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at the economical speed and altitude at all stages of the flight.
Revolution (of the earth)—The earth's elliptical path about the sun which determines the length of the
year and causes the seasons.
Rhumb Line—A line on the surface of a sphere that makes equal oblique angles with all meridians. A
loxodromic curve.
Running Fix—A fix determined from a series of lines of position, based on the same object or body and
resolved for a common time.
Scan—The motion of an electronic beam through space searching for a target. Scanning is produced by
the motion of the antenna or by lobe switching.
Semidiameter (SD)—The value in minutes of arc of the radius of the sun or the moon.
Sextant—An optical instrument normally containing a two-power telescope with a 15° field of vision. It
also contains a series of prisms geared to an altitude scale permitting altitude measurement of a celestial
body's altitude from -10° below the horizon to 92° above the horizon.
Slant Range—The line of sight distance between two points, not at the same level relative to a specific
datum.
Solstice—Those points on the ecliptic where the sun reaches its greatest northern or southern
declination. Also the times when these phenomena occur.
Summer—That point on the ecliptic where the sun reaches its greatest declination having the same
name as the latitude.
Winter—That point on the ecliptic where the sun reaches its greatest declination having the
opposite name as the latitude.
Speed Line—A line of position that intersects the track at an angle great enough to be used as an aid in
determining groundspeed.
Spot-Size Error—A distortion of a radar return caused by the size of the electron spot in a cathode-ray
tube.
Standard Lapse Rate—A temperature decrease of approximately 2° centigrade for each 1,000 feet
increase in altitude.
388 AFPAM11-216 1 MARCH 2001
Star Magnitude—A measure of the relative apparent brightness of stars.
Statute Mile—5,280 feet or .867 nautical miles.
Subpoint—That point on the earth's surface directly beneath an object or celestial body.
Sun Line—A line of position obtained by computation based on observation of the altitude of the sun
for a specific time.
Sweep—The luminous line produced on the screen of a cathode-ray tube by deflection of the electron
beam. Also called time base line.
Sweep Delay—The electronic delay of the start of the sweep used to select a particular segment of the
total range.
Target-Timing Wind—A wind determined from a series of ranges and bearings on the same target
taken within a relatively short period of time.
Time:
Apparent Time—Time measured with reference to the true sun. The interval which has elapsed
since the last lower transit of a given meridian by the true sun.
Greenwich Mean Time (GMT)—Local time at the Greenwich meridian measured by reference to
the mean sun. It is the angle measured at the pole or along the equator (and converted from time)
from the lower branch of Greenwich meridian westward through 360° to the upper branch of the
hour circle through the mean sun.
Greenwich Sidereal Time (GST)—Local sidereal time at Greenwich. It is equivalent to the
Greenwich hour angle of Aries converted to time.
Local Mean Time (LMT)—The time interval elapsed since the mean suns transit of the observer's
antimeridian.
Local Sidereal Time (LST)—Local time at the observer's meridian measured by reference to the
first point of Aries. It is equivalent to the local hour angle of Aries converted to time.
Mean Time—Time measured by reference to the mean sun.
Sidereal Time—Time measured by reference to the upper branch of the first point of Aries.
Standard Time—An arbitrary time, usually fixed by the local mean time of the central meridian of
the time zone.
Zone Time—The time used through a 15° band of longitude. The time is based on the local mean
time for the center meridian of the zone.
AFPAM11-216 1 MARCH 2001 389
Z or Zulu Time. (NATO)—Greenwich mean time. (DOD: Coordinated Universal Time.) Expressed
in four digits
Time Zone—A band on the earth approximately 15° of longitude wide, the central meridian of each
zone generally being 15° or a multiple removed from the Greenwich meridian so that the standard time
of successive zones differs by 1 hour.
Track (Tr)—The actual path of an aircraft above the surface of the earth.
Twilight—The periods of incomplete darkness following sunset and preceding sunrise. Twilight is
designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is
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