Nautical Know How - Glossary of Nautical Terms
Circle surrounding a centred dot - Right Ascension of the Meridian; (+) Circle . the lubber line (a vertical black line on the compass bowl) vertical and in the keel line of the ship. . They point at an angle either East or West of the North and South. .. parallel to one, and will intersect the point from which you intend to depart. In a line approximately at right angle to the ship's keel opposite the waist or middle part The convergence to different foci, by a lens or mirror, of parallel rays of light. .. The altitude of a celestial body on the celestial meridian is called meridian altitude. Point on a tidal chart where the cotidal lines meet. A basic geography questions - Do all of the parallels and the meridians cross each other at right angles on both the globe and Mercator? which main parallels .
A unit of area equal to 43, square feet. An artificial satellite which transmits an electromagnetic signal. As defined by International Telecommunications Union ITUan earth satellite carrying a station intended to transmit or re transmit radio communication signals. A satellite tracking system which operates by transmission of signals to and receipt of responses from the satellite. Motion of an object relative to the earth.
A correction in addition to the secondary phase factor correction for the additional time or phase delay for transmission of a low frequency signal over a composite land-water path when the signal transit time is based on the free-space velocity.
Referring to a thermodynamic change of state of a system in which there is no transfer of heat or mass across the boundaries of the system. In an adiabatic process, compression causes warming, expansion causes cooling. Two angles having a common vertex and lying at opposite ends of a common side.
The determination and application of corrections to observations, for the purpose of reducing errors or removing internal inconsistencies in derived results. Pertaining to the body of law that governs maritime affairs. Afloat and unattached to the shore or the sea bottom, and without propulsive power.
To move forward, as to move a line of position forward, parallel to itself, along a course line to obtain a line of position at a later time. A line of position which has been moved forward along the course line to allow for the run since the line was established.
Transport of atmospheric properties solely by mass motion of the atmosphere. A type of fog caused by the advection of moist air over a cold surface, and the consequent cooling of that air to below its dew point. SEA FOG is a very common advection fog that is caused by moist air in transport over a cold body of water.
A radiobeacon established for use by both mariners and airmen. Of or pertaining to the operation or navigation of aircraft. A visual aid to navigation, displaying flashes of white or colored light or both, used to indicate the location of airports, landmarks, and certain points of the Federal airways in mountainous terrain and to mark hazards. A luminous or lighted aid to navigation intended primarily for air navigation.
A radiobeacon whose service is intended primarily for aircraft. The corresponding adjectives for fall, winter, and spring are autumnal, hibernal and vernal. A stream flowing into a larger stream or lake; a tributary. Floating on the water; water-borne. Near, toward, or at the stern of a craft. The slowly decaying luminescence of the screen of the cathode-ray tube after excitation by an electron beam has ceased.
A broad, high arch of radiance or glow seen occasionally in the western sky above the highest clouds in deepening twilight, caused by the scattering effect of very fine particles of dust suspended in the upper atmosphere. A ridge of ice forced up by pressure which has undergone considerable weathering. The time interval between the maximum semimonthly north or south declination of the moon and the maximum effect of the declination upon the range of tide or the speed of the tidal current; this effect is manifested chiefly by an increase in the height or speed difference between the two high low waters or flood ebb currents during the day.
The time interval between perigee of the moon and the maximum effect of parallax upon the range of tide or the speed of the tidal current. The time interval between new or full moon and the maximum effect of these phases upon the range of tide or the speed of the tidal current.
The elapsed time, usually expressed in days, since the last new moon. A divided triangle method of sight reduction in which a perpendicular is dropped from the GP of the body to the meridian of the observer.
Rear Admiral Arthur A. Ageton, USN, inventor of the Ageton method. A line joining points of no magnetic variation, a special case of an isogonic line. Of or pertaining to a condition of no gravitation.
Resting or lodged on the bottom. A generally southwestward flowing ocean current of the Indian Ocean, one of the swiftest ocean currents. To the south of South Africa the greatest volume of its water bends sharply to the south and then toward the east, thus returning to the Indian Ocean.
