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# Topic: Semimajor axis

###### In the News (Mon 20 May 13)

 Semi-major axis - Wikipedia, the free encyclopedia The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape. The semi-major axis is one half of the major axis, and thus runs from the centre, through a focus, and to the edge of the ellipse. It is often said that the semi-major axis is the "average" distance between the primary (the focus of the ellipse) and the orbiting body. en.wikipedia.org /wiki/Semimajor_axis   (690 words)

 Ellipse - Wikipedia, the free encyclopedia A semimajor axis is one half the major axis: the line segment from the center, through a focus, and to the edge of the ellipse. The constant a equals the length of the semimajor axis; the constant b equals the length of the semiminor axis. The shape of an ellipse is usually expressed by a number called the eccentricity of the ellipse, conventionally denoted e (not to be confused with the mathematical constant e). en.wikipedia.org /wiki/Ellipse   (1106 words)

 Semimajor Axis a planetary orbit) is 1/2 the length of the major axis which is a segment of a line passing thru the foci of the ellipse with endpoints on the ellipse itself. The semimajor axis of a planetary orbit is also the average distance from the planet to its primary. The semi-major axis of an orbital ellipse is one of the "orbital elements" characterizing it, and is directly related to the energy of the motion. www.websters-online-dictionary.org /se/semimajor+axis.html   (352 words)

 NSRT Reference: The Planets   (Site not responding. Last check: 2007-10-21) The semimajor axis is basically the distance from the planet to the Sun. Technically, the semimajor axis is the longer axis of an ellipse. The equatorial inclination to the orbit is the tilt of the rotation axis. astrwww.astr.cwru.edu /Reference/planets.html   (1882 words)

 Semi-major axis - Wikipedia, the free encyclopedia   (Site not responding. Last check: 2007-10-21) In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. It is related to the semi-minor axis $bthrough theeccentricityeand the semi-latus rectuml, as follows:$ $a\,is the length of theorbit\text{'}ssemi-major$axis www.bucyrus.us /project/wikipedia/index.php/Semi-major_axis   (853 words)

 Kepler's Laws (Lab 3) First Law The long axis of the ellipse is called the major axis, while the short axis is called the minor axis. The length of the semimajor axis is often termed the radius of the ellipse. Thus, by the "radius" of a planet's orbit one usually means the length of the semimajor axis. www.unm.edu /~astro1/101lab/lab3/lab3_A.html   (355 words)

 axis axis -- (the main stem or central part about which plant organs or plant parts such as branches are arranged) 4. axis, axis vertebra -- (the 2nd cervical vertebra; serves as a pivot for turning the head) Overview of noun axis The noun axis has 5 senses (first 2 from tagged texts) 1. axis, axis vertebra -- (the 2nd cervical vertebra; serves as a pivot for turning the head) www.beetfoundation.com /words/a/alt.axis.html   (233 words)

 Mapping Fundamentals (Mapping Toolbox)   (Site not responding. Last check: 2007-10-21) The semimajor axis can be in any unit of distance; the choice of these units often drives the units used for distance outputs in the toolbox functions. When compared to the semimajor axis, which is almost 6400 kilometers, this difference seems insignificant and can be neglected for most purposes. The difference between the semimajor and semiminor axes of a correct ellipse at this scale would be far smaller than the width of the line used to draw it. www.haystack.edu /computing/matlab6.5/help/toolbox/map/fundm112.html   (684 words)

 Ellipse : Semimajor axis   (Site not responding. Last check: 2007-10-21) The line which passes through the foci is the major axis and also the longest line which passes through the ellipse. The line which passes through the centre (halfway between the foci), at right angles to the major axis, is the minor axis. It uses material from the wikipedia article Ellipse : Semimajor axis. www.eurofreehost.com /se/Semimajor_axis.html   (326 words)

 semi-major axis Half the longest distance (major axis) across an ellipse. The semi-major axis is one of the orbital elements — a standard parameter used to describe an elliptical orbit. The semimajor axis is also the average distance of an orbiting object from its primary. www.daviddarling.info /encyclopedia/S/semimajor.html   (135 words)

 Racist Celestial Mechanics, Lecture 1: Orbital Elements to Heliocentric State Vectors   (Site not responding. Last check: 2007-10-21) For elliptical orbits, the semimajor axis is the distance from the center of the ellipse to either of the "long ends" of the ellipse. For hyperbolic orbits, the semimajor axis is the distance from the vertex (the point where the hyperbolic asymptotes cross) and the nearest point on the hyperbolic curve. The distance from the vertex to the perihelion is, by definition, the semimajor axis of the hyperbolic orbit. www.jabpage.org /posts/trans1.html   (4181 words)

