Latitude & longitude; Learn about the earth's coordinate system.
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. Understanding how these angles relate to each other can help you figure out how Parallel lines never meet, and perpendicular lines intersect at a right angle. In a line approximately at right angle to the ship's keel- opposite the waist or .. celestial sphere parallel to the horizon, connecting all points of equal altitude.
Abbreviation for Ante Meridian; before noon in zone time. The temperature of the air or other medium surrounding an object.
Latitude and Longitude (Meridians and Parallels)
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.
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. 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. The average semidiurnal range of the tide occurring at the time of apogean tides. It is smaller than the mean range, where the type of tide is either semidiurnal or mixed, and is of no practical significance where the type of tide is diurnal.
Tidal currents of decreased speed occurring monthly as the result of the moon being at apogee farthest from the earth. Tides of decreased range occurring monthly as the result of the moon being at apogee farthest from the earth. That orbital point of a non-circular orbit farthest from the center of attraction.
Apparent altitude is used in obtaining a more accurate refraction correction than would be obtained with an uncorrected sextant altitude. Motion relative to a specified or implied reference point which may itself be in motion. The expression usually refers to movement of celestial bodies as observed from the earth. Apparent noon may be either local or Greenwich depending upon the reference meridian. High noon is local apparent noon. The position on the celestial sphere at which a celestial body would be seen if the effects of refraction, diurnal aberration, and geocentric parallax were removed; the position at which the object would actually be seen from the center of the earth.
Apparent change in the direction of the axis of rotation of a spinning body, such as a gyroscope, due to rotation of the earth. As a result of gyroscopic inertia or rigidity in space, to an observer on the rotating earth a gyroscope appears to turn or precess. Technically, it is frequently defined as the slope of a least-squares line of regression through a relatively long series of yearly mean sea level values.Longitude and Latitude - reading lesson for kids
The word apparent is used since it is often not possible to know whether a trend is truly non periodic or merely a segment of a very long oscillation. A line drawn on the chart in lieu of the mean high water line or the mean water level line in areas where either may be obscured by marsh, mangrove, cypress, or other marine vegetation. This line represents the intersection of the appropriate datum with the outer limits of vegetation and appears to the navigator as the shoreline.
The duration of one rotation of the earth on its axis, with respect to the apparent sun. It is measured by successive transits of the apparent sun over the lower branch of a meridian. The length of the apparent solar day is 24 hours of apparent time and averages the length of the mean solar day, but varies somewhat from day to day.
The actual sun as it appears in the sky. Time based upon the rotation of the earth relative to the apparent or true sun.
This is the time shown by a sun dial. Apparent time may be designated as either local or Greenwich, as the local or Greenwich meridian is used as the reference.
The speed and true direction from which the wind appears to blow with reference to a moving point. A computer program designed to do a specific task or group of tasks. A chart used to approach a harbor. An altitude determined by inexact means, as by estimation or by a star finder or star chart. The six coefficients used in the analysis of the magnetic properties of a vessel in the course of magnetic compass adjustment. The values of these coefficients are determined from deviations of an unadjusted compass.
The near approach of one celestial body to another on the celestial sphere, as in occultation, conjunction, etc. The penumbral eclipse of the moon.
On the sea floor a gentle slope, with a generally smooth surface, particularly as found around groups of islands or sea mounts. The area of wharf or quay for handling cargo. A sloping underwater extension of an iceberg. An outwash plain along the front of a glacier. Either of the two orbital points nearest or farthest from the center of attraction, the perihelion and aphelion in the case of an orbit about the sun, and the perigee and apogee in the case of an orbit about the earth.
A conduit or artificial channel for the conveyance of water, often elevated, especially one for the conveyance of a large quantity of water that flows by gravitation. A part of a curved line, as of a circle. The semi-circular graduated scale of an instrument for measuring angles. A squall which is relatively high in the center, tapering off on both sides. Consequently, numerical value of the true heading may not correspond with that of the true course.
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.
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. Provides a safety railing and serves as an attachment for the lifelines. Pushpit — Pulpit located on the stern. Quarter — The sides of a boat aft of amidships. Queen topsail — Small stay sail located between the foremast and mainmast. Reef points — A horizontal line of light lines on a sail which may be tied to the boom, reducing the area of the sail during heavy winds.
Rigging — The lines that hold up the masts and move the sails standing and running rigging. In a mainsail, the roach extends past the line of the leech between the head and the clew and is often supported by battens. Rope — In general, cordage as it is purchased at the store. When it comes aboard a vessel and is put to use it becomes line. Roller reefing — Reduces the area of a sail by rolling it around a stay, the mast, or the boom.
Most common on headsails. Rub-rail — Also rubbing strake or rub strake. An applied or thickened member at the rail, running the length of the boat; serves to protect the hull when alongside a pier or another boat. Rudder — A vertical plate or board for steering a boat. Run — To allow a line to feed freely.
Running backstay — Also runner, or preventive backstay. A stay that supports the mast from aft, usually from the quarter rather than the stern. When the boat is sailing downwind, the runner on the leeward side of the mainsail must be released so as not to interfere with the sail. Running rigging — The adjustable portion of the rigging, used to control sails and equipment. Running lights — Lights required to be shown on boats underway between sundown and sunup. Sailing Rig — The equipment used to sail a bost, including sails, booms and gaffs, lines and blocks.