The distance traveled by a vessel proceeding ahead at full power from the time the engines are reversed until she is at full stop. The condition of a vessel making no way in a storm, allowing wind and sea to determine the position of the ship. Sailing vessels lying ahull lash the helm alee, and may carry storm sails. A device or structure external to a craft, designed to assist in determination of position, to define a safe course, or to warn of dangers or obstructions. If the information is transmitted by light waves, the device is called a visual aid to navigation; if by sound waves, an audible aid to navigation; if by radio waves; a radio aid to navigation.
Any aid to navigation using electronic equipment, whether or not radio waves are involved, may be called an electronic aid to navigation. A periodical publication of astronomical data designed primarily for air navigation, but often used in marine navigation.
Air Almanac, a joint publication of the U. Naval Observatory and H. In general the information is similar to that of the Nautical Almanac, but is given to a precision of 1' of arc and 1s of time, at intervals of 10m values for the sun and Aries are given to a precision of 0.
Airspace of defined dimensions within which the ready identification location, and control of aircraft are required. An extensive body of air with fairly uniform horizontal physical properties, especially temperature and humidity.
In its incipient stage the properties of the air mass are determined by the characteristics of the region in which it forms.
It is a cold or warm air mass if it is colder or warmer than the surrounding air. Air masses are classified according to their source regions.
Latitude and Longitude (Meridians and Parallels)
Four such regions are generally recognized- 1 equatorial Ethe doldrum area between the north and south trades; 2 tropical Tthe trade wind and lower temperate regions, 3 polar Pthe higher temperate latitudes; and 4 Arctic or Antarctic Athe north or south polar regions of ice and snow.
This classification is a general indication of relative temperature, as well as latitude of origin. Air masses are further classified as maritime m or continental cdepending upon whether they form over water or land. This classification is an indication of the relative moisture content of the air mass. A third classification sometimes applied to tropical and polar air masses indicates whether the air mass is warm w or cold k relative to the underlying surface.
The w and k classifications are primarily indications of stability, cold air being more stable. A correction due to nonstandard air temperature, particularly the sextant altitude correction due to changes in refraction caused by difference between the actual temperature and the standard temperature used in the computation of the refraction table.
Refraction is greater at lower temperatures, and less at higher temperatures. The correction for air temperature varies with the temperature of the air and the altitude of the celestial body, and applies to all celestial bodies, regardless of the method of observation. It is not applied in normal navigation. It is the northward flowing division of the Aleutian Current.
The ratio of radiant energy reflected to that received by a surface, usually expressed as a percentage; reflectivity. The term generally refers to energy within a specific frequency range, as the visible spectrum.
Its most frequent application in navigation is to the light reflected by a celestial body. Computations of times and-altitudes of available satellite passes in a given period of time at a given location, based on orbital data transmitted from satellite memory. A plant of simple structure which grows chiefly in water, such as the various forms of seaweed. It ranges in size from a microscopic plant, large numbers of which sometimes cause discoloration of water, to the giant kelp which may extend for more than feet in length.
A defined procedure or routine used for solving a specific mathematical problem. The part of an optical measuring instrument comprising the optical system, indicator, vernier, etc. In modern practice the term is used principally in connection with a bearing circle fitted with a telescope to facilitate observation of bearings.
To place objects in line. The placing of objects in a line. The process of orienting the measuring axes of the inertial components of inertial navigation equipment with respect to the coordinate system in which the equipment is to be used. A formula relating the illuminance produced on a normal surface at a given distance from a point source of light, the intensity of the light, and the degree of transparency of the atmosphere, assumed to be uniform. Designed or equipped to perform by day or night under any weather conditions.
A periodical publication of ephemeral astronomical data. If information is given in a form and to a precision suitable for marine navigation, it is called a nautical almanac. See also nautical almanac; if designed primarily for air navigation, it is called an air almanac. A small circle on the celestial sphere paralleled to the horizon. An ancient instrument formerly used for amplitude observations. An alloy composed principally of aluminum, nickel, cobalt, and iron; used for permanent magnets.
