1 - NGA

wortd ellipsoid used in tracking Project Mercury
manned apace misskms and as the relerence
dafum for the efecfronic navigation syslems—
Omega, ioran, and loran C. See also Fischer
ellipeold of 1960.
mercury barometer—A barometer in which
atmospheric pressure is balanced against the
weight of a column of mercury. See also
aneroid barometer; cistern barometer;
alphon barometer.
merge-To take two or more maps or data
sets and ~tne Ihem fo~elher into a single,
Coharem map or dala base wilhout redundant
Information.
merg lng—The process of joining two or more
Oveffapping data sets.
marldian altltude—The altilude of a celesliel
body when ii is on the celestial meridian ot the
obswvar.
merldlen angle difference-The dillerence
between two meridian angles, particularly
between Iha meridian angle of a celestial body
and the value used as an argument for entering
a table. Also called hour angle dlflerence.
merldlan angle-Anguler distance east or
west cd the bcal celestial meridian; the arc of
the celestial equator, or Ihe angle al the
Calestial pole, between the upper branch of Ihe
Icetl celestial meridian and the hour circle of a
C8fWflal body, measured eastward or westward
from the focal celestial meridian lhrough 180°,
and Iabelad ‘E- or “W 10 indtcale the direction
of measuramant,
merldlan d18tance-1. (astronomy) The hour
angie of a caieslial body when Ciose 10 bul not
axacrly on tha astronomic meridian. 2. (plane
surveying) The perpendicular distance in a
horizontal plane of a poinl from a meridian of
reference. The difference of the meridian
diStarSCeSOf the WTds Of a line is called the
departure of the line.
marldfan extanslon—That porfion of a
Meridian ahown above the top construction line
of a projection,
meridfan Ilna-(plane surveying) The line of
imeraacllon of the plane of the celestial meridian
and the plane of the horizon. It is a horizontal
direction usad In surveying. Ila astronomic
azimuth is O“ or 180”.
MIL-HDBK-1350
161
merldlen obaervatlon-Measurement of fhe
altitude ot a celestial body on tha celeaffal
meridian 01 Ihe obsewer, or the altitude so
measured,
merldlan paeaege—See merldlan Wanslt.
meridian teleOCope-A porfebfe Instrument
so designed fhat if can be used as an
astronomic transft, or quickly oonverfed for use
as a zenlfh faiescope.
merldlan fransfr-l%a passage of a ceieetial
body across a celestial rnaridan. Also called
marldlan paasaga. Sea also cufmlnaflon;
frenslt, definition 1.
merldlan-A north-south referanc.a line,
parficuiariy a greal circle through fhe
geographical poles ot the Earlh, horn whch
longitudes and azimuths are determined; or a
plane, normal to the gaoid or spheroid, defining
such a line. Sae aiso aatronomlc merldlan;
auxiliary guide meridian; celestial
meridian; cantral merldlan; convergence
ot marldians; doubla meridien distance;
ecllptlc merldlan; fictt!lous merldlan; .
geodetic merldlen; gaographfc
meridian; geomagnetic marldian;
Greenwich meridian; grid merldlarr;
grslde meridien; gyro merldien; IoCai
merldlan; magnetic meridian; meridional
difference; marldlonal part; meridional
plane; obliqua meridian; photograph
merldlan; prime fictitious meridian;
prime grid meridian; prima meridlen;
prime obiique merldlan; prime
tranaverae marldlan; prlnclpal meridian;
standard marldian; table of merldlonel
parts; time meridlen; transverse
meridian; true meridian.
meridional difference-The difference
belween the meridional perfa of any We gfvan
parailels. This differeme is tound by subtraction
if the two parallels are on the same aide of the
Equator, and by addition if on opposite aidea.
marldional dlsfanca-The dislance between
latitude iines as determined from the mid-
Iatilude of a map projection.
meridional intervai—Tha valua of the
dislance between meridians of a projacfion al
chart scaie.
meridional of fssfs—Smali distances appiiad