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Apoapsis An APSIS (Greek : ἁψίς; plural APSIDES /ˈæpsᵻdiːz/ , Greek: ἁψῖδες) is an extreme point in an object's orbit . The word comes via Latin from Greek and is cognate with apse . For elliptic orbits about a larger body, there are two apsides, named with the prefixes peri (from περί (peri), meaning 'near') and ap, or apo (from ἀπ(ό) (ap(ó)), meaning 'away from') added to a reference to the thing being orbited. * For a body orbiting the Sun Sun , the point of least distance is the PERIHELION (/ˌpɛrᵻˈhiːliən/ ), and the point of greatest distance is the APHELION (/æpˈhiːliən/ ) [...More...]  "Apoapsis" on: Wikipedia Yahoo 

Arithmetic Mean In mathematics and statistics , the ARITHMETIC MEAN ( /ˌærɪθˈmɛtɪk ˈmiːn/ , stress on third syllable of "arithmetic"), or simply the mean or AVERAGE when the context is clear, is the sum of a collection of numbers divided by the number of numbers in the collection. The collection is often a set of results of an experiment , or a set of results from a survey . The term "arithmetic mean" is preferred in some contexts in mathematics and statistics because it helps distinguish it from other means , such as the geometric mean and the harmonic mean . In addition to mathematics and statistics, the arithmetic mean is used frequently in fields such as economics, sociology , and history, and it is used in almost every academic field to some extent. For example, per capita income is the arithmetic average income of a nation's population [...More...]  "Arithmetic Mean" on: Wikipedia Yahoo 

Standard Gravitational Parameter In celestial mechanics , the STANDARD GRAVITATIONAL PARAMETER μ of a celestial body is the product of the gravitational constant G and the mass M of the body. = G M {displaystyle mu =GM } For several objects in the Solar System , the value of μ is known to greater accuracy than either G or M. The SI units of the standard gravitational parameter are m 3 s −2. However, units of km 3 s −2 are frequently used in the scientific literature and in spacecraft navigation. CONTENTS * 1 Small body orbiting a central body * 2 Two bodies orbiting each other * 3 Terminology and accuracy * 4 See also * 5 References SMALL BODY ORBITING A CENTRAL BODY The relation between properties of mass and their associated physical constants. Every massive object is believed to exhibit all five properties. However, due to extremely large or extremely small constants, it is generally impossible to verify more than two or three properties for any object [...More...]  "Standard Gravitational Parameter" on: Wikipedia Yahoo 

Geometric Mean In mathematics, the GEOMETRIC MEAN is a type of mean or average , which indicates the central tendency or typical value of a set of numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum). The geometric mean is defined as the nth root of the product of n numbers, i.e., for a set of numbers x1, x2, ..., xn, the geometric mean is defined as ( i = 1 n x i ) 1 n = x 1 x 2 x n n {displaystyle left(prod _{i=1}^{n}x_{i}right)^{frac {1}{n}}={sqrt{x_{1}x_{2}cdots x_{n}}}} For instance, the geometric mean of two numbers, say 2 and 8, is just the square root of their product, that is, 2 8 = 4 {displaystyle {sqrt {2cdot 8}}=4} . As another example, the geometric mean of the three numbers 4, 1, and 1/32 is the cube root of their product (1/8), which is 1/2, that is, 4 1 1 / 32 3 = 1 / 2 {displaystyle {sqrt{4cdot 1cdot 1/32}}=1/2} [...More...]  "Geometric Mean" on: Wikipedia Yahoo 

Semiminor Axis In geometry , the MAJOR AXIS of an ellipse is its longest diameter : a line segment that runs through the center and both foci , with ends at the widest points of the perimeter . The SEMIMAJOR AXIS is one half of the major axis, and thus runs from the centre, through a focus , and to the perimeter. Essentially, it is the radius of an orbit at the orbit's two most distant points. For the special case of a circle, the semimajor axis is the radius . One can think of the semimajor axis as an ellipse's long radius. The length of the semimajor axis a {displaystyle a} of an ellipse is related to the semiminor axis 's length b {displaystyle b} through the eccentricity e {displaystyle e} and the semilatus rectum {displaystyle ell } , as follows: b = a 1 e 2 , = a ( 1 e 2 ) , a = b 2 [...More...]  "Semiminor Axis" on: Wikipedia Yahoo 