Up in the rigging of a ship. Referring to a set of computer characters consisting of alphabetic and numeric symbols. An electric current that continually changes in magnitude and periodically reverses polarity.
Referring to periodic changes in color of a lighted aid to navigation. A fixed light varied at regular intervals by a single flash of greater luminous intensity, with color variations in either the fixed light or flash, or both. A fixed light varied at regular intervals by a group of two or more flashes of greater luminous intensity, with color variations in either the fixed light or flashes or both.
A light showing a single flash with color variations at regular intervals, the duration of light being shorter than that of darkness. A group flashing light which shows periodic color change. A group occulting light which shows periodic color change. A light totally eclipsed at regular intervals, the duration of light always being longer than the duration of darkness, which shows periodic color change. A light showing different colors alternately. Angular distance above the horizon; the arc of a vertical circle between the horizon and a point on the celestial sphere, measured upward from the horizon.
Angular distance below the horizon is called negative altitude or depression. Altitude indicated by a sextant is called sextant altitude. Sextant altitude corrected only for inaccuracies in the reading instrument, index, and personal errors, as applicable and inaccuracies in the reference level principally dip is called apparent or rectified altitude.
After all corrections are applied, it is called corrected sextant altitude or observed altitude. An altitude taken directly from a table, before interpolation, is called tabulated altitude.
After interpolation, or if determined by calculation, mechanical device, or graphics, it is called computed altitude.
If the altitude of a celestial body is computed before observation, and sextant altitude corrections are applied with reversed sign, the result is called precomputed altitude. The difference between computed and observed altitudes corrected sextant altitudesor between precomputed and sextant altitudes, is called altitude intercept or altitude difference. An altitude determined by inexact means, as by estimation or star finder, is called an approximate altitude.
The altitude of a celestial body on the celestial meridian is called meridian altitude. The expression exmeridian altitude is applied to the altitude of a celestial body near the celestial meridian, to which a correction is to be applied to determine the meridian altitude. A parallel of altitude is a circle of the celestial sphere parallel to the horizon, connecting all points of equal altitude.
An azimuth determined by solution of the navigational triangle with altitude, declination, and latitude given. A time azimuth is computed with meridian angle, declination, and latitude given. A time and altitude azimuth is computed with meridian angle, declination, and altitude given. The change in the altitude of a celestial body occurring with change in declination, latitude, or hour angle, for example the first difference between successive tabulations of altitude in a latitude column of Pub.
The difference in minutes of arc between the computed and the observed altitude corrected sextant altitudeor between precomputed and sextant altitudes.
It is labeled T toward or A away as the observed or sextant altitude is greater or smaller than the computed or precomputed altitude. As defined by the International Telecommunication Union ITUthe altitude of the apogee above a specified reference surface serving to represent the surface of the earth. As defined by the International Telecommunication Union ITUthe altitude of the perigee above a specified reference surface serving to represent the surface of the earth.
A prefix used in cloud classification to indicate the middle level. Clouds within the middle level mean height 6, 20, ft. These elements are arranged in groups, in lines, or waves, following one or two directions, and are sometimes so close together that their edges join. A sheet of gray or bluish cloud within the middle level mean height 6, ft. Sometimes the sheet is composed of a compact mass of dark, thick, gray clouds of fibrous structure; at other times the sheet is thin and through it the sun or moon can be seen dimly.
Abbreviation for Ante Meridian; before noon in zone time. The temperature of the air or other medium surrounding an object. In navigation, the condition obtained when a given set of observations defines more than one point, direction, line of position, or surface of position. Having two or more possible meanings or values. American Ephemeris and Nautical Almanac. American Practical Navigator, The. At, near, or toward the middle of a ship. The derived unit of magnetic field strength in the International System of Units.
Point on a tidal chart where the cotidal lines meet. An area surrounding a no-tide point from which the radiating cotidal lines progress through all hours of the tidal cycle. An increase in signal magnitude from one point to another, or the process causing this increase. Of a transducer, the scalar ratio of the signal output to the signal input.
