Earth Earth Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. It is the largest of the solar system's terrestrial planets, and the only planetary body that modern science confirms as harboring life. Scientific evidence indicates that the planet formed around 4.57 billion (4.57 ) years ago, and shortly thereafter (4.533 billion years ago) acquired its single natural satellite, the Moon. ...more on Wikipedia about "Earth"
* The International Committee co-ordinates funds and control between the nations of the Earth of the Stargate. Under it's auspices the Atlantis mission of major nations (notably Britain, the USA, Canada, Germany and Russia) was sent to the Pegasus Galaxy ...more on Wikipedia about "Earth in fiction"
The radius of Earth (or any planet) is the distance from its centre to a point on its surface at mean sea level. Like most planets, Earth is not a perfect sphere, but instead is somewhat flattened at the North and South Poles, and bulges at the equator, which means that its radius and corresponding radius of curvature, or arcradius, differs depending on where you measure it (and, in the case of the arcradius, even which direction is being faced!). This elliptic shape is known as an oblate spheroid/ellipsoid. ...more on Wikipedia about "Earth radius"
The Earth can be considered as a physical system with an energy budget that includes all gains of incoming energy and all losses of outgoing energy. The planet is approximately in equilibrium, so the sum of the gains should be approximately equal to the sum of the losses. ...more on Wikipedia about "Earth's energy budget"
Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the geographic north pole and the other near the geographic south pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3° from the planet's axis of rotation. The cause of the field is probably explained by dynamo theory. The magnetic field extends several tens of thousands of kilometres into space as the magnetosphere. ...more on Wikipedia about "Earth's magnetic field"
An Earth-crosser asteroid is a Near-Earth asteroid whose orbit crosses that of Earth. The known numbered Earth-crossers are listed here. Buried in the list is one peculiar asteroid: 3753 Cruithne, whose orbit enjoys an unusual special relationship with Earth's. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. See also the Amor asteroids. ...more on Wikipedia about "Earth-crosser asteroid"
In telecommunication, effective Earth radius is the radius of a hypothetical Earth for which the distance to the radio horizon, assuming rectilinear propagation, is the same as that for the actual Earth with an assumed uniform vertical gradient of atmospheric refractive index. ...more on Wikipedia about "Effective Earth radius" shortopedia - Go in quickly.
The notion of a Flat Earth refers to the idea that the inhabited surface of Earth is flat, rather than curved (see Spherical Earth). ...more on Wikipedia about "Flat Earth"
A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earth's magnetic field. Unlike reversals however, an excursion does not change the large scale orientation of the field, but rather represents a dramatic, typically short-lived decrease in field intensity. These events, which typically last a few thousand to a few tens of thousands of years, often involve declines in field strength to between 0-20% of normal. ...more on Wikipedia about "Geomagnetic excursion"
A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events, which typically last a few hundred to a few thousands years, often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established. ...more on Wikipedia about "Geomagnetic reversal"
A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere. Associated with solar coronal mass ejections (CME), coronal holes, or solar flares, a geomagnetic storm is caused by a solar wind shock wave which typically stikes the Earth's magnetic field 24 to 36 hours after the event. This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. These solar wind pressure changes modify the electric currents in the ionosphere. Magnetic storms usually last 24 to 48 hours, but some may last for many days. ...more on Wikipedia about "Geomagnetic storm"
The phrase hollow earth refers to the esoteric idea that the planet Earth has a hollow interior, almost always associated with the idea that it has a habitable inner surface. Although at one time adventure literature made this idea popular and even commonplace, the notion now receives little support; substantial geodetic evidence has long controverted it and the scientific community dismisses it as pseudoscience. ...more on Wikipedia about "Hollow Earth"
The mediocrity principle is the notion in the philosophy of science that there is nothing special about Earth, and by implication the human race. It is a Copernican principle, used either as a heuristic about Earth's position or a philosophical statement about the place of humanity. ...more on Wikipedia about "Mediocrity principle"
The oldest known object on Earth is a tiny speck of zircon crystal. It is the oldest known piece of Earth at about 4.4 billion years old. Researchers in 2001 discovered that the early Earth was much cooler than previously believed based on analysis of this crystal. ...more on Wikipedia about "Oldest known object on Earth"
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Precession refers to a change in the direction of the axis of a rotating object. In physics, there are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail. In certain contexts, "precession" may refer to the precession that the Earth experiences, the effects of this type of precession on astronomical observation, or to the precession of orbital objects. ...more on Wikipedia about "Precession"
The rare Earth hypothesis is a response to the Fermi paradox which explains why we might expect a planet such as Earth to be very rare. Combined with the additional assumption that an Earth-like planet is a prerequisite for the development of advanced life, this offers an explanation for the current lack of evidence of extraterrestrial civilizations. ...more on Wikipedia about "Rare Earth hypothesis"
The South Atlantic Anomaly (or SAA) is the region where Earth's inner van Allen radiation belt makes its closest approach to the planet's surface. The result is that, for a given altitude, the radiation intensity is higher over this region than elsewhere. The SAA is produced by a "dip" in the Earth's magnetic field at that location, caused by the fact that the center of Earth's magnetic field is offset from its geographic center by 450 kilometers (280 miles). During Operation Argus nuclear warheads were detonated at high altitudes in the SAA to research the possibility of destroying incoming ICBMs; this did not work at all. ...more on Wikipedia about "South Atlantic Anomaly"
The idea of a spherical Earth was espoused by Pythagoras apparently on aesthetic grounds, as he also held all other celestial bodies to be spherical. ...more on Wikipedia about "Spherical Earth"
The Earth's structure is the geologic and atmospheric structure of earth. ...more on Wikipedia about "Structure of the Earth"
The subsolar point on earth is where the sun is perceived to be directly overhead. ...more on Wikipedia about "Subsolar"
"The Blue Marble" is a famous photograph of the Earth taken on 7 December 1972 by the crew of the Apollo 17 spacecraft at a distance of about 45,000 kilometers or about 28,000 miles. ** . It is one of the most widely distributed photographic images in existence. Earth is said to have the appearance of a child's marble in the photo; that is the Earth has the same aspect at this distance as a child's marble at about arm's length. ...more on Wikipedia about "The Blue Marble" You've Got Questions. We've Got shortopedia.
The Van Allen radiation belt is a torus of energetic charged particles (ie. a plasma) around Earth, trapped by Earth's magnetic field. When the belts "overload", particles strike the upper atmosphere and fluoresce, causing the polar aurora. The presence of a radiation belt had been theorized prior to the Space Age and the belt's presence was confirmed by the Explorer I on January 31, 1958 and Explorer III missions, under Doctor James Van Allen. The trapped radiation was first mapped out by Explorer IV and Pioneer III. ...more on Wikipedia about "Van Allen radiation belt"
The volume of the Earth is, in cubic meters, around 1.0832×1021 m3, which is 1,083,200,000,000,000,000,000 m3 written in scientific notation. ...more on Wikipedia about "Volume of the Earth"
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