instance_of international latitude observatory
The Equator usually refers to an imaginary ___MASK60___ on the Earth ' s ___MASK97___ equidistant from the North ___MASK3___ and South ___MASK3___ , dividing the Earth into the Northern Hemisphere and Southern Hemisphere . The Equator is about long ; some 78 . 7 % lies across water and 21 . 3 % over land . A ___MASK15___ ( from Greek   " sphaira ", " globe , ball ") is a perfectly round geometrical object in ___MASK84___ - dimensional space that is the ___MASK97___ of a completely round ball , ( viz ., analogous to a circular object in two dimensions ). Earth , otherwise known as the world , is the third ___MASK26___ from the Sun and the only object in the Universe known to ___MASK58___ life . It is the densest ___MASK26___ in the Solar ___MASK14___ and the largest of the four terrestrial planets . North is a noun , ___MASK93___ , or adverb indicating direction or ___MASK9___ . North is one of the four cardinal directions or compass points . It is the opposite of south and is perpendicular to east and west . In ___MASK9___ , latitude is a geographic coordinate that specifies the north  south position of a point on the Earth ' s ___MASK97___ . Latitude is an angle ( defined below ) which ranges from 0 ° at the Equator to 90 ° ( North or South ) at the poles . Lines of constant latitude , or parallels , run east  west as circles parallel to the equator . Latitude is used together with longitude to specify the precise location of features on the ___MASK97___ of the Earth . Approximations employed . Two levels of abstraction are employed in the definition of these coordinates . In the first step the physical ___MASK97___ is modelled by the geoid , a ___MASK97___ which approximates the mean ___MASK7___ level over the oceans and its continuation under the land masses . The second step is to approximate the geoid by a mathematically simpler reference ___MASK97___ . The simplest choice for the reference ___MASK97___ is a sphere , but the geoid is more accurately modelled by an ellipsoid . The definitions of latitude and longitude on such reference surfaces are detailed in the following sections . Lines of constant latitude and longitude together constitute a graticule on the reference ___MASK97___ . The latitude of a point on the " actual " ___MASK97___ is that of the corresponding point on the reference ___MASK97___ , the correspondence being along the normal to the reference ___MASK97___ which passes through the point on the physical ___MASK97___ . Latitude and longitude together with some specification of height constitute a ___MASK42___ as defined in the specification of the ISO 19111 standard . The geoid is the ___MASK47___ that the ___MASK97___ of the oceans would take under the influence of Earth ' s gravity and rotation alone , in the absence of other influences such as winds and tides . This ___MASK97___ is extended through the continents ( such as with very narrow hypothetical canals ). All points on the geoid have the same gravity potential energy ( the sum of gravitational potential energy and centrifugal potential energy ). The force of gravity acts everywhere perpendicular to the geoid , meaning that plumb lines point perpendicular and ___MASK29___ levels parallel to the geoid . ___MASK9___ ( from Greek , " geographia ", literally " earth description ") is a ___MASK87___ of science devoted to the study of the lands , the features , the inhabitants , and the phenomena of Earth . The first person to use the word "  " was Eratosthenes ( 276  194 BC ). ___MASK9___ is an all - encompassing discipline that seeks an understanding of the Earth and its human and natural complexities  not merely where objects are , but how they have changed and come to be . It is often defined in terms of the two branches of human geography and physical geography . The four historical traditions in ___MASK48___ research are : spatial analyses of natural and the human phenomena , area studies of places and regions , studies of human - land relationships , and the Earth sciences . ___MASK9___ has been called " the world discipline " and " the ___MASK57___ between the human and the physical sciences ". South is a noun , ___MASK93___ , or adverb indicating direction or ___MASK9___ . It is one of the four cardinal directions or compass points . South is the polar opposite of north and is perpendicular to east and west . A ___MASK85___ , telluric planet , or rocky planet is a planet that is composed primarily of silicate rocks or metals . Within the Solar