Quick Answer
Compass declination changes throughout the year due to the Earth's slightly ellipsoidal shape and the tilt of its magnetic axis. This variation can be significant in areas far from the equator. Compass declination shifts about 30-40 minutes per year.
Understanding Compass Declination
Compass declination, also known as magnetic declination, is the angle between magnetic north and true north. It varies depending on your location and the time of year. In areas close to the magnetic equator, declination is close to zero, while in areas far from the equator, it can be quite large.
Declination Shifts
The Earth’s magnetic field is not fixed, and it shifts over time due to changes in the Earth’s core. This shift affects compass readings, requiring a correction to determine true north. The declination shift is usually around 30-40 minutes per year, meaning a compass declination of 10 degrees will shift to 10.25 degrees in 12 months. For example, in the town of Juneau, Alaska, the declination in 2020 was about 25.5 degrees east. By 2022, it had shifted to about 24.5 degrees east.
Calculating Declination
To determine declination, you can use online resources such as the US Geological Survey (USGS) website, which provides declination values for different locations. These values are usually updated annually. You can also use a declination map or consult with a local expert. It’s essential to understand declination and make necessary corrections when using a compass to determine direction.
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