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#LENCONG [[Bulatan agung]]
{{for|pertubuhan antara bintang fiksyen bernama ''Great Circle''|Andromeda (novel)}}
[[Fail:Sphere halve.png|thumb|right|Sebuah bulatan besar membahagikan sfera dalam dua [[sfera|hemisfera]] sama]]
'''Bulatan besar''' sebuah [[sfera]] adalah sebuah bulatan yang berlari di sepanjang permukaan sfera itu supaya dapat memotongnya kepada dua setengah yang sama, berbeza dari [[bulatan kecil]]. Iaitu, ia adalah persilangan sebuah sfera dan suatu [[satah asasi|satah]] yang melintasi titik pusat sfera itu. Kesemua bulatan besar suatu sfera mempunyai [[lilitan]] dan [[pusat (geometri)|pusat]] yang sama. Sebuah bulatan besar adalah bulatan terbesar yang dapat dilukis pada mana-mana sfera yang diberikan. Setiap bulatan adalah bulatan besar tepatnya satu sfera.
Bulatan besar berkhidmat sebagai analogi "garis lurus" dalam [[geometri sfera]]. Lihat juga [[trigonometri sferia]] dan [[geodesik]].
Bulatan besar, juga digelar [[bulatan Riemannian]], adalah laluan dengan [[kelengkungan]] terkecil, dan oleh itu, sebuah lengkok (atau sebuah '''ortodrom''') sebuah bulatan besar adalah laluan terpendek di antara dua titik di permukaan. Jarak di antara mana-mana dua titik pada sebuah sfera oleh itu digelarkan [[jarak bulatan agung]].
== Geodesik Bumi ==
:Lihat juga [[Geodesi]]
[[Fail:OblateSpheroid.PNG|250px|right|thumb|[[Sferoid buntal]]]]
Mengatakan secara had [[reference ellipsoid|bukan sebuah sfera sempurna]] Bumi (ia sebuah sferoid buntal atau ellipsoid – i.e., slightly squashed at the poles), yang bermakna bahawa jarak terpendek di antara dua titik (sebuah geodesic) adalah agak bukan sebuah lingkaran besar. Sunggpuhpun, model sfera dapat dianggap suatu penganggaran pertama.
Apabila penerbangan jarak panjang atau jalan nautika dilukis pada sebuah peta datar (misal kata, [[anggaran Mercator]]), mereka sering lihat berlengkung. Ini adalah kerana mereka terletak pada lingkaran-lingkaran besar. Suatu jalan yang akan melihat seperti garis lurus akan sebenarnya lebih panjang. Suatu pengecualian adalah [[anggaran gnomonic]], dalam mana semua garis lurus mewakili lingkaran besar.
On the Earth, the [[Meridian (geography)|meridians]] (or ''lines of longitude'') are on great circles, and the [[equator]] is a great circle. Lines of [[latitude]] are not great circles, because they are smaller than the equator; their centers are not at the center of the Earth -- they are [[small circle]]s instead. Great circles on Earth are roughly 40,000 km in length, though the Earth is not a perfect sphere; for instance, the equator is 40,075 km.
Some examples of great circles on the [[celestial sphere]] include the [[celestial horizon]], the [[celestial equator]], and the [[ecliptic]].
[[File:Greatcircle Jetstream routes.svg|left|thumb|400px|Airline routes between [[San Francisco]] and [[Tokyo]] following the most direct great circle (top), but following the jet stream (bottom) when heading eastwards]]
Great circle routes are used by ships and aircraft where currents and winds are not a significant factor. [[Flight length]]s can therefore often be approximated to the [[great-circle distance]] between two airports. For aircraft travelling west between continents in the northern hemisphere these paths will extend northward near or into the [[Arctic]] region, however easterly flights will often fly a more southerly track to take advantage of the [[jet stream]].
If one were to travel along a great circle, it would be difficult to steer manually as the heading would constantly be changing (except in the case of due north, south, or along the equator). Thus, Great Circle routes are often broken into a series of shorter [[rhumb line]]s which allow the use of constant headings between [[waypoint]]s along the Great Circle.
{{BI|Great circle}}
==Lihat juga==
* [[Geodesic]]
* [[Rhumb line]]
* [[Small circle]]
* [[Kiblat]]
==Pautan luar==
* [http://mathworld.wolfram.com/GreatCircle.html Great Circle – from MathWorld] Great Circle description, figures, and equations. Mathworld, Wolfram Research, Inc. c1999
* [http://www.gcmap.com/ Great Circle Mapper] Interactive tool for plotting great circle routes.
* [http://v-flyer.com/the-toolbox/blue-marble-mapper Blue Marble Mapper] Draws Great Circle routes between airports using the NASA Blue Marble as the base map.
* [http://www.aircalculator.com Air Route Calculator and Maps] See Great Circle routes between most airports using Google Maps. See closest and furthest airports from origin and destination.
* [http://williams.best.vwh.net/gccalc.htm Great Circle Calculator] deriving (initial) course and distance between two points.
* [http://www.acscdg.com/ Great Circle Distance] Graphical tool for drawing great circles over maps. Also shows distance and azimuth in a table.
* [http://demonstrations.wolfram.com/GreatCirclesOnMercatorsChart/ Great Circles on Mercator's Chart] by John Snyder with additional contributions by Jeff Bryant, Pratik Desai, and Carl Woll, [[Wolfram Demonstrations Project]].
[[Kategori:Geometri permulaan]]
[[Kategori:Trigonometri sfera]]
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