1 - NGA

I
tfrwerwtlcal gravity; Virtual gmvlty.
gray ecal.-see ●top wodgs.
great clrcl- cimle on the surf~e of the
Eatth, the pt911s of w4tiih ~ throu@r the
canter of fha Earih. Abe cafled orthodmm..
great ●lllptlc ●’s-h arc defined by a pfana
wllkhoontains fhatwJpdnfa and Ihacantsrof
the raferanca spheroid.
graet yem-Tfra parbd of one carrplete Wcle
of the wquinosea around the ecfi@c, about
25,S00 years. Alae called pletonk year.
grwat-clmle bamlng-The inhiif diractbn of
a great cirda through two terrestrial pdnts,
em==~ as angufw di@a* fmm a mfarence
direction. It te usually measured f- w at 1~
reference duactica clockwise to 3S0°.
grewt-olrote chart-A chart on wtriih a greet
circle appasm as a straight Iinw ❑chart on the
gnemonic prqaction.
great-clink dlrectlorr-l+orfzontel direction of
a great circle, expmssad as angular dkiance
kern e raferanca diraclion.
grwat-clrck dlctm’we-lbe length of the
efrortar arc of the great circle pining two points.
It is usualty azpraasad in nautical miias.
gmat-wlrcle line-h land eurveying, the fine
of interaadmn ef the surface of the Earth end
the plane of e graat tircle of the ceiastial
sphere.
great4rcl* routs-(JCS) The mute which
fdbwa the almrtasf arc d a great circle tefwean
two pokrts.
greatest ●longation-The maximum angular
distance cd a bdy ef the sotar syetam hem the
Sun, aB dwerved frem the Earth. The dirsdion
efthebcdy eastorwastd thati Lsuaually
~fiad, as the greatest dongation west.
Gmwrwlch ●pparant time (GA~Local
WPrent time at the Gr~nwictr nraridiin.
Qreenwlch cIvII time (GC~See
Unlvorsal Tlmo.
Grwanwlch hour ●ngle (GHA)-Angular
d~anse west of the Greenwich celestial
MIL-HDBK-850
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nwridii; the arc d the sa&ralii wyiator,or the
angfa at the oafastii equator, or the angte at
the celaatial pole, between the upper brarwh of
the Greenwich ceieatial mari.iian ●rd the hour
circle d a pebrf on the cdasfid sphere,
rnaaaurad westward from the Greenwich
oafasfid rnarirSan threugh 380°; -I hour angle
at the Greenwich meridian.
Graanwlch lntarvat-An interval baaed on
the )Aoon’s transit of the Graa~ich -ii
msridiin. as diatiiuishd frem a iccal interval
based on the Moon’s transk .4 the local c9taet!!l
rnatidisn.
Graanwlch lunar tkna-Local lunar time at
lha Greenwich rnaridiim the arc of the Aasfii
equator er the angle, at tha cafaatial pole,
between the lower branch of the Gmanwrs+
Cataatial mwkfian and ths hour circle of the
Moon, measured wesfwatd fmrn the kwer
branch of tha Grwwhvich oakr.sti.slmeridian
through 24 hours: Graamvkh hour angia of the
Mom, expressed in time unka, p4ua 12 hours.
Graanwich Mean Time (GMT)-(JCS) Also
called Greenwich civil tlma; z-time: Zulu
timm See ltnlveraal Tlma.
Greenwtch meridian-The meridian through
Greanti, England, ewving as the raferanca
for Greenwich time, in centrast with tit
merkfkrns. It is accepted almos4 untiersaliy as
the prims meridian, or the origin d
measurement of tongituda.
Gmenwlch ●ldereaf data-Tha number of
mean sidereai days thal have ekpaed a the
Greenwich meridian since the beginning of the
sidereal day that was in pmgraas at Greenwich
maan neon on January 1, 4713 B.C. see also
Gmanwich aldoreal day number.
Gmonwich ●lderoal day number—The
integral pert of the Greenwich sidereal date. It is
e mearm d nurrbrirrg umsacuttidy ●uxaaaive
akfereal daya beginning at the instrmts d qpr
transit of the mean vernal equinox over the
Greenwich nreridiin. See atao Groonwlch
oldamal date.
Gmwrwich sidamef tlmo (GST)-Local
sidereal time at the Greenw~h meridian. Tfw am
sf the celestial aquamr, or ths angie al the
#astial pole, between the tqpar bmndt d the
3raenwich cafeatial rneridiin end the hour side
>f the varnal equinox, measured westward from
ha upper trranch of the Greenwich cabstial