How does the earth’s magnetic field affect compass readings?

Magnetic Declination and Variation

Magnetic declination is the angle between magnetic north and true north. It varies depending on the location, and a compass user needs to know the local declination to adjust the reading. For example, if the magnetic declination is 10 degrees east, the compass needle will point 10 degrees east of true north. A compass user can find the local declination by consulting a map or a declination chart. In the United States, the declination can range from 20 to 30 degrees, and it can change over time due to the movement of the Earth’s magnetic field.

Understanding the Compass Needle

A compass needle is a magnetized piece of metal that aligns itself with the Earth’s magnetic field. The needle has two ends, a north pole and a south pole, and it always points towards the magnetic north pole. The compass user needs to understand the behavior of the needle to accurately read the compass. The needle will deviate from the true north direction due to the Earth’s magnetic field, and the user needs to adjust the reading accordingly. For example, if the compass needle points to a rock, it means that the rock is north of the user’s location.

Adjusting for Magnetic Variation

To adjust for magnetic variation, a compass user needs to know the local declination and the direction of the declination. If the declination is east, the user needs to add the declination to the compass reading to get the true north direction. If the declination is west, the user needs to subtract the declination from the compass reading. For example, if the compass reading is 30 degrees and the declination is 10 degrees east, the user needs to add 10 degrees to get the true north direction, which is 40 degrees. A compass user needs to be familiar with the local magnetic variation to navigate accurately.