“Latitude, Longitude, Earth’s Magnetism and Compass Error” 52 RCACS Ground School Navigation PO 404 EO 2 “Latitude, Longitude, Earth’s Magnetism and Compass Error”

Introduction Teaching Points Review Reference: Longitude and Lattitude Time and Longitude Earth’s Magnetism Review Reference: FTGU Chapter 7 Section A Pages 175-182

Longitude and Lattitude MERIDIANS OF LONGITUDE Semi great circles joining the true (or geographic) poles of the earth. They are measured from 0 to 180 degrees East and West of the PRIME MERIDIAN, which runs through Greenwich, England. The meridian opposite the prime meridian (180) is called the INTERNATIONAL DATE LINE and here time changes a day. Meridians are measured in degrees, minutes and seconds. There are 60 minutes in a degree and 60 seconds in a minute.

Longitude and Lattitude (Cont’d) PARALLELS OF LATITUDE Circles on the earth's surface whose planes lie parallel to the equator. Latitude is measured from 0 to 90 degrees North and South of the EQUATOR , which is numbered 0 degrees. Parallels of Latitude are also expressed in degrees, minutes and seconds.

Time and Longitude SOLAR DAY - interval between two successive transits of the Sun( ie. If the sun appears overhead at noon, the next time the sun appears overhead at noon, a solar day will have gone by.) A solar day is divided into 24 hours. The sun travels once around the earth every day, so therefore it travels 360 degrees of longitude in one day. So, time can be expressed in terms of longitude.

Time and Longitude (Cont’d) Time to Longitude 24 hours = 360 degrees longitude 1 hours = 15 degrees longitude 1 min = 15 minutes longitude 1 sec = 15 seconds longitude Longitude to Time 360 degrees longitude = 24 hours 1 degree longitude = 4 min 1 minute longitude = 4 sec 1 second longitude = 1/15 sec

Earth’s Magnetism True North Magnetic north The north pole of the earth. Magnetic north The direction the compass needle lies without considering deviation and is not at a fixed position. The magnetic field of the earth changes as the magnetic north moves about in a circle.

Earth’s Magnetism (Cont’d) Magnetic Variation The angle between the true meridian and the magnetic meridian in which the compass needles lies, is called magnetic variation. Also known as magnetic declination. The technique for calculating magnetic heading is adding or subtracting the variation from the true heading. True Heading-East Variation=Magnetic Heading True Heading+West Variation=Magnetic Heading Helpful Reminder EAST IS LEAST WEST IS BEST

Magnetic Variation

Earth’s Magnetism (Cont’d) Compass Deviation The angle between the magnetic heading and the compass heading, which is the magnetic heading corrected for deviation. The technique for calculating compass heading is adding or subtracting the deviation from the magnetic heading. Magnetic Heading-East Deviation=Compass Heading Magnetic Heading+West Deviation=Compass Heading

Compass Deviation

Earth’s Magnetism (Cont’d) All variation and deviation can be remembered by: T true track V variation M magnetic heading D deviation C compass heading

Earth’s Magnetism (Cont’d) Compass Errors A compass has several errors which cause the compass to not point directly to magnetic north. These errors are overcome by the following acknowledgments of the errors. Magnetic Dip The magnetic lines of force are parallel to the earth near the equator, but become vertical near the magnetic poles. This makes the compass needle dip toward the surface of the earth at the higher latitudes making the compass unreliable. Northerly Turning Error When an aircraft banks so does the compass and this causes a small error. On turns from NORTH the compass LAGS. On turns from SOUTH the compass LEADS. One way to remember this is that the compass always wants to swing toward north. So when turning away it lags and when turning toward it leads. There is no error on turns from EAST or WEST headings.

Magnetic Inclination (DIP)

Earth’s Magnetism (Cont’d) Acceleration and Deceleration Error When speeding up or slowing down the compass tilts and on east or west headings this tilt makes the compass turn slightly. On east or west headings: ACCELERATION makes the compass turn NORTH. DECELERATION makes the compass turn SOUTH. Helpful Reminder: A acceleration N north D deceleration S south There is no error when accelerating or decelerating on north or south headings.

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