Hello and welcome to this lesson of the online course Wilderness Navigation Course.
What we will see:
- Talk again about the geographic and magnetic Norths
- The declination between them
- How to orient your compass to the geographic north.
Magnetic declination:
Like I’ve said before, the red needle of your compass aim at the magnetic north and not the geographic north, and as you see in this photo, they are not at the same spot.
If we are here at this place of earth, they will be a difference, and this difference is what we call the magnetic declination. It’s an angle measured in degrees East or West. For example, a declination of 10° West.
When the magnetic declination is west, it means that the magnetic north is west to the geographic north. And when the magnetic declination is east, the magnetic north is located East to the geographic north.
The earth’s magnetic field is in a constant movement throughout the years, so when you give a certain place a magnetic declination value, you have to add the date or the year to that.
- For example, a declination of 10° West in 2016.
Magnetic declination diagram:
This is a magnetic declination diagram that I did take from a USGS digital topographic map.
This star symbol shows the direction of the grid north.
Do you still remember when I’ve told you, in a previous lesson, that there are three Norths, and to keep things simple I will talk only about two? This is the third one.
This MN here stands for Magnetic North, and the GN stands for Geographic North (or True North).
So, at the center of this map, between the Magnetic North and the Grid North, there is an angle of 8° 42 Minutes East.
And between the Geographic North and the Grid North, there is an angle of 17 Minutes West.
Don’t worry about the Mils, because it’s just a measurement unit used by the military.
If we move to this declination diagram from my National Geographic Trails Illustrated topographic map. The first thing we see is that there is only the grid north and the Magnetic north, we don’t see the Geographic north, because the angle between it and the grid north is so little, so they ignore it.
Here, the approximate declination is 9 degrees in the year 2016, and the approximate annual change is 6 minutes West.
Orient your compass to the geographic north:
Now that we brought back some information that we’ve already seen, plus new ones about the grid north, we will learn how to orient a compass to the geographic north, and when I say that, I mean how to orient the direction of travel arrow to the geographic north.
Tip:
Before I show you how to orient your compass to the geographic north, I want you to know that there are chances that you forget to count the declination when you are orienting your compass.
For that, my tip for you is to stick two little lines of duct tape on the back of your compass to mark your declination.
For example, if I know that I will be outdoor in an area with a declination of 20° West, my final product will be like that.
With that, any time you have to put the red in the shed, as they say, you should put it between these two little black lines of duct tape.
You will see how to do that in a second.
What how to orient your compass to the geographic north (skip to 3:57):
Now let’s go for my question.
In this diagram, the magnetic declination is East or West?
In this exercise, I want you to :
- Orient your compass to the geographic north with a magnetic declination of 10° Est
- Take a picture of your work
- Put it for us in the comment section below.
That’s all for this lesson, do not forget that you can interact with the other members in the comment section below if you have any question or to just say hello.
Thank you and see you in the next lesson.