 Parameters Describing Elliptical Orbits The angle from the ascending node to the pericenter, measured in the plane of the orbit. a is the length of the semimajor axis and and a is the semimajor axis of the orbit, also measured in AU (which has a negative value for hyperbolic orbits). www.lns.cornell.edu /~seb/celestia/orbital-parameters.html   (714 words)

 [No title]   (Site not responding. Last check: 2007-10-21) If the user wishes to supply constants for a spheroid other than those in Table 3, a negative spheroid code must be used, and the semimajor axis and semiminor axis or eccentricity squared must be supplied in the input and output projection constants. The values of the semimajor axis, semiminor axis, the radius of the sphere, the height of the perspective center, the false easting, and the false northing must be expressed in meters. axis or radius of the sphere --------+------------------------------------------------- geography.usgs.gov /ftp/software/current_software/gctp/l176-um.txt   (1809 words)

 Origins of Modern Astronomy   (Site not responding. Last check: 2007-10-21) A convenient unit of measurement for periods is in Earth years, and a convenient unit of measurement for distances is the average separation of the Earth from the Sun, which is termed an astronomical unit and is abbreviated as AU. As an example of using Kepler's 3rd Law, let's calculate the "radius" of the orbit of Mars (that is, the length of the semimajor axis of the orbit) from the orbital period. Thus, by Kepler's 3rd Law the length of the semimajor axis for the Martian orbit is www.d.umn.edu /~hmooers/astro/Origins_of_Modern_Astronomy.htm   (439 words)

 Semimajor axis   (Site not responding. Last check: 2007-10-21) The semimajor axis (also semi-major axis) is one half of the major axis of an ellipse, running from the center, through a focus, and to the edge of the ellipse. In astronomy, the semimajor axis is one of the most important characteristics of an orbit, along with its period. For solar system objects, the semimajor axis is related to the period of the orbit by Kepler's Third Law (originally empirically derived), www.sciencedaily.com /encyclopedia/semimajor_axis   (277 words)

 Satellite Speed at Extremes   (Site not responding. Last check: 2007-10-21) The eccentricity e=.25 is the ratio of the distance from the center to a focus of the elliptical orbit, cf, to the length of the semimajor axis, a, of the orbit. The semimajor axis, a, is also the sum of the perihelion and cf. The total energy of the satellite in elliptical is -G*M*m/2*a where G is the universal gravitation constant, M is the mass of the Earth, m is the mass of the satellite and a is the semimajor axis of the orbit. www.mcasco.com /qa_ssae.html   (241 words)

 IMAP   (Site not responding. Last check: 2007-10-21) The first element is the axis minimum, and the second is the axis maximum. The default is the semimajor axis length of either the Clarke 1866 datum (6378206.4 meters) or the Sphere radius (6370997.0 meters), depending on the projection. The default is the semiminor axis length of either the Clarke 1866 datum (6356583.8 meters) or the Sphere radius (6370997.0 meters), depending on the projection. idlastro.gsfc.nasa.gov /idl_html_help/I12.html   (3735 words)

 GLOSSARY.DOC - Semi-Major Axis   (Site not responding. Last check: 2007-10-21) If the orbit is a circle, the semi-major axis is the radius of the circle. If it is an ellipse, the major axis is the longest diameter, while the minor axis is the shortest. These points (the foci) are not centered in the ellipse, so the semi-major axis does not directly describe the altitude at perigee. www.sat-net.com /winorbit/help/kepsemimajoraxis.html   (106 words)

 Section 2: The Motion of Comets The geometrical constants which fully define the shape of the ellipse are the semimajor axis a and the eccentricity e (see Figure 2 currently not available). The semiminor axis b is related to those two quantities by the equation b = a(1-e^2). In the first paragraph of this section, it was stated that the geometric constants of an ellipse are its semimajor axis and eccentricity. www.seds.org /sl9/Educator/section02.html   (1027 words)

 [No title] Note that for small semimajor axis the limiting perihelion distance is 35 AU (in good corespondence with numerical works, e.g. One can roughly estimate their Lyapunov time from the magic formula: T_lyap = sqrt(32/3)*a_res / (da * k) (in time units of an orbital period), where a_res is the resonant semimajor axis, da is the resonant width and k is integer in front of small bodies mean longitude in the resonant angle (i.e. If there is no large difference between osculating and mean semimajor axes, the nominal orbit of 1995 TL8 seems to indicate that this is a scattered disk object which sticked to 3N:7 and decreased eccentricity. www.boulder.swri.edu /~davidn/kbmmr/kbmmr.html   (828 words)

