sun and the point closest to the Sun in the orbit. The two points are called aphelion and perihelion. The mean of the aphelion and perihelion distance is the length of the major semi-major axis of the ellipse and is about 149.6 million km. This length originally defined the astronomical unit (AU), which is the astronomical unit of length used mainly for distances within the solar system.

The aphelion is 1.017 AU (152.1 million km) and the perihelion is 0.983 AU (147.1 million km). Thus, the ellipse has an eccentricity of 0.0167. The aphelion transit occurs around July 5 and the perihelion transit occurs around January 3. The Earth orbits the Sun in 365 days, 6 hours, 9 minutes, and 9.54 seconds; this period is also called the sidereal year. The sidereal year is 20 minutes and 24 seconds longer than the tropical year on which the civil year of calendar reckoning is based. The Earth's orbital velocity is 29.78 km/s on average, 30.29 km/s at perihelion, and 29.29 km/s at aphelion; thus, the Earth covers a distance the length of its diameter in just over seven minutes.

Earth's orbit is distant from Venus' inner neighboring orbit by an average of 0.28 AU (41.44 million km) and from Mars' outer neighboring orbit by an average of 0.52 AU (78.32 million km). However, Mercury is closest to Earth on average (1.039 AU). There are several coorbital objects in Earth's orbit, for more details see: Earth's orbit.

The Earth orbits the Sun prograde, that is, in the direction of the Sun's rotation, which is counterclockwise as viewed from the north pole of the Earth's orbital plane.

The Earth's orbital plane is called the ecliptic. The ecliptic is inclined by a good 7° to the equatorial plane of the sun. The north pole of the sun faces the earth most strongly towards the beginning of September, the south pole of the sun towards the beginning of March. The earth is in the sun's equatorial plane only briefly around June 6 and December 8.