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faces, oomrnonfy expressed as me direction
dodwvtae lmm nofih.
sapherkal lens-A lens in wtich one or more
surfaces dspafl from a true sptserfcal shspa.
assault tandlng model-A 6pr3Cial 10fm of
aasauff ttwfal designed apaclfkally for planning
anmhibbus Iandiwas. Also called amohlbloua
atiault landing ‘model. See also” aasault
models.
MIL-HDBK-850
aasauft modal~arga-scale models giving a
particular representation of vagatafion, Iaaaer
Iandforrna, promlnerzt mart-made features, and a
detailed repreaenfatbn of apacftic or sansltive
ofziacfivaa such Ss alrfbkis, radar installations,
and the Mre. These models empfraslze the
aspects of objects as seen from surlaca
approach
aasoclated Legendre func.tlon-A solution
of me Lagendre equatkmr, whkh is a apeciaf
case of the Laplace equation, in the form of a
power series of a speciaf kind; used In the
spherical harmonic expansion of the gravitational
potential.
aersumed lalltud+The latitude af which an
obaewer is assumed to be located for an
observation or cxwnputaiion, as ihe latitude of an
assumed poaifion or the Iatlude used for
determining the krrrgnude by time sighf.
aeaumed longltuda-The tongitude af which
an observer is assumed to be focatad for en
obaewafkm or computation, as the longitude of
an assumed poshiofl or the brrgirude used for
determinism the fatitude by mar~!an afmude.
aSSWIMrd plaIstS coordlrratee-A iocaf plana
cormlnata eyafem aet up af the convenience of
the surveyor. The referance axes are usually
assumed so that all ceord!nates are in the first
quadrant. The y-axis may be in the direction of
asfronomk north, geodetic north, magnefic
norfh, or an assumed north.
aeaurance level—See confidence
Interval.
aatatlzeri grevlmetar-A gravlmetar,
sornalimae relemad 10 as unstable, where the
forca 01 gravfty is maintained in an unstable
equilibrium wkh lhe rastoring force. The h’ralabifiiy
is provided by the introduction of a third fome
which intensifies the atfecl of any change in
gravity fmm the value in equilibrium.
●atarold—A minor planet; one of the many
small celestial bodies revofving around the Sun,
most of tha orbits being between those of Mara
and Jupiter. Also called minor planet;
planetoid. Sea also artlflclal aalaroid.
aetlgmatlam-An aberration affectfng the
sharpness of imagas for objects off the axis in
which the rays passing through difterem
meridians of the kns come to a focus in dmaram
planes. Thus, an extra-axial polnf object Is
imaged as two mutually perpendicular attort lines
Iocalad at ditteram distances lrom the lens.
astigmatlzer—A iens which introduces
astigmafiam into an optical aysfem. Such a lens
is so arranged Ihat h can be placed in or
removed Imm the optical path at will. In a
sextam, an astipmalizer may be used 10
aSSUMOd ground alevallon—The elevation elongate fhe image of a celesfial body into a
assumed 10 prevail in the local area covared by a horizontal line.
Dartkular DhOtocrraDh or arowz of r3holeoraoh5
Used esticially-lo “denot~ the ele;ation-assumed astre flctlf—Any of several fictitious stars
to prevail in the vickrity of a crilical point, such as assumed to move abng fhe calaatial equator al
a peak or ofher (aature having abrupt bcai rafief. uniform rates corresponding to the speeds of Ihe
several harmonic mnafiruems of the tideproducing
force. Each aslre ficfif crosses the
meridian at the instant the Conslituem II
rapresenls ia at a maximum.
astro compasa-(JCS) An instmmem used
primarily to obtain true heading or true bearing by
reference to celestial bodies.
aatrodynamics—The practical applicatlrm of
celestial mechanics, aslmbaliistba, propuleiin
fheory, and allied fields to the problem of
planning and directing the frajactorfes of space
vehictes.
astrogeodetic datum orientation—The
poaMon 01 a relerance elnpsoid in relation to fhe
geoid in a speciiiad area of a geodetic nefwork. tf
may be expressed by the astmgaodalic
deflection and geoidal height at the datum point
or by an asfmgaodelic geoid charf of fhe area.
aetrogeodetlc deflection—The angfa at a
point between fhe normal to the gaoid and the
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