Celestial Body An ASTRONOMICAL OBJECT or CELESTIAL OBJECT is a naturally occurring physical entity , association, or structure that current astronomy has demonstrated to exist in the observable universe . 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. A comet may be identified as both body and object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its diffuse coma and tail [...More...]  "Celestial Body" on: Wikipedia Yahoo 

Semimajor Axis In geometry , the major axis of an ellipse is its longest diameter : a line segment that runs through the center and both foci , with ends at the widest points of the perimeter . The SEMIMAJOR AXIS is one half of the major axis, and thus runs from the centre, through a focus , and to the perimeter. For the special case of a circle, the semimajor axis is the radius . The length of the semimajor axis a {displaystyle a} of an ellipse is related to the semiminor axis's length b {displaystyle b} through the eccentricity e {displaystyle e} and the semilatus rectum {displaystyle ell } , as follows: b = a 1 e 2 , = a ( 1 e 2 ) , a = b 2 . {displaystyle {begin{aligned}b&=a{sqrt {1e^{2}}},,\ell &=aleft(1e^{2}right),,\aell width:17.358ex; height:10.176ex;" alt="{displaystyle {begin{aligned}b&=a{sqrt {1e^{2}}},,\ell &=aleft(1e^{2}right),,\aell "> {displaystyle ell } fixed [...More...]  "Semimajor Axis" on: Wikipedia Yahoo 

Specific Orbital Energy In the gravitational twobody problem , the SPECIFIC ORBITAL ENERGY {displaystyle epsilon ,!} (or VISVIVA ENERGY) of two orbiting bodies is the constant sum of their mutual potential energy ( p {displaystyle epsilon _{p},!} ) and their total kinetic energy ( k {displaystyle epsilon _{k},!} ), divided by the reduced mass [...More...]  "Specific Orbital Energy" on: Wikipedia Yahoo 

Formula In science , a FORMULA is a concise way of expressing information symbolically, as in a mathematical or chemical formula . The informal use of the term FORMULA in science refers to the general construct of a relationship between given quantities . The plural of formula can be spelled either as formulas or formulae (from the original Latin). In mathematics , a formula is an entity constructed using the symbols and formation rules of a given logical language . For example, determining the volume of a sphere requires a significant amount of integral calculus or its geometrical analogue, the method of exhaustion ; but, having done this once in terms of some parameter (the radius for example), mathematicians have produced a formula to describe the volume: This particular formula is: V = 4 3 r 3 {displaystyle V={frac {4}{3}}pi r^{3}} . Having obtained this result, the volume of any sphere can be computed as long as its radius is known [...More...]  "Formula" on: Wikipedia Yahoo 

Kepler's Laws Of Planetary Motion In astronomy , KEPLER \'S LAWS OF PLANETARY MOTION are three scientific laws describing the motion of planets around the Sun . Figure 1: Illustration of Kepler's three laws with two planetary orbits. (1) The orbits are ellipses, with focal points ƒ1 and ƒ2 for the first planet and ƒ1 and ƒ3 for the second planet. The Sun is placed in focal point ƒ1. (2) The two shaded sectors A1 and A2 have the same surface area and the time for planet 1 to cover segment A1 is equal to the time to cover segment A2. (3) The total orbit times for planet 1 and planet 2 have a ratio a13/2 : a23/2 [...More...]  "Kepler's Laws Of Planetary Motion" on: Wikipedia Yahoo 

Angular Momentum In physics , ANGULAR MOMENTUM (rarely, MOMENT OF MOMENTUM or ROTATIONAL MOMENTUM) is the rotational analog of linear momentum . It is an important quantity in physics because it is a conserved quantity – the angular momentum of a system remains constant unless acted on by an external torque . The definition of angular momentum for a point particle is a pseudovector R×P, the cross product of the particle's position vector R (relative to some origin) and its momentum vector P = mV. This definition can be applied to each point in continua like solids or fluids, or physical fields . Unlike momentum, angular momentum does depend on where the origin is chosen, since the particle's position is measured from it [...More...]  "Angular Momentum" on: Wikipedia Yahoo 

