lnuenting the Globe Lines of l,ongitude and latitude

lnuenting
theGlobe
ArcticCircle
\bu can tell by photographstaken from spacethat the earth is round. But, if
r ou look out a window at school or home, the surfaceof the earth
lppean mainly flat.
Yet more than 2,000 years before photography from
spacewas possible,the ancient Greek geographers
relied on observationand mathematicsto figure out
the shapeand size of the earth. They made the first
globes to show what the earth is like.
Lines
of l,ongitude
andlatitude
The ancientGreeksalso usedtheir globesto think
aboutthe location of placeson the earth.They divided
the _elobeinto 360 segments,calleddegrees.They used
rertical lines called longitude to mark off the 360 parts.
Lines of longitude,also calledmeridians, are still used
today to locateplaceson the earth,and to measure
the distancesbetweenplaces.They can be seenon
most globes.
T\e pime meri.dinn,or 0 degrees(0') longitude,was
a_ereed
upon in 1884.It passesthrough the site of the
Royal Naval Observatoryin Greenwich,England.Distance
is measuredeastand west of this line. Longitude lines
I/
--.r
f tL- ^-i-^
^-:,{:^^-^ -,,*L^-^l
L-^---t^
east^of
the prime -meridian
are
numbered11'" athrough
179".This is the easternhemisphere.Longitude
Iineswest of the prime meridian are also
w
numbered1'through 179'. This is the western
hemisphere.The 180"line, reachedby travelingeastor
s'est from the prime meridian, is exactly halfway around
the earthfrom the prime meridian.Much of this line of
longitudeis used also as the international date line (seep. l5).
The ancient Greeks also drew lines to divide the earth horizontally. These
lines are called lines of latitude or parallels. Latitude is measuredfrom the
equator, or 0 degrees(0') latitude. Latitude lines are numberedfrom 0" to
90" from the equator to the north pole. The part of the earth from the equaror to the north pole is called the northern hemisphere. Latitude lines are
also numbered0" to 90" from the equatorto the southpole. The part of the
earth from the equator to the south pole is called the southern hemisphere.
The northern hemisphereis divided into the tropics and temperate zone at
the Tropic of cancer, a line of latitude that runs parallel to the equator at
23"30'north latitude.The temperatezone runs from 23"30'to the Arctic
circle, a line of latitude locatedat 6630'north latitude.In the southern
hemisphere,the Tropic of capricorn, locatedat23"30'south latitude,
dividesthe tropics from the southerntemperatezone.The temperatezone
endsat the Antarctic Circle, or 66'30' southlatitude.
Lines of latitude run parallel to each other; that meansthey never meet.
Antarctic
Circle
linesof longitude
The Two North Poles
IO"
Tropicof
Cancer
The spot where the lines of longitudemeet at the
northernmostpoint of the globe is called the north
pole. It is also called true north, or geographir
north.
There is another north pole; called magnetic
north. The magnetic north pole is not located in
quite the sameplace as the geographicalnorth pole,
although they are very close. The difference
betweenthe location of the true north and magnetic
north poles is shownon most globes.
You can find the magnetic north pole with a
compass.A compassis madeof a magnetized
needle held up so that it turns freely. Becausethe
earth itself is a huge magnet, no matter what
direction you're going, the compassneedle
alwayspoints to magneticnorth.
equator
of latitude
'il-xic of capricorn
Degrees of longitude and latitude are
divided into measurescalled minutes,
'.
and markcd by the symbol Like minutes in an hour, there are 60 minutes
(60') in a degree of longitude or latitude. Minutes are divi"dedinto seconds,
and marked by the symbol". There are
60 secondsin each minute of lntitude
or longitude.
11
c:::r' t:eorraphers
establishecl
the :cience .i nrakin-e
highil, accurateglobes.The globes
. . 1 . 3t ' i t h e n t o : t i n t p o r t a n t
are basedon
discoreries
ntade br earlv Greek o.^or.qhharo
Eratostttert,,
oj'cri',',;i;t"'jjffi;]::;::r'il,1r"Jili,:TilT,::!:
orround
objecrs
(spheres),
to
toth-e
measuremenr
used
,,.',:lffil'l:5?i',iT:Tili;i';il'l.ll;;,:.;";;;;;;',-,^,.ro,.
byscienHipparchus(born c' 150e'c') refined
measurements
for latitudeand deveroped
measures
longitude(seep' I0)' He was the firstto
for
divide trr. equato.into360 de-erees.
Fiipparchus
alsodivided
ihe * orid as he knew it into climaticzones(see
p. soj ano ar.w the f,J i;;;;
map of the night sky.
strabo (60 e'c'-a'o' 25) describedhis travels
itr-ugtr Er.op., North Africa, and western
calledGeographia'written as l7 books,Geograpnio'i"rriiaes
Asia in a work
in detailtrrerno.roas rhe Greeksof
tinteknew it.
his
claudiusPtolemy
centurya.o.) wrotgan eight-volume
book,
described
rn it,he
in termsor^(2nd
iongituo"ui,oiuii ude(seep Tol uil-irr"pracesalsocalled,Geographia.
in rheworldrhatwereknownro rhe
Greeks
of thistime.
TheGeographic
Grid
Linesof latitudeand.longitude.
form a geographicgrid.
Thegeo-qraphic
grid.makes
it possibTe
to ia.ntiri poinr,on theearthand
recordtheirexactrocarions
northor southof rh. .d;i;; Jnoeastor u.esr
of
theprimemeridian.
NorthPole
NorthPole
/i
i'/ I I
---l* *f---t-'+--+
''/',l,ii
90"s
SouthPole
90"s
SouthPole
usingcoordinates'-or
pointsof
latitudeand rongitude,
yo-ucanrocatethe praces
sur-race'
includins
on the earth,s
Anchorase'
niJir<Jior:north
lZiii.lj.,'rso"*9s!ioirlilli;r,
n4 nortnlatitude'
Banskok,
rhairancl
roo."east
tongiiudel
e"rb;v, r"iJ,lii\g"
nqrq.r
(2T"south
Austratia
larilt;;;,.easronsituder,
tatitude,
erisbane,
rss'eillloro,tyq;,i,,a;jri,
i.ovpleo,iliti t,rtitror,sr.eastron,gituoer,
capetown,
southAfrica
rsq.'south
6tituo6,le-.i;i"ioin,l,rgqlr.poelnasen,
(s6"n6rtn
Denmark,
gg'Wedt
,,,,,u0.-,
8,lilJ?fj
ronsitude),
1r;f,X'lj.]i.?j,.lg:t,#..#.S;?[rirkl.;iibi;;?l,n
ano
iantiaso,