1 - NGA

nodal point of lncldence—Sae
point, definition 1.
nodal
nodal point-l. (optics) One 01 Iwo points
on the optical axis 01 a lens, or sysiem 01
lenses, such Ihal a ray emergent from the
sacord pmint is parallel to the ray incidenl
at tha first, Ttris first nodal point is also
referred to as the front nodal point,
Incident model point, or nodal polnl
01 Inclcfenca; and !he second poinl as
the rear nodal polrtt, emergent nodal
point, or nodal polnl 01 amarganca.
Also celled nods. 2. (astronomy) See
node, definition 1. 3. (hydrography) See
amphldromlc point.
noda cycle-The lime required (or the
regression of the Moon’s nodes 10
complete a circuil of 360= of longitude: a
period of approximately 16,6 years.
node-1. (astronomy) One of the two poinls
of intersection o! the ortil of a planet,
planetoid, or comet with the ecliptic, or of
the orbit 01 a satellile wilh the equatorial
plane 01 the orbh 01 its primary. Also called
nodal point. See also ascending
node; dascendlng nods; ecliptic
node; equatorial node; line of
nodes; Iongltude of the Moon’s
nodes; lunar node; regression 01
tha nodes. 2. (oplics) See nodal
polnl, definition 1. 3. A unique poinl
representing the Iocalion ot a teature, 01
the location of an intersection or connection
of some number o! tea!ures. Alternatively,
a node is any isolated point, or the junction
of any two or more edges, or the erid
points of an edge.
nodlcal morr!h-The interval of lime
banvean two successive passages ot Ihe
Moon through the same noda of its orbit,
aPPrOximalelY 27 days, Also called
dracontc month.
nodlcal period—The interval between two
successive passages 01 a salelfile or planel
through the ascending node of its orbit.
nolaa lavel—The magnitude of random
errors in a particular type 01 measurement,
nominal focal length—(JCS) An
approximate ValUe Of the focal length,
rounded off to some standard figure, used
MIL-HDBK-850
171
ior the classification of lenses, mirrors, or
cameras.
nominal orbli—Tha true or ideal orbit upon
which a space vehicle is expected to msval.
nomogram—A diagram showing, to acafe,
the relationship between several variables
in such manner that tha value of ona which
corresponds to known vefues ot the others
can be determined graphically.
Non-Submarine Contact (NSC) Llate—
Lists which contain a tabulated fist of
wrecks and other obstructions which might
be construed as submarine by sonar.
nonautomatic rectlflar-Any rectifiar which
requiras compulalbn of the elemenls of
rectification, each of which must be
manually set on its corresponding circle or
scale on the rectifier.
nongrevilationsl parturbatione—
Perturbations caused by surface forces due
to mechanical drag of the atmosphere (in
case 01 low flying satellites),
eiecvOmaQnelism, and radialion pressure.
nonmonumented bench mark—See
temporary bencn mark.
nonperspectlve azimuthal map
projection—A projection not based on
perspective lines of sigh! from a single poim
of view.
nonselective filtar—A lilter Ior which
transmittance is sutrslamially independent
of wavelength.
nontiltlng-fens rectltler—A clesa of retillier
wherein the lens is constrained to rnova in
the direction o! its fixed esis.
nontfltlng-negative-pfane rectlfler— A
ClaSS ot rectifier which Conlalns a nomiltfng
negative carriar. In this class of racfffiars,
the negaliva carrier plane remains
horizomal.
normal dlstrfbutlon !unctlon—A
mafhemaficaf funclion describing the
behavior of one-dimensional random errors.
normal equation—One of a set of
simultaneous equafions derived from