Land NavigationLand NavigationTerm: Magnetic DeclinationTerm: Magnetic Declination

Website: Website: http://www.ngdc.noaa.gov/http://www.ngdc.noaa.gov/Go to “Geomagnetic Data”Go to “Geomagnetic Data”

Go to “Declination”Go to “Declination”Go to “Compute your declination”Go to “Compute your declination”

(N38(N38°, W77°)°, W77°)What is the declination for Warrenton?What is the declination for Warrenton?What was it on this day in 1994? 1974?What was it on this day in 1994? 1974?

Magnetic DeclinationMagnetic Declination►The number of degrees that a The number of degrees that a

compass needle is pulled away from compass needle is pulled away from True North to point toward Magnetic True North to point toward Magnetic North North

Declination DiagramDeclination Diagram

Magnetic FluxMagnetic Flux► The Earth’s Magnetic Field is NOT The Earth’s Magnetic Field is NOT

stationarystationary

► You need current map or use a declination You need current map or use a declination chart or websitechart or website

Warrenton 1994 DiagramWarrenton 1994 Diagram► - True North – the top of - True North – the top of

the earththe earth►GN – Grid North – 1GN – Grid North – 1°° 45’ 45’►MN – Magnetic North – 10MN – Magnetic North – 10°°

GNMN

Declination for WarrentonDeclination for Warrenton►2009= 102009= 10°9’°9’►1994= 9°54’1994= 9°54’►1974= 7°47’1974= 7°47’

Why do we need to know all this?

► So that we can navigate using a mapmap, the ground ground and compasscompass.

► You cannot follow a GN with a compass; nor can you plot a MN with a protractor. To assist you in making the conversion from MN to GN, and vice versa, a declination diagram is placed on the map margin.

► When using a mapmap - use a protractor to measure GRIDGRID Bearings. Do not use the compass magnetic needle.

► When using the groundground – use a CompassCompass to Measure MAGNETIC MAGNETIC Bearings.

From groundground to mapmap.1. You measure the bearing of a landmark on the

ground with a compass. It is 321° MN. 2. The G-M ANGLE on the Map is 10°3. So MN to GN ADD 321°+ 10° = 331°331° GN

Draw this angle on your map

From mapmap to groundground.1. You measure the bearing of a point on the map with

a protractor. It is 331°331° GN. 2. The G-M ANGLE on the Map is 10° 3. So GN to MN SUBTRACT 331331°- 10° = 321° MN

Put this on your compass

Map Information – DirectionCONVERSION for Western Declination

Warrenton 1994 DiagramWarrenton 1994 Diagram► - True North – the top of - True North – the top of

the earththe earth►GN – Grid North – 1GN – Grid North – 1°° 45’ 45’►MN – Magnetic North – 10MN – Magnetic North – 10°°► IF you read 90° (east) on IF you read 90° (east) on

your map, what should your your map, what should your compass reading be to walk compass reading be to walk directly east?directly east?

GNMN

Remember which North you are Remember which North you are using!using!

►On your map decide if you will use:On your map decide if you will use: The True North (Outside border lines)The True North (Outside border lines) The Grid North (The inside grid lines)The Grid North (The inside grid lines)

►Use the Magnetic to Grid or Magnetic Use the Magnetic to Grid or Magnetic to True conversionto True conversion

How to Orient a Map How to Orient a Map 1.1. Find the declination diagram in the map's Find the declination diagram in the map's

margin. Note the degree.margin. Note the degree.2.2. Line up one of the long sides of the compass Line up one of the long sides of the compass

with one of the map's north-south margins. with one of the map's north-south margins. Make sure the direction of travel arrow on Make sure the direction of travel arrow on the compass points to north on the map. the compass points to north on the map.

3.3. Rotate map and compass until the magnetic Rotate map and compass until the magnetic needle of the compass points to the number needle of the compass points to the number of degrees the magnetic north is to the right of degrees the magnetic north is to the right or left of map north.or left of map north.

Types of CompassesTypes of Compasses►Military LensaticMilitary Lensatic

►Baseplate CompassBaseplate Compass

►Thumb CompassThumb Compass

Thumb Loop

Lanyard Ring

Sighting Slot

Lens

Luminous Bezel LineLuminous Magnetic Arrow

Fixed Index Line

Luminous Heading

Luminous Sighting Dots

Sighting Wire

Graduated Straight Edge

Floating DialBezel

1. COVER 2. BASE

3. LENS REAR SITE

LENSATIC COMPASS PARTS and Features of a Lensatic compass

PART 1 Basic Land NavigationBasic Land Navigation

Degrees – common unit of measure is the degree (º).

• 360 Degrees to a Circle• Distance Between Red Marks = 5º• Distance Between Big Marks = 10º• Distance Between Red Numbers = 20º

N = 0ºE = 90º

S = 180ºW = 270º

BLACK RING

RED RING

FLOATING DIAL SCALEFLOATING DIAL SCALEMils - is used mainly in artillery, tank, and mortar gunnery. AND is also used for very accurate azimuth land navigation.• 6400 Mils to a Circle• Distance Between Small Marks = 20 Mils• Distance Between Big Marks = 100 Mils• Distance Between Numbers = 200 Mils

N = 64 (6400)E = 16 (1600)S = 32 (3200)W = 48 (4800)

8.89 Mils = ½ Degree17.78 Mils = 1 Degree

PART 1 Basic Land NavigationBasic Land Navigation

SIGHTING A LENSATIC COMPASS

PART 1 Basic Land NavigationBasic Land Navigation

SIGHTING A LENSATIC COMPASS

PART 1 Basic Land NavigationPART 1 Basic Land Navigation

SIGHTING A LENSATIC COMPASSPART 1 Basic Land NavigationBasic Land Navigation

SIGHTING A LENSATIC COMPASSPART 1 Basic Land NavigationBasic Land Navigation

65° AZIMUTH(11.5m = 1,150mils)

SIGHTING A LENSATIC COMPASSPART 1 Basic Land NavigationBasic Land Navigation

What ifWhat if►You wanted to hike from the hill 700 You wanted to hike from the hill 700

west of the hort building to the tower west of the hort building to the tower on View Tree Road. What map on View Tree Road. What map azimuth do you measure?azimuth do you measure?

►What would your compass reading be?What would your compass reading be?

Handout MapHandout MapAnswer in your notebookAnswer in your notebook

1.1. How far is it on Rt 678 from where Lower How far is it on Rt 678 from where Lower Waterloo Rd splits off & remeets 678.Waterloo Rd splits off & remeets 678.

2.2. What is the 6 digit coord. for the Hort Bdg?What is the 6 digit coord. for the Hort Bdg?3.3. What terrain feature is found at 526 905?What terrain feature is found at 526 905?4.4. What terrain feature is found at 553 919?What terrain feature is found at 553 919?5.5. What is the elevation at Fauquier High School?What is the elevation at Fauquier High School?6.6. What is the elevation of Fauquier Hospital?What is the elevation of Fauquier Hospital?