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Interesting Facts About Earth
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■The name Earth originates from the 8th century Anglo-Saxon word erda, which means ground or soil. In Old English the word became eorthe, then erthe in Middle English. Earth was first used as the name of the sphere of the Earth around 1400. It is the only planet whose name in English is not derived from Greco-Roman mythology.
■In the ancient past there were varying levels of belief in a flat Earth, with the Mesopotamian culture portraying the world as a flat disk afloat in an ocean.
■Ozone layer together with Earth's magnetic field, blocks harmful radiation, permitting life on land.
■The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the conditions necessary to originate and sustain life on this planet.
■The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days).
■Outgassing and volcanic activity produced the primordial atmosphere of the Earth.
■Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans.
■The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later, the last common ancestor of all life existed.
■Earth has the highest density, the highest surface gravity and the strongest magnetic field and It is the largest of the four solar terrestrial planets, both in terms of size and mass.
■The magnetic field forms the magnetosphere, which deflects particles in the solar wind. The sunward edge of the bow shock is located at about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the Van Allen radiation belts, a pair of concentric, torus-shaped regions of energetic charged particles. When the plasma enters the Earth's atmosphere at the magnetic poles, it forms the aurora.
■on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of the Earth averages about 30 km/s (108,000 km/h), which is fast enough to cover the planet's diameter (about 12,600 km) in seven minutes, and the distance to the Moon (384,000 km) in four hours.
■The angle of the Earth's tilt is relatively stable over long periods of time. However, the tilt does undergo a slight, irregular motion (known as nutation) with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge.
■The Hill sphere (gravitational sphere of influence) of the Earth is about 1.5 Gm (or 1,500,000 kilometers) in radius. This is maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.
■In total, about 400 people have been outside the Earth's atmosphere as of 2004, and, of these, twelve have walked on the Moon. Normally the only humans in space are those on the International Space Station. The station's crew of three people is usually replaced every six months.
■Earth was first photographed from space by Explorer 6 in 1959.
■Yuri Gagarin became the first human to view Earth from space in 1961.
■The crew of the Apollo 8 was the first to view an Earth-rise from lunar orbit in 1968. In 1972 the crew of the Apollo 17 produced the famous "Blue Marble" photograph of the planet Earth from cislunar space(the most widely distributed image in human history).
Source: Wikipedia - NASA
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