A device which enables an input signal to control power from a source independent of the signal and thus be capable of delivering an output which is greater than the input signal. Angular distance of a celestial body north or south of the prime vertical circle; the arc of the horizon or the angle at the zenith between the prime vertical circle and a vertical circle through the celestial body measured north or south from the prime vertical to the vertical circle.
38º 42' N - 09º 25' W
The term is customarily used only with reference to bodies whose centers are on the celestial horizon, and is prefixed E or W, as the body is rising or setting, respectively; and suffixed N or S to agree with the declination. The prefix indicates the origin and the suffix the direction of measurement. Amplitude is designated as true, magnetic, compass, or grid as the reference direction is true, magnetic, compass, or grid east or west, respectively.
The maximum value of the displacement of a wave, or other periodic phenomenon, from the zero position. One-half the range of a constituent tide. By analogy, it may be applied also to the maximum speed of a constituent current. A compass intended primarily for measuring amplitude. Seldom used on modern vessels. Distortion occurring in an amplifier or other device when the output amplitude is not a linear function of the input amplitude.
The process of changing the amplitude of a carrier wave in accordance with the variations of a modulating wave. Operated by the U. Coast Guard, the Amver System is a maritime mutual-assistance program that aids coordination of search and rescue efforts by maintaining a worldwide computerized DR plot of participating vessels. Any wind blowing up an incline. A graduated scale of the declination of the sun and the equation of time for each day of the year located in the Torrid Zone on the terrestrial globe.
A computer in which quantities are represented by physical variables. Problem parameters are translated into equivalent mechanical or electrical circuits as an analog for the physical phenomenon being investigated without the use of a machine language.
An analog computer measures continuously; a digital computer counts discretely. An area where vessels may anchor, either because of suitability or designation. A nautical chart showing prescribed or recommended anchorages.
A navigation mark which indicates an anchorage area or defines its limits. A device used to secure a ship to the sea floor. To use the anchor to secure a ship to the sea floor. If more than one anchor is used the ship is moored. A buoy marking the position of an anchor on the bottom, usually painted green for the starboard anchor and red for the port anchor, and secured to the crown of the anchor by a buoy rope.
Submerged ice attached or anchored to the bottom, irrespective of the nature of its formation. A light shown from a vessel or aircraft to indicate its position when riding at anchor. An instrument for measuring the speed of the wind. Some instruments also indicate the direction from which it is blowing. An instrument which determines atmospheric pressure by the effect of such pressure on a thin-metal cylinder from which the air has been partly exhausted.
A radar echo caused by a physical phenomenon which cannot be seen. The inclination to each other of two intersecting lines, measured by the arc of a circle intercepted between the two lines forming the angle, the center of the circle being the point of intersection. Any angle not a multiple of 90 is an oblique angle.
Two adjacent angles have a common vertex and lie on opposite sides of a common side. A dihedral angle is the angle between two intersecting planes.
A spherical angle is the angle between two intersecting great circles. The smaller angular difference of two bearings or lines of position. The angle in a vertical plane between the horizontal and a descending line. The angle through which a ray is bent by refraction. The angle in a vertical plane between the horizontal and an ascending line, as from an observer to an object.
The angle between the line of motion of a ray of radiant energy and the perpendicular to a surface, at the point of impingement. The angle between the line of motion of a ray of reflected radiant energy and the perpendicular to a surface, at the point of reflection.
The angle between a refracted ray and the perpendicular to the refracting surface. The angle between the transverse axis of a craft and the horizontal.
The horizontal angle of the region of indefinite characteristic near the boundaries of a sector of a sector light. A unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a micron or one hundred millionth of a centimeter.
Of or pertaining to an angle or angles. The angular difference between two directions, numerically equal to the angle between two lines extending in the given directions. The arc of the great circle joining two points, expressed in angular units. Distance between two points, expressed in angular units of a specified frequency.
Distortion in a map projection because of non-conformity. The quantity obtained by multiplying the moment of inertia of a body by its angular speed. Time rate of change of angular displacement of the earth relative to the fixed stars equal to 0.
