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Surface Gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in order not to disturb the system, has negligible mass. Surface gravity is measured in units of acceleration, which, in the SI system, are meters per second squared
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Astronomical Object
An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the observable universe.[1] In astronomy, the terms "object" and "body" are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, that may consist of multiple bodies or even other objects with substructures. Examples for astronomical objects include planetary systems, star clusters, nebulae and galaxies, while asteroids, moons, planets, and stars are astronomical bodies
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Eris (dwarf Planet)
Eris (minor-planet designation 136199 Eris) is the most massive and second-largest dwarf planet known in the Solar System. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. In September 2006 it was named after Eris, the Greek goddess of strife. Eris is the ninth most massive object directly orbiting the Sun, and the 16th most massive overall, because seven moons are more massive than all known dwarf planets. It is also the largest which has not yet been visited by a spacecraft. Eris was measured to be 2,326 ± 12 kilometers (1,445.3 ± 7.5 mi) in diameter.[8] Eris's mass is about 0.27% of the Earth
Earth
mass,[10][16] about 27% more than dwarf planet Pluto, although Pluto
Pluto
is slightly larger by volume.[17] Eris is a trans-Neptunian object (TNO) and a member of a high-eccentricity population known as the scattered disk
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Newtonian Gravity
Newton's law of universal gravitation
Newton's law of universal gravitation
states that a particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.[note 1] This is a general physical law derived from empirical observations by what Isaac Newton called inductive reasoning.[1] It is a part of classical mechanics and was formulated in Newton's work Philosophiæ Naturalis Principia Mathematica ("the Principia"), first published on 5 July 1686. When Newton's book was presented in 1686 to the Royal Society, Robert Hooke
Robert Hooke
made a claim that Newton had obtained the inverse square law from him. In today's language, the law states: Every point mass attracts every single other point mass by a force pointing along the line intersecting both points
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Gravity
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including objects ranging from atoms and photons, to planets and stars. Since energy and mass are equivalent, all forms of energy (including light) cause gravitation and are under the influence of it. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe
Universe
caused it to begin coalescing, forming stars – and for the stars to group together into galaxies – so gravity is responsible for many of the large scale structures in the Universe
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Gravitational Force
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including objects ranging from atoms and photons, to planets and stars. Since energy and mass are equivalent, all forms of energy (including light) cause gravitation and are under the influence of it. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe
Universe
caused it to begin coalescing, forming stars – and for the stars to group together into galaxies – so gravity is responsible for many of the large scale structures in the Universe
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Gravitational Acceleration
In physics, gravitational acceleration is the acceleration on an object caused by the force of gravitation. Neglecting friction such as air resistance, all small bodies accelerate in a gravitational field at the same rate relative to the center of mass.[1] This equality is true regardless of the masses or compositions of the bodies. At different points on Earth, objects fall with an acceleration between 7000976399999999999♠9.764 m/s2 and 7000983400000000000♠9.834 m/s2[2] depending on altitude and latitude, with a conventional standard value of exactly 9.80665 m/s2 (approximately 32.174 ft/s2)
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Inverse Square Law
The inverse-square law, in physics, is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity. The fundamental cause for this can be understood as geometric dilution corresponding to point-source radiation into three-dimensional space (see diagram). Radar
Radar
energy expands during both the signal transmission and also on the reflected return, so the inverse square for both paths means that the radar will receive energy according to the inverse fourth power of the range. In order to prevent dilution of energy while propagating a signal
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Light
Light
Light
is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).[2][3] This wavelength means a frequency range of roughly 430–750 terahertz (THz).Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli Fantina, SicilyThe main source of light on Earth
Earth
is the Sun. Sunlight
Sunlight
provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them
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Planet
Shown in order from the Sun
Sun
and in true color. Sizes are not to scale.A planet is an astronomical body orbiting a star or stellar remnant thatis massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a][1][2]The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System
Solar System
can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union
International Astronomical Union
(IAU) officially adopted a resolution defining planets within the Solar System
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Hydrostatic Equilibrium
In fluid mechanics, a fluid is said to be in hydrostatic equilibrium or hydrostatic balance when it is at rest, or when the flow velocity at each point is constant over time. This occurs when external forces such as gravity are balanced by a pressure gradient force.[1] For instance, the pressure-gradient force prevents gravity from collapsing Earth's atmosphere into a thin, dense shell, whereas gravity prevents the pressure gradient force from diffusing the atmosphere into space. Hydrostatic equilibrium
Hydrostatic equilibrium
is the current distinguishing criterion between dwarf planets and small Solar System
Solar System
bodies, and has other roles in astrophysics and planetary geology. This qualification typically means that the object is symmetrically rounded into a spheroid or ellipsoid shape, where any irregular surface features are due to a relatively thin solid crust
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Gravitational Potential Energy
Gravitational energy
Gravitational energy
is the potential energy a body with mass has in relation to another massive object due to gravity. It is potential energy associated with the gravitational field. Gravitational energy is dependent on the masses of two bodies, their distance apart and the gravitational constant (G).[1] In everyday cases only one body is accelerating measurably, and its acceleration is constant (for example, dropping a ball on Earth)
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Sphere
A sphere (from Greek σφαῖρα — sphaira, "globe, ball"[1]) is a perfectly round geometrical object in three-dimensional space that is the surface of a completely round ball (viz., analogous to a circular object in two dimensions). Like a circle, which geometrically is an object in two-dimensional space, a sphere is defined mathematically as the set of points that are all at the same distance r from a given point, but in three-dimensional space.[2] This distance r is the radius of the ball, and the given point is the center of the mathematical ball
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Azimuth
An azimuth (/ˈæzɪməθ/ ( listen)) (from the pl. form of the Arabic noun "السَّمْت" as-samt, meaning "the direction") is an angular measurement in a spherical coordinate system. The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth. An example of azimuth is the angular direction of a star in the sky. The star is the point of interest, the reference plane is the local horizontal area (e.g. a circular area 5 km in radius around an observer at sea level), and the reference vector points north. The azimuth is the angle between the north vector and the star's vector on the horizontal plane.[1] Azimuth
Azimuth
is usually measured in degrees (°)
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Equatorial Bulge
An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the force exerted by its rotation. A rotating body tends to form an oblate spheroid rather than a sphere. The Earth
Earth
has an equatorial bulge of 42.77 km (26.58 mi); that is, its diameter measured across the equatorial plane (12,756.27 km (7,926.38 mi)) is 42.77 km more than that measured between the poles (12,713.56 km (7,899.84 mi)). An observer standing at sea level on either pole, therefore, is 21.36 km closer to Earth's centrepoint than if standing at sea level on the equator. The value of Earth's radius may be approximated by the average of these radii. An often-cited result of Earth's equatorial bulge is that the highest point on Earth, measured from the center outwards, is the peak of Mount Chimborazo in Ecuador, rather than Mount Everest
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67P/Churyumov–Gerasimenko
67P/Churyumov–Gerasimenko
67P/Churyumov–Gerasimenko
(abbreviated as 67P or 67P/C-G) is a Jupiter-family comet,[7] originally from the Kuiper belt,[8] with a current orbital period of 6.45 years,[1] a rotation period of approximately 12.4 hours[6] and a maximum velocity of 135,000 km/h (38 km/s; 84,000 mph).[9] Churyumov–Gerasimenko is approximately 4.3 by 4.1 km (2.7 by 2.5 mi) at its longest and widest dimensions.[10] It was first observed on photographic plates in 1969 by Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, after whom it is named
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