Scandalize — On a gaff rig the sail is made loose footed, the clew is brought forward along the boom and the sail cloth is drawn up in folds along the gaff and mast. From this position the sail is instantly available for use. Schooner — Sailing ships with at least 2 masts foremast and mainmast with the mainmast being the taller. Scope — Technically, the ratio of length of anchor rode in use to the vertical distance from the bow of the vessel to the bottom of the water.
Usually six to seven to one for calm weather and more scope in storm conditions. Scupper — Drain in cockpit, coaming, or toe-rail allowing water to drain out and overboard. Seat Locker — A storage locker located under a cockpit seat. Seat locker — A storage locker located under a cockpit seat.
Self-tacking — Normally applied to a sail that requires no adjustment other than sheeting when boat is tacked Seamanship — All the arts and skills of boat handling, ranging from maintenance and repairs to piloting, sail handling, marlinespike work, and rigging. Sea Room — A safe distance from the shore or other hazards. Secure — To make fast.
Set — Direction toward which the current is flowing. Sheer — The line of the upper deck when viewed from the side. Normal sheer curves up towards the bow and stern. Reverse sheer curves down towards the bow and stern. Compound sheer, curving up at the front of the boat and down at the stern, and straight sheer are uncommon. Sheer Strake — The topmost planking in the sides, often thicker than other planking.
Sheets — Lines used to control the position of a sail. Ship — A larger vessel usually thought of as being used for ocean travel. Shroud — A line or wire running from the top of the mast to the spreaders, then attatching to the side of the vessel. Shrouds — Lateral supports for the mast, usually of wire or metal rod. Skeg — For sailboats, usually refers to a structural support to which the rudder is fastened.
Slab Reefing — Also points reefing, and sometimes jiffy reefing. Reduces the area of the mainsail by partially lowering the sail and resecuring the new foot by tying it to the boom with points, or light lines attached to the sail. Slack — Not fastened; loose. Sole — The floor of the cockpit or cabin. Sounding — A measurement of the depth of water. Spar — A pole or a beam. Spar Poles — Most often of wood, aluminum or carbon fiber, used as supports, such as the mast, boom, or spinnaker pole.
Spinnaker — A large, triangular sail, most often symmetrical, flown from the mast in front of all other sails and the forestay. Splashboard — A raised portion of the hull forward of the cockpit intended to prevent water entering. Spreaders — Also crosstrees.
Short horizontal struts extending from the mast to the sides of the boat, changing the upward angle of the shrouds. Spring Line — A pivot line used in docking, undocking, or to prevent the boat from moving forward or astern while made fast to a dock. May be adjusted during racing, in some classes. Stay — A line or wire from the mast to the bow or stern of a ship, for support of the mast fore, back, running, and triadic stays.
Stem — the timber at the very front of the bow. Strake — On wooden boats, a line of planking running from the bow to the stern along the hull. Squall — A sudden, violent wind often accompanied by rain. Square Knot — A knot used to join two lines of similar size. Also called a reef knot.
Standing Part — That part of a line which is made fast. The main part of a line as distinguished from the bight and the end. Starboard — The right side of a boat when looking forward.
Stern — The after part of the boat. Stow — To put an item in its proper place. Swamp — To fill with water, but not settle to the bottom. Tail is controlling, coiling, and securing the runnning end of the halyard. Tabernacle — A hinged mast step located on deck. Since it is hinged, the mast may be lowered easily. Tack — On a triangular sail, the bottom forward corner. Taffrail — The rail at the stern of the boat. In small boats, often used as a seat. Thwartships — At right angles to the centerline of the boat.
Tide — The periodic rise and fall of water level in the oceans. Slots allow drainage and the attachment of blocks. Topmast — A second spar carried at the top of the fore or main mast, used to fly more sail. Topping lift — A line or wire rope used to support the boom when a boat is anchored or moored.
Topsides — The sides of a vessel between the waterline and the deck; sometimes referring to onto or above the deck. Trampoline — The fabric support that serves for searing between the hulls of a catamaran. Trapeze — Wire gear enabling a crewmember to place all of his weight outboard of the hull, thus helping to keep the boat level. In many boats the traveler may be adjusted from side to side so that the angle of the sheets can be changed to suit conditions.
Trim — Fore and aft balance of a boat. Underway — Vessel in motion, not moored or aground. May have a cowl, which can be angled into or away from the wind; and may be constructed with baffles, so that water is not allowed below, as in Dorade ventilator.
Wake — Moving waves, track or path that a boat leaves behind it, when moving across the waters. May also be used to indicate moving warping a boat into position by pulling on a warp.
The American Practical Navigator/Glossary
Way — Movement of a vessel through the water such as headway, sternway or leeway. Wheel — Device used for steering a boat. Widow-maker — A term for the bowsprit many sailors lost their lives falling off the bowsprit while tending sails.
Windward — Toward the direction from which the wind is coming. Wishbone — A boom composed of two separate curved pieces, one on either side of the sail. With this rig, sails are usually self tending and loose-footed. Yacht — A pleasure vessel, a pleasure boat; in American usage the idea of size and luxury is conveyed, either sail or power.
Yankee — A fore-sail flying above and forward of the jib, usually seen on bowsprit vessels.