System , the terrestrial planets are the inner planets closest to the Sun , i . e . Mercury , Venus , Earth , and Mars . The terms " ___MASK85___ " and " telluric planet " are derived from Latin words for Earth (" Terra " and " Tellus "), as these planets are , in terms of ___MASK35___ , " Earth - like ". A ___MASK42___ is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers , letters or symbols . The coordinates are often chosen such that one of the numbers represents a vertical position , and two or three of the numbers represent a horizontal position . A common choice of coordinates is latitude , longitude and elevation . An ellipsoid is a closed quadric ___MASK97___ that is a three - dimensional analogue of an ellipse . The standard equation of an ellipsoid centered at the origin of a Cartesian coordinate system and aligned with the axes is Longitude ( or , Australian and British also ), is a geographic coordinate that specifies the east - west ___MASK56___ of a ___MASK52___ on the Earth ' s ___MASK97___ . It is an angular measurement , usually expressed in degrees and denoted by the Greek ___MASK90___ lambda (  ). Meridians ( lines running from the North Pole to the South Pole ) connect points with the same longitude . By convention , one of these , the Prime Meridian , which passes through the Royal ___MASK2___ , Greenwich , England , was allocated the ___MASK56___ of zero degrees longitude . The longitude of other places is measured as the angle east or west from the Prime Meridian , ranging from 0 ° at the Prime Meridian to + 180 ° eastward and  180 ° westward . Specifically , it is the angle between a plane containing the Prime Meridian and a plane containing the North Pole , South Pole and the location in question . ( This forms a right - handed coordinate system with the axis ( right hand thumb ) pointing from the Earth ' s center toward the North Pole and the axis ( right hand index finger ) extending from Earth ' s center through the equator at the Prime Meridian .) The Sun is the ___MASK99___ at the center of the Solar ___MASK14___ . It is a nearly perfect sphere of hot plasma , with internal convective ___MASK55___ that generates a magnetic field via a dynamo process .< ref name =" doi10 . 1146 / annurev - astro - 081913 - 040012 "></ ref > It is by far the most important source of energy for life on Earth . Its diameter is about 109 times that of Earth , and its mass is about 330 , 000 times that of Earth , accounting for about 99 . 86 % of the total mass of the Solar ___MASK14___ . About three quarters of the Sun ' s mass consists of hydrogen (~ 73 %); the rest is mostly helium (~ 25 %), with much smaller quantities of heavier elements , including oxygen , carbon , neon , and iron . Life is a characteristic distinguishing physical entities having biological processes , such as signaling and self - sustaining processes , from those that do not , either because such functions have ceased , or because they never had such functions and are classified as inanimate . Various forms of life exist , such as plants , animals , fungi , protists , archaea , and ___MASK41___ . The criteria can at times be ambiguous and ___MASK98___ or ___MASK98___ not define viruses , viroids , or potential artificial life as " living ". Biology is the primary ___MASK78___ concerned with the study of life , although many other sciences are involved . The Universe is all of ___MASK70___ and space and its contents . It includes planets , moons , minor planets , stars , galaxies , the contents of intergalactic space , and all matter and energy . The size of the entire Universe is unknown . The International Latitude Observatories were a ___MASK14___ of ( originally ) six observatories located near the parallel of 39 ° 08 ' north latitude . They were used to measure the variation in latitude that occurs as a result of the `` wobble '' of the Earth on its polar axis . The original six observatories were located in : Gaithersburg , Maryland Cincinnati , Ohio Ukiah , California Mizusawa , Iwate , Japan Charjui , Turkestan Carloforte , Italy The Solar ___MASK14___ is the gravitationally bound ___MASK14___ comprising the Sun and the objects that orbit it , either directly or indirectly . Of those objects that orbit the Sun directly , the largest ___MASK37___ are the planets , with the remainder being significantly smaller objects , such as dwarf planets and small Solar ___MASK14___ bodies . Of the objects that orbit the Sun indirectly , the moons , two are larger than the smallest planet , Mercury .