Quick Answer
The Earth's magnetic field influences compass navigation by affecting the compass needle's alignment, causing it to deviate from true north. This deviation is known as declination, and it varies depending on the location and time. Compass users must take this into account to achieve accurate navigation.
Understanding Declination
Declination is the difference between magnetic north and true north, and it varies depending on the location. In the Northern Hemisphere, declination is positive, meaning the compass needle points east or west of true north. In the Southern Hemisphere, declination is negative, meaning the compass needle points west or east of true north. For example, in the United States, the declination in 2023 ranges from 10 degrees west to 20 degrees east, varying by location.
Measuring and Compensating for Declination
To compensate for declination, compass users can use a declination chart or app. For example, the USGS Declination Calculator provides a declination value for a given location. Users can also adjust their compass by rotating it to align the direction-of-travel arrow with the desired bearing, taking into account the declination value.
Using a Compass in the Field
When using a compass in the field, it’s essential to take declination into account to avoid navigation errors. Here are some tips: always use a declination chart or app to determine the local declination value. Adjust your compass accordingly, and double-check your bearing by using other navigation tools, such as a GPS device or a map.
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