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magnetic enomaly.
MIL-HDBK-850
Wmrrtely-1. (general) A deviafhn fmm the
norm. 2. (geodesy) A davialion of an obserwed
vahse horn a lheoretkrrf value due to a
correaptmdrrg irregularity in the Earth’s structure
at Ike area of obaervafkm. 3. (astronomy) The
angle bafwaen the radhss vector to an orbithg
Ix@ fmm ifs primary and the line of apairfss of
Iha orbii, rneawmd in Iha duacfion of travel. horn
the point of cbaaaf a~ruach to the primary. This
term ia also called the true ●nornely when if is
desired to diafingulsh If from the eccentric
atWtMaly, which is the correapmdhrg angle at
tha cenfar of the orWf: or from the mean
anomaly, which is what the true artOMSly would
bacems ff the pfanat had a uniformly argufar
motbn. 6s8 also Bossguer ●nomaly;
deflection ●nomaly; free-air ●romely;
gravity smomaly; Hayford gravity
anomalles; height enomaly; Iaoetatlc
anomaly; local magnetic anomaly;
magnetic dlaturbance; mean trae-elr
enomaly; point anomaly; aurlace
anomeliea.
Anlarctlc Circle-The gaogrephlc parallel
heving a south Ia!itude equat to the complement
01 the declination 01 the wimer aoksfiie. The
obl~uhy et the acffpfk Ls$teadlly changing so
that Iha wimar solstice la not a poinl of fiiad
decfinstbn, and the Anfarctk Circla, as defined,
is net a Iirm of Siied position. When the Antarctic
Ctrcle is to be shown on a map, however, If k
desirable that If be traatad as a Ilna of fixed
position, and that a conventional valua be
adopted for its latitude. For thie purpose, tha
vslue 66°33’ south fatifucfe Is used. Alao calied
south polar circle.
antlhalatlorr coatfng-(photography) A fi9hh
abaorblng Coating applied 10 Ihe backside of the
auPPOr’fOf a film or plate (or between the
emulsion and tha suPPort) to suppress halation.
antlporSa-AnythinQ exactly Oppcrtilte to
aomefhing alse. Parfioutarfy, thaf point on the
Earth 180” horn a gfven place.
arrtlaolar point-That point on the calastial
sphere 180” fium the Sun.
antfvfgnafftng filter—(JCS) A flffar traarlrrg a
deposil which Is graduated In density to correct
for the uneven Itlumlnafion given by cerfafn
Ianses, Parllwlerly wide-ar@e fypas.
apareon—The polnf on a Mars-centered orbit
where a satellite is at ffs graatesl distance fmm
Mars.
●paetron—Tfsat Polnf ot Ihe orbti of one
marr_bar of a double star system at whkh the
stars are farthest apart. Opposite of perlaatron.
aperlodlc compaa-fferally “a compass
without a period,- or a compass that, after being
deflected, returns by one dhacf movement to Ifs
pmpar raading, without oscillafiin. Afso called
deadbeat compeae.
●periure ratio—See relatlve ●perture,
aperture afop-(optks) The phyaicaf alernanf
(such as a afop, diaphragm, or fans pa~hery) of
an optkal system whkh limits the size of the
pencil of rays traversing tha system. The
adjustment of the size of fhe aperture stop of a
@ven system regulates the brightness of fhe
Image without nacassarily affecting the size of
the area oovared. Aleo called etop.
aperture-l. The opening In a lens diaphragm
through which light pasaes. 2. The diamefer of
the objecfive lens O! a Ialeaoopa or of her optical
instrument, usually exfxasaad in irwhas, buf
sometimes as the anffla between lines from fhe
principal focus to opfmsffe ends of a diameter of
the objeclive lens. See also relallve aperfura,
apex—See vertex.
aphaflon—The point in fhe alllpffcal orbff of a
planet which is the farthest fmm the Sun, when
lha Sun is the cenler of affracfbn. Opposffe of
perlheflon.
aphylactlc mep projection-A map
projecfiin which ekes not possess any of the
three special pmparlies of equivalence,
conforrnafiiy, or erfuidisfarrca. Afao called
arbitrary pro]ectlon.
eplanatk lens-A lens which transmits fiiht
without spharical ahrrafion,
aplune (apoluna)—The point on the elliptical
Mbif of a aalellffe of the Moon which is farlhes!
Irom the Moon. Alao called epocynthlon.
( Opposite of perflune; perlcynthlon.
1mpoapala-See
apocenter.
!pocenter-in an alfiptical orbii. the poinl in the
xbif whfch is the graalest distance from the
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