Beginner Map Reading Compass. Compass Parts of a Compass.

Presentation on theme: "Beginner Map Reading Compass. Compass Parts of a Compass."— Presentation transcript:

Compass

Parts of a Compass

FInstrument used to show direction FPoints to the Magnetic North Pole FMaps are generally printed with north up  USGS topographic maps show GN, MN and H FGN is Grid North – the north of the map grid FMN is Magnetic North – where the compass points  H is True North – geographic north, the northern end of the north-south axis of the Earth FThe difference between True North and Magnetic North is magnetic declination FDeclination changes with time as indicated on the map, but the rate of change is not constant Compass

Position of the Magnetic North Pole in different years

Find this on your map TN MN

Declination MN vs. TN On the day the map was printed

FWhat is the declination on your map? FCurrent magnetic declination near Crested Butte is F10° 20’ E, changing by 0° 7’ West per year FDeclination is important when converting between map (true or grid) and compass (magnetic) azimuths FAzimuth is the angle measured from north in a clockwise direction (0° north, 90 ° east, 180° south, 270° west) Declination

Declination 10 o 20’ E As of July 1, 2009 From Crested Butte

We will round off to 10 for this presentation Please copy the formulas

Using Compass and Maps Understanding how to use declination Using a map and compass to find your location Although it’s not the perfect terminology, we will use the words bearing and azimuth interchangeably in this presentation

I drew a line from my home in CB So. to the top of Round Mt I measured the angle using a protractor = 150 o

I then lined up my compass with Round Mt and read the compass It showed 160 o I plotted the 160 o on the map and the result is shown here The difference in the two lines is the declination If I traveled using 150 o without adjusting for D. I’d miss by ½ mile

Calculate the Magnetic Baring Use the formula to calculate the Magnetic Baring we should enter on the compass Once we calculate the MB of 140 o we look at 140 o and see it’s lined up with the top of Round Mt The 140 o was drawn on this map to show you what a TN plot of 140 would look line

If the declination was W, you would use this formula

End of Compass Section 3 - A Next section Section continues with 3 – B