Change of direction per unit time. To heat to a high temperature and then allow to cool slowly, for the purpose of softening, making less brittle, or removing permanent magnetism. When Flinders bars or quadrantal correctors acquire permanent magnetism which decreases their effectiveness as compass correctors, they are annealed.
Any marking on illustrative material for the purpose of clarification such as numbers, letters, symbols, and signs. Of or pertaining to a year; yearly. Seasonal variation in water level or tidal current speed, more or less periodic due chiefly to meteorological causes. An eclipse in which a thin ring of the source of light appears around the obscuring body. Annular solar eclipses occur, but never annular lunar eclipses.
A positive electrode; the plate of a vacuum tube; the electrode of an electron tube through which a principal stream of electrons leaves the inter-electrode space. The positive electrode of an electrochemical device, such as a primary or secondary cell, toward which the negative ions are drawn.
Pertaining to the periodic return of the moon to its perigee, or of the earth to its perihelion. The average period of revolution of the moon from perigee to perigee, a period of 27 days, 13 hours, 18 minutes, and The secular variation does not exceed a few hundredths of a second per century. The interval between two successive passes of a satellite through perigee. The period of one revolution of the earth around the sun, from perihelion to perihelion, averaging days, 6 hours, 13 minutes, Departure from the strict characteristics of the type, pattern, scheme, etc.
An angle used in the mathematical description of the orbit of one body about another. It is the angle between the radius vector of the body and the line of apsides and is measured from pericenter in the direction of motion. When the radius vector is from the center of the primary to the orbiting body, the angle is called true anomaly.
When the radius vector is from the center of the primary to a fictitious body moving with a uniform angular velocity in such a way that its period is equal to that of the actual body, the angle is called mean anomaly.
When the radius vector is from the center of the elliptical orbit to the point of intersection of the circle defined by the semimajor axis with the line perpendicular to the semimajor axis and passing through the orbiting body, the angle is called eccentric anomaly or eccentric angle.
Departure of the local mean value of a meteorological element from the mean value for the latitude. The region within the Antarctic Circle, or, loosely, the extreme southern regions of the earth.
A type of air whose characteristics are developed in an Antarctic region. The semi-permanent, semi-continuous front between the Antarctic air of the Antarctic Continent and the polar air of the southern oceans; generally comparable to the arctic front of the Northern Hemisphere.
The obliteration of contrast between surface features in the Antarctic when a covering of snow obscuring all landmarks is accompanied by an overcast sky, resulting in an absence of shadows and an unrelieved expanse of white, the earth and sky blending so that the horizon is not distinguishable.
Before noon, or the period of time between midnight and noon A structure or device used to collect or radiate electromagnetic waves. A combination of antennas with suitable spacing and with all elements excited to make the radiated fields from the individual elements add in the desired direction, i.
The complete equipment associated with an antenna, including, in addition to the antenna, the base, switches, lead-in wires, revolving mechanism, etc. The generated bearing of the antenna of a radar set, as delivered to the indicator. A radio-frequency transformer used to connect an antenna to a transmission line or to connect a transmission line to a radio receiver. A radio-frequency transformer, link circuit, or tuned line used to transfer radio-frequency energy from the final plate-tank circuit of a transmitter to the transmitter to the transmission line feeding the antenna.
A spurious effect, in a loop antenna, resulting from the capacitance of the loop to ground. The component of an antenna of mirror or lens type that irradiates, or receives energy from, the mirror or lens. A diffraction phenomenon very similar to but complementary to the corona, appearing at a point directly opposite to the sun or moon from the observer. An approximately circular portion of the atmosphere, having relatively high atmospheric pressure and winds which blow clockwise around the center in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
An anticyclone is characterized by good weather. The winds associated with a high pressure area and constituting part of an anticyclone. It flows along the northern side of the Greater Antilles. The number corresponding to a given logarithm. Either of the two points on an orbit where a line in the orbit plane, perpendicular to the line of nodes, and passing through the focus, intersects the orbit. Anything exactly opposite to something else. The prevailing western winds which blow over and in the opposite direction to the trade winds.