 Orbit Simulator   (Site not responding. Last check: 2007-10-21) The square of a body's orbital period is proportional to the cube of the semimajor axis of its orbit. The semimajor axis refers to the size of the orbit. where P is the orbital period, a is the semimajor axis of the orbiting body, and K is a proportionality constant. observe.arc.nasa.gov /nasa/education/referance/orbits/orbit_sim.old.html   (265 words)

 Crossroads in Mathematics Revise your model in part A using the earth's period and semimajor axis as the units of time and distance. Predict Pluto's orbit period given that its semimajor axis is 5.9 billion km. Part A. Because each x represents a semimajor axis, the points corresponding to the four inner planets are closely clustered, just as the planets themselves are closely clustered in the solar system. www.imacc.org /standards/ex12.html   (918 words)

 axis The term is also applied for the axis of a graph; the horizontal axis x-axis, the vertical y-axis and the z-axis is a possible third axis used for three-dimensional graphing. In anatomy, the axis (C2) is the second cervical vertebra of the spine. When talking about the Axis (capitalised), usually the alliance of Germany, Italy and Japan in World War II is meant (see Axis Powers). www.fact-library.com /axis.html   (212 words)

 An Introduction to the Large Scale, fall 2000-2001, Homework 4   (Site not responding. Last check: 2007-10-21) The value of the constant depends, of course, on the UNITS used to measure the period and the semimajor axis. You should travel along an elliptical orbit where the end closest to the sun (the perihelion) is tangent to the orbit of Earth, and the end furthest from the sun (the aphelion) is tangent to the orbit of Mars. Find the semimajor axis of this orbit, then use Kepler's Third Law to find the period (and remember that a one-way trip requires just one-half of the period!). abacus.bates.edu /~gclough/ils/hw4.html   (512 words)

 Figure 1 At each semimajor axis, five test particles are launched at equally spaced longitudes and their initially circular orbits are integrated for 100 Myr. However, between all the terrestrial planets, there are narrow belts of stable circular orbits that survive for the full duration of integration of 100 Myr. The semimajor axes of the surviving test particles are marked by open diamonds at the top of the figure, together with symbols marking the locations of the four terrestrial planets. www.nature.com /nature/journal/v399/n6731/fig_tab/399041a0_F1.html   (268 words)

 Major Axis The longest axis of an ellipse or ellipsoid; passes through the two foci. English words defined with "major axis": Axis of a curve ♦ crosscut saw ♦ eccentricity, Ellipsoid of revolution ♦ Prolate ellipsoid ♦ rotor head, rotor shaft ♦ semimajor axis. Specialty definitions using "major axis": 2A rupture ♦ annular combustion chamber, axial ratio ♦ circumferential break ♦ elliptic reproducing stylus tip, ellipticity ratio ♦ Gantt chart, guillotine break ♦ perifocus ♦ tilting furnace. www.websters-online-dictionary.org /ma/major+axis.html   (295 words)

 Orbits   (Site not responding. Last check: 2007-10-21) The red line represents the semimajor axis and the two small sblue dots represent the two focii; the Sun is at one focus, there is nothing at the other one. We are going to use the semimajor axis and the eccentricity to calculate the perihelion and the aphelion, or how close it comes to the sun and how far it goes from the sun. As an example let's use Eros, it's semimajor axis (a) is 1.458 AU, it's eccentricity is 0.2229. www.pinecity.k12.mn.us /highschool/Astronomy/orbits.htm   (365 words)

 David Vokrouhlicky -- Papers   (Site not responding. Last check: 2007-10-21) The semimajor axes of asteroid fragments up to about 20 km in diameter drift due to the Yarkovsky effect, a subtle non--gravitational mechanism related to radiation pressure recoil on spinning and orbiting objects. Over the collisional lifetimes of these objects (typically, \$10\$~Myr to \$1\$~Gyr), orbital semimajor axes can be moved by a few times \$10^{-2}\$~AU for bodies between 1 and 10~km in mean radius. Moreover, the Yarkovsky semimajor axis mobility may spread in an observable way the tight semimajor axis clustering of small asteroids produced as a consequence of disruptive collisions. astro.troja.mff.cuni.cz /davok/papers/sci1abs.htm   (168 words)

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