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Maps, Compasses, and Magnetic Declination

What Is Magnetic Declination?

Magnetic declination is like a difference in directions between two norths: true north and magnetic north. True north is the direction the Earth spins, and magnetic north is the direction a compass needle points. Sometimes these two norths don’t line up exactly.

You know the Earth has a big ball of liquid metal inside it, right? Well, that metal moving around creates a magnetic field. This magnetic field is not perfectly lined up with the Earth’s top, or true north. It kind of has a mind of its own and points in different directions depending on where you are.

Because of this, magnetic north and true north don’t match up in the same place. The distance between them is called magnetic declination. It can be positive or negative, depending on whether magnetic north is to the right or left of true north.

The amount of magnetic declination changes depending on where you are on Earth and can even change over time. In some places, magnetic north and true north are pretty close, while in other places they’re far apart.

Why does this matter? Well, when you use a compass to find your way, you have to know the magnetic declination for your location. That way, you can adjust the compass reading to find true north. It’s like making a little correction to get the right direction.

But remember, magnetic declination is not the same everywhere, and it can change. So it’s a good idea to use updated maps or online sources to find the correct magnetic declination for your area.

How Is Declination Shown on Maps?

Imagine you have a map that shows directions. There are two kinds of north: true north, which is the top of the map and the direction the Earth rotates, and magnetic north, which is the direction a compass needle points towards.

The problem is that true north and magnetic north are not always in the same direction. Magnetic north can be a bit to the left or right of true north, depending on where you are on Earth. This difference in direction is called magnetic declination.

To show this on a map, they draw lines called isogonic lines. These lines connect places with the same magnetic declination. They have arrows that show where magnetic north points. The lines are labeled with numbers to tell you the angle between true north and magnetic north at different spots.

When you want to use a compass for navigation, you need to know the magnetic declination for your area. By looking at the isogonic lines on the map, you can figure out the approximate angle between true north and magnetic north where you are.

How Is Declination Used with a Compass?

When you use a compass, it helps you find your way by pointing towards magnetic north. But there’s a tricky part: the compass needle doesn’t point exactly to the true north, the direction maps show. This is because of something called magnetic declination.

Magnetic declination is like a difference in directions between magnetic north and true north. The compass points to magnetic north. The amount of declination can be different depending on where you are in the world.

So, to use a compass correctly, you need to make a small adjustment for the declination in your area. If you know the declination value, which you can find on maps or online, you can add or subtract that value from the compass reading to get the right direction.

For example, let’s say you’re using a compass and the declination in your area is 10 degrees to the east. If you want to go straight north according to your map, you need to turn the compass needle 10 degrees to the left (west) to account for the declination. That way, you’ll be heading in the true north direction.

By adjusting the compass for declination, you can follow the correct directions when hiking, exploring, or navigating in the outdoors.

Related Resources for Maps, Compasses, and Magnetic Declination

Unleashing Adventure: The Importance of Outdoor Skills in Scouting

In Scouting, outdoor adventures become even more amazing when Scouts learn how to use maps and compasses. It’s like having a superpower that helps them explore new places and find their way. By studying maps and mastering the compass, Scouts open the door to a world of exciting possibilities. They embark on a journey where they discover more about themselves, learn to overcome challenges, and become stronger and more confident individuals. It’s an adventure that leads to personal growth and reaching new heights!

orienteering troop program feature

Orienteering Troop Program Feature for Scouts BSA

Understanding magnetic declination is crucial for Scouts in the Orienteering troop program. Orienteering is all about finding markers on a map using a compass. By knowing about magnetic declination, Scouts can accurately interpret maps and align their compasses with true north. This knowledge becomes especially valuable when Scouts venture into different types of orienteering, like nighttime courses, paddling or horseback orienteering, cycling challenges, and even the exhilarating ROGAINE. Understanding magnetic declination empowers Scouts to confidently navigate these diverse orienteering experiences and make the most of their map and compass skills.

Orienteering Merit Badge

When Scouts are working on the Orienteering merit badge, they learn a lot about using maps and compasses to find their way. One important thing they discover is magnetic declination. It’s a fancy term that means the difference between the compass north and the true north on a map. Understanding this is really important for accurate navigation.

During their journey, Scouts study maps and learn to read the symbols and markings on them. They also learn how to find magnetic north and figure out the declination value. Armed with this knowledge, they can confidently take part in orienteering events. They get to test their skills by finding specific points on challenging courses. Knowing about magnetic declination helps them make precise adjustments and navigate accurately, making their orienteering experiences even better. They also develop a lifelong love for reading maps and using compasses.


3 responses to “Maps, Compasses, and Magnetic Declination”

  1. John Morgan Avatar
    John Morgan

    The difference between true north and magnetic north is called Variation. Declination is the angular height of a star above the celestial equator (analogous to latitude on the earth’s surface).

    1. Matt Kelly Avatar
      Matt Kelly

      In the military, we called it ‘deviation’. Indeed, declination and right ascencion are used to find the celestial position of stars.

      Variation was a number that had to be empirically tested and it was the amount of error contributed by the metal around the compass.

      We used the pneumonic “Can Dead Men Vote Twice, At Elections?”

      Compass +/- Deviation +/- Variation = Magnetic, (Add East)

  2. Garfield Avatar

    This excellent website certainly has all the info I
    wanted about this subject and didn’t know who to ask.

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