1 - NGA

Ioxodromlc curve-See rtrumb line.
lunar celestiel equator—A great circle on
the celestiaf sphere in the plane of the
Moon’s equator, i.e., in a plane
perpendicular to the Moon’s axis of
rotat ton.
lunar chart-A charl showing the surlace 01
the Moon.
lunar cycla-Any cycle related 10 the Moon,
particularly the Callippic cycle or Ihe
MeIonic cycle. See also saros.
lunar day—The interval between two
successive upper transits of Ihe Moon over
a local meridian. The period of Ihe mean
lunar day, approximately 24.S4 solar hours,
Is derived from the rotation of the Earth on
its SXiS relative to the movement of the
Moon aboul the Earth. Also called tldaf
day.
lunar declination—Angular distance 01 the
Mcen expressed in degrees north or south
of the ceieslial equator; it is indicated as
posllive wnen norm. and negative when
south of lhe equa!or. Also called
declination of the Moon.
lunar dla!ance—The angle between the line
of sight toward Ihe Moon and the line o!
sight toward another celestial bedy at Ihe
point 01 an observer on lhe Earth.
lunar aartfselde than—A chart showing
that portion of lha Moon% surtace visible
from” the Earlh,
lunar ecllpae-The phenomenon observed
when the Moon enlers Ihe shadow of the
Earth. A lunar eclipse is partial if only part ot
ifs surface is obscured; and tolal if the
entire surface is obscured.
lunar equation—A Iaclor used m reduce
observatbms of celestial bodies to the
barycenter of the Earlh-Moon system.
lunar faralde chart-A chart showing that
portion of the Moon’s surface rwt visible
from the Earth.
Iuner Inequellt y—1. Variation in the
Moon’s motion in its orbit, due to attraction
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149
by other bodies of the solar system. Sae
also evectlon; parlurbatlon. 2. A
rninu!e fluctuation ot a magnetic needle
horn fts maan pcsltiin, caused by Ihe
Moon.
lunar Interval-The dltferance in lime
behveen the transit of tha Moon over the
Greenwich meridian and a local meridian.
The lunar interval equals the diflemnce
between the Greenwich and total intenfala
of a tide or current phase.
lunar month—See aynodlcal month.
Iuna r nods-A node of the Moon’s orbii.
tunar parallax—The horizontal parallax or
the geocentric parallax of the Moon.
lunar aatelllte-A man-made safellite that
makes one or more revolutions about the
Moon.
Iuner tida-Thai part ot the tide caused
solely by the tide-producing forces of the
Moon as distinguished trom that parl
caused by the tortes Of the Sun.
lunar Urns-l. Time based upon the
rotation of Ihe Earth relative to the Moon.
2. Time on the Moon. See also
Greenwich lunar time; local lunar
time.
lunatlon—See aynodlcal month.
I u ne—Thai part ot the sutlace of a sphere
bounded by halves of two great circles.
lunlcentrlc—See ealenocentric.
.Iu nlaolar effect—Gravitational elf acls
caused by lhe a!lraction of fhe Moon and
of the Sun.
Iunlsolar perturbation-Perfurbafions of
artificial satellite orbits due to the attractions
of the Sun and the Moon. Tha mosf
Imporlanl effects are secular variations in
me mean anomaly, in the right ascension
01 the ascanding node, and in the
argument of perigee. All other orbital
elements, except the mapr semiaxis,
undergo long periodic changes.
Iunlsolar preceaalon—lhat component ‘of