The pink or purplish zone of illumination bordering the shadow of the earth in the dark part of the sky opposite the sun after sunset or before sunrise. Heavy cumulus or cumulonimbus having an anvil-like upper part. The point of the orbit of one member of a double star system at which the stars are farthest apart.
Without a period; of irregular occurrence. An opening; particularly, the opening in the front of a camera through which light rays pass when a picture is taken. The diameter of the objective of a telescope or other optical instrument, usually expressed in inches, but sometimes as the angle between lines from the principal focus to opposite ends of a diameter of the objective.
Of a directional antenna, that portion of nearby plane surface that is perpendicular to the direction of maximum radiation and through which the major part of the radiation passes. An antenna in which the beam width is determined by the dimensions of a horn, lens, or reflector. The ratio of the diameter of the objective to the focal length of an optical instrument.
Do parallels and meridians intersect at right angles
The highest point of something, as of a cone or triangle, or the maximum latitude vertex of a great circle. That point in the elliptical orbit of a body about the sun farthest from the sun.
A map projection which is neither conformal nor equal area. In an elliptical orbit, the point in the orbit which is the farthest distance from the focus, where the attracting mass is located. The apocenter is at one end of the major axis of the orbital ellipse. Time Zones The meridians are also useful for designating time zones. Noon is the time when the Sun is directly above a meridian; to the west of that meridian is forenoon, to the east is afternoon.
This makes a difference of exactly 1 hour between each zone. In the United States, there are four time zones. The dividing lines are somewhat irregular because communities near the boundaries often find it more convenient to use time designations of neighboring communities or trade centers.
Figure shows the time zones in the United States. When the Sun is directly above the 90th meridian, it is noon Central Standard Time. At the same time, it will be 1 p. Eastern Standard Time, 11 a. Mountain Standard Time, and 10 a. These time zone differences must be taken into account during long flights eastward—especially if the flight must be completed before dark.
Remember, an hour is lost when flying eastward from one time zone to another, or perhaps even when flying from the western edge to the eastern edge of the same time zone.
In most aviation operations, time is expressed in terms of the hour clock. Air traffic control instructions, weather reports and broadcasts, and estimated times of arrival are all based on this system.
Because a pilot may cross several time zones during a flight, a standard time system has been adopted. All of the time zones around the world are based on this reference. To convert to this time, a pilot should do the following: Measurement of Direction By using the meridians, direction from one point to another can be measured in degrees, in a clockwise direction from true north. To indicate a course to be followed in flight, draw a line on the chart from the point of departure to the destination and measure the angle which this line forms with a meridian.
Direction is expressed in degrees, as shown by the compass rose in figure Because meridians converge toward the poles, course measurement should be taken at a meridian near the midpoint of the course rather than at the point of departure.
The course measured on the chart is known as the true course. This is the direction measured by reference to a meridian or true north. It is the direction of intended flight as measured in degrees clockwise from true north. The true heading is the direction in which the nose of the airplane points during a flight when measured in degrees clockwise from true north.
Usually, it is necessary to head the airplane in a direction slightly different from the true course to offset the effect of wind. Consequently, numerical value of the true heading may not correspond with that of the true course.
The American Practical Navigator/Glossary
This will be discussed more fully in subsequent sections in this chapter. For the purpose of this discussion, assume a no-wind condition exists under which heading and course would coincide. To use the compass accurately, however, corrections must be made for magnetic variation and compass deviation. Variation Variation is the angle between true north and magnetic north. It is expressed as east variation or west variation depending upon whether magnetic north MN is to the east or west of true north TNrespectively.
If the Earth were uniformly magnetized, the compass needle would point toward the magnetic pole, in which case the variation between true north as shown by the geographical meridians and magnetic north as shown by the magnetic meridians could be measured at any intersection of the meridians. Actually, the Earth is not uniformly magnetized.
In the United States the needle usually points in the general direction of the magnetic pole, but it may vary in certain geographical localities by many degrees.
Consequently, the exact amount of variation at thousands of selected locations in the United States has been carefully determined. The amount and the direction of variation, which change slightly from time to time, are shown on most aeronautical charts as broken magenta lines, called isogonic lines, which connects points of equal magnetic variation.