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Equator An equator is the intersection of the surface of a rotating sphere (such as a planet) with the plane perpendicular to the axis of rotation and midway between its poles. On Earth, the Equator Equator is an imaginary line on the surface, equidistant from the North and South Poles, dividing the Earth Earth into Northern and Southern Hemispheres [...More...]  "Equator" on: Wikipedia Yahoo 

International Astronomical Union The International International Astronomical Union (IAU; French: Union astronomique internationale, UAI) is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy.[2] Among other activities, it acts as the internationally recognized authority for assigning designations to celestial bodies (stars, planets, asteroids, etc.) and any surface features on them.[3] The IAU is a member of the International International Council for Science (ICSU). Its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership [...More...]  "International Astronomical Union" on: Wikipedia Yahoo 

North Pole Coordinates: 90°N 0°W / 90°N 0°E / 90; 0An azimuthal projection showing the Arctic Ocean Arctic Ocean and the North Pole. The map also shows the 75th parallel north 75th parallel north and 60th parallel north. Sea ice Sea ice at the North Pole North Pole in 2006The North Pole, also known as the Geographic North Pole North Pole or Terrestrial North Pole, is (subject to the caveats explained below) defined as the point in the Northern Hemisphere Northern Hemisphere where the Earth's axis of rotation meets its surface. The North Pole North Pole is the northernmost point on the Earth, lying diametrically opposite the South Pole. It defines geodetic latitude 90° North, as well as the direction of true north [...More...]  "North Pole" on: Wikipedia Yahoo 

Year A year is the orbital period of the Earth Earth moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. The current year is 2018. A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below [...More...]  "Year" on: Wikipedia Yahoo 

Degree (angle) A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit SI unit of angular measure is the radian, but it is mentioned in the SI brochure as an accepted unit.[4] Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians.Contents1 History 2 Subdivisions 3 Alternative units 4 See also 5 Notes 6 References 7 External linksHistory[edit] See also: DecansA circle with an equilateral chord (red). One sixtieth of this arc is a degree. Six such chords complete the circle.The original motivation for choosing the degree as a unit of rotations and angles is unknown [...More...]  "Degree (angle)" on: Wikipedia Yahoo 

Sunrise Sunrise Sunrise or sun up is the instant at which the upper edge of the Sun appears over the horizon in the morning.[1] The term can also refer to the entire process of the Sun Sun crossing the horizon and its accompanying atmospheric effects.[2]Contents1 Terminology1.1 "Rise" 1.2 Beginning and end2 Measurement2.1 Angle 2.2 Time of day 2.3 Location on the horizon3 Appearance3.1 Colors 3.2 Optical illusions and other phenomena4 See also 5 References 6 External linksTerminology[edit] "Rise"[edit] Although the Sun Sun appears to "rise" from the horizon, it is actually the Earth's motion that causes the Sun Sun to appear [...More...]  "Sunrise" on: Wikipedia Yahoo 

Sunset Sunset Sunset or sundown is the daily disappearance of the Sun Sun below the horizon as a result of Earth's rotation. The Sun Sun will set exactly due west at the equator on the spring and fall equinoxes, each of which occurs only once a year.Subcategories of twilightThe time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon [...More...]  "Sunset" on: Wikipedia Yahoo 

Atmospheric Refraction Atmospheric refraction Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height.[1] This refraction is due to the velocity of light through air, decreasing (the refractive index increases) with increased density. Atmospheric refraction Atmospheric refraction near the ground produces mirages and can make distant objects appear to shimmer or ripple, elevated or lowered, stretched or shortened, with no mirage involved. The term also applies to the refraction of sound. Atmospheric refraction Atmospheric refraction is considered in measuring the position of both astronomical and terrestrial objects. Astronomical or celestial refraction causes astronomical objects to appear higher in the sky than they are in reality [...More...]  "Atmospheric Refraction" on: Wikipedia Yahoo 

Horizon The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the visible horizon [...More...]  "Horizon" on: Wikipedia Yahoo 

South Pole Coordinates: 90°S 180°E / 90°S 180°E / 90; 180The Geographic South Pole. (The flag used on the flagpole is interchangeable.)Image taken by NASA NASA showing Antarctica Antarctica and the South Pole South Pole in 2005.South Geographic Pole South Magnetic Pole South Magnetic Pole (2007) South Geomagnetic Pole South Geomagnetic Pole (2005) South Pole South Pole of InaccessibilityThe South Pole, also known as the Geographic South Pole South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface [...More...]  "South Pole" on: Wikipedia Yahoo 

Integer An integer (from the Latin Latin integer meaning "whole")[note 1] is a number that can be written without a fractional component. For example, 21, 4, 0, and −2048 are integers, while 9.75, 5 1⁄2, and √2 are not. The set of integers consists of zero (0), the positive natural numbers (1, 2, 3, …), also called whole numbers or counting numbers,[1][2] and their additive inverses (the negative integers, i.e., −1, −2, −3, …). This is often denoted by a boldface Z ("Z") or blackboard bold Z displaystyle mathbb Z ( Unicode Unicode U+2124 ℤ) standing for the German word Zahlen ([ˈtsaːlən], "numbers").[3][4] Z is a subset of the set of all rational numbers Q, in turn a subset of the real numbers R. Like the natural numbers, Z is countably infinite. The integers form the smallest group and the smallest ring containing the natural numbers [...More...]  "Integer" on: Wikipedia Yahoo 

Kourou 1 French Land Register data, which excludes lakes, ponds, glaciers > 1 km2 (0.386 sq mi or 247 acres) and river estuaries. 2 Population without double counting: residents of multiple communes (e.g., students and military personnel) only counted once. Kourou Kourou is a commune in French Guiana, an overseas region and department of France France located in South America [...More...]  "Kourou" on: Wikipedia Yahoo 

Perpendicular In elementary geometry, the property of being perpendicular (perpendicularity) is the relationship between two lines which meet at a right angle (90 degrees). The property extends to other related geometric objects. A line is said to be perpendicular to another line if the two lines intersect at a right angle.[2] Explicitly, a first line is perpendicular to a second line if (1) the two lines meet; and (2) at the point of intersection the straight angle on one side of the first line is cut by the second line into two congruent angles. Perpendicularity can be shown to be symmetric, meaning if a first line is perpendicular to a second line, then the second line is also perpendicular to the first. For this reason, we may speak of two lines as being perpendicular (to each other) without specifying an order. Perpendicularity easily extends to segments and rays [...More...]  "Perpendicular" on: Wikipedia Yahoo 

Plane (mathematics) In mathematics, a plane is a flat, twodimensional surface that extends infinitely far. A plane is the twodimensional analogue of a point (zero dimensions), a line (one dimension) and threedimensional space [...More...]  "Plane (mathematics)" on: Wikipedia Yahoo 

Reference Ellipsoid In geodesy, a reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body. Because of their relative simplicity, reference ellipsoids are used as a preferred surface on which geodetic network computations are performed and point coordinates such as latitude, longitude, and elevation are defined.Contents1 Ellipsoid Ellipsoid parameters 2 Coordinates 3 Historical Earth Earth ellipsoids 4 Ellipsoids for other planetary bodies 5 See also 6 Notes 7 References 8 External links Ellipsoid Ellipsoid parameters[edit] In 1687 Isaac Newton Isaac Newton published the Principia in which he included a proof[1][not in citation given] that a rotating selfgravitating fluid body in equilibrium takes the form of an oblate ellipsoid of revolution which he termed an oblate spheroid [...More...]  "Reference Ellipsoid" on: Wikipedia Yahoo 

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 [...More...]  "Planet" on: Wikipedia Yahoo 