Latitude and Longitude (Meridians and Parallels)
) there is given an investigation ofthe angle VVMZ, between the true the velocity of the ship will he a maximum when the angle WMZ is a right angle, or who; take place on the two hows if her movement were in the direction of her keel, the terrestrial meridians and parallels of latitude were straight lines respectively. In a line approximately at right angle to the ship's keel opposite the waist or middle part of a ship. See also The convergence to different foci, by a lens or mirror, of parallel rays of light. .. The Red Sea owes its name to red algae, as does the “red tide.” . Point on a tidal chart where the cotidal lines meet. At right angles to the keel of the boat, but not on the boat. . A term used to describe the vessel which must yield in meeting, crossing or overtaking The maximum speed a hull can achieve without planing. A mark or permanent line on a compass indicating the direction forward parallel to the keel when properly installed.
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 American Practical Navigator/Glossary
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.
The American Practical Navigator/Glossary - Wikisource, the free online library
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. 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.
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.
The line connecting points at which there is no variation between true north and magnetic north is the agonic line. An isogonic chart is shown in figure Minor bends and turns in the isogonic and agonic lines are caused by unusual geological conditions affecting magnetic forces in these areas. Magnetic meridians are in black, geographic meridians and parallels are in blue. Variation is the angle between a magnetic and geographic meridian. On the west coast of the United States, the compass needle points to the east of true north; on the east coast, the compass needle points to the west of true north.
Zero degree variation exists on the agonic line which runs roughly through Lake Michigan, the Appalachian Mountains, and off the coast of Florida, where magnetic north and true north coincide. This conversion is made by adding or subtracting the variation which is indicated by the nearest isogonic line on the chart.
The true heading, when corrected for variation, is known as magnetic heading. The black lines are isogonic lines which connect geographic points with identical magnetic variation. Remember, to convert true course or heading to magnetic course or heading, note the variation shown by the nearest isogonic line.
If variation is west, add; if east, subtract. To determine compass heading, a correction for deviation must be made. Because of magnetic influences within the airplane such as electrical circuits, radio, lights, tools, engine, magnetized metal parts, etc. This deflection is deviation. The deviation is different for each airplane, and it also may vary for different headings in the same airplane.
For instance, if magnetism in the engine attracts the north end of the compass, there would be no effect when the plane is on a heading of magnetic north.
Do parallels and meridians intersect at right angles
Minutes of latitude have a very special place in the art of navigation. One minute of latitude is defined as one nautical mile. A nautical mile corresponds to a little more than a statute mile. If we know latitude, as it is written on the sides of a nautical chart, then we have a very handy and easy way to measure distance.
This works on mercator projection charts which are the norm for navigation see later. Taking this just a bit further we define our speed in knots; One knot equals one nautical mile per hour. In the image at left we see the north and south poles, the equator, and lines of longitude. Lines of longitude or meridians are lines that run from the north pole to the south pole. Longitude forms the other set of coordinates so we can now define every spot on Earth by specifying both latitude and longitude.
Longitude is measured from the meridian that runs through Greenwich, England. We call the line of longitude that runs through Greenwich the Prime Meridian. We can also call any line of longitude a meridian. We specify longitude in a similar fashion to latitude.