Specific Relative Angular Momentum In celestial mechanics the SPECIFIC RELATIVE ANGULAR MOMENTUM h {displaystyle {vec {h}}} plays a pivotal role in the analysis of the twobody problem . One can show that it is a constant vector for a given orbit under ideal conditions. This essentially proves Kepler\'s second law . It's called specific angular momentum because it's not the actual angular momentum L {displaystyle {vec {L}}} , but the angular momentum per mass. Thus, the word "specific " in this term is short for "massspecific" or dividedbymass: h = L m {displaystyle {vec {h}}={frac {vec {L}}{m}}} Thus the SI unit is: m 2·s −1. m {displaystyle m} denotes the reduced mass 1 m = 1 m 1 + 1 m 2 {displaystyle {frac {1}{m}}={frac {1}{m_{1}}}+{frac {1}{m_{2}}}} [...More...]  "Specific Relative Angular Momentum" on: Wikipedia Yahoo 

Apollo Program The APOLLO PROGRAM, also known as PROJECT APOLLO, was the third United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA), which accomplished landing the first humans on the Moon from 1969 to 1972. First conceived during Dwight D. Eisenhower\'s administration as a threeman spacecraft to follow the oneman Project Mercury which put the first Americans in space, Apollo was later dedicated to President John F. Kennedy 's national goal of "landing a man on the Moon and returning him safely to the Earth" by the end of the 1960s, which he proposed in an address to Congress on May 25, 1961 [...More...]  "Apollo Program" on: Wikipedia Yahoo 

Artemis ARTEMIS (/ˈɑːrtᵻmᵻs/ ; Greek : Ἄρτεμις Artemis, Attic Greek : ) was one of the most widely venerated of the Ancient Greek deities. Her Roman equivalent is Diana . Some scholars believe that the name, and indeed the goddess herself, was originally preGreek. Homer Homer refers to her as Artemis Artemis Agrotera, Potnia Theron : " Artemis Artemis of the wildland, Mistress of Animals". The Arcadians believed she was the daughter of Demeter Demeter . In the classical period of Greek mythology Greek mythology , Artemis Artemis was often described as the daughter of Zeus Zeus and Leto , and the twin sister of Apollo Apollo [...More...]  "Artemis" on: Wikipedia Yahoo 

Ares ARES (/ˈɛəriːz/ ; Greek : Ἄρης ) is the Greek god of war . He is one of the Twelve Olympians Twelve Olympians , and the son of Zeus Zeus and Hera Hera . In Greek literature , he often represents the physical or violent and untamed aspect of war, in contrast to his sister the armored Athena Athena , whose functions as a goddess of intelligence include military strategy and generalship . The Greeks were ambivalent toward Ares: although he embodied the physical valor necessary for success in war, he was a dangerous force, "overwhelming, insatiable in battle, destructive, and manslaughtering." His sons Phobos (Fear) and Deimos (Terror) and his lover, or sister, Enyo (Discord) accompanied him on his war chariot . In the Iliad Iliad , his father Zeus Zeus tells him that he is the god most hateful to him [...More...]  "Ares" on: Wikipedia Yahoo 

Selene In Greek mythology , SELENE (/sᵻˈliːni/ ; Ancient Greek : Σελήνη 'moon ';) is the goddess of the moon. She is the daughter of the Titans Hyperion and Theia , and sister of the sungod Helios , and Eos , goddess of the dawn. She drives her moon chariot across the heavens. Several lovers are attributed to her in various myths, including Zeus , Pan , and the mortal Endymion . In classical times, Selene was often identified with Artemis , much as her brother, Helios, was identified with Apollo . Both Selene and Artemis were also associated with Hecate , and all three were regarded as lunar goddesses , although only Selene was regarded as the personification of the moon itself. Her Roman equivalent is Luna [...More...]  "Selene" on: Wikipedia Yahoo 