Answer:The mean declination, which refers to the angle between true north and magnetic north, changes over time because the Earth's magnetic field is not constant and is subject to changes and fluctuations over time.
The Earth's magnetic field is generated by the motion of molten iron in the Earth's outer core. This motion is affected by a variety of factors, including the Earth's rotation, the movement of the continents, and the convective motion of the molten iron. These factors can cause the magnetic field to shift and change over time.
In addition, the Earth's magnetic field undergoes periodic reversals, during which the north and south magnetic poles switch places. The most recent reversal occurred about 780,000 years ago, and the next one could occur at any time. These reversals can also cause changes in the mean declination over time.
Another factor that can affect the mean declination is the location of the observer on the Earth's surface. The magnetic field varies in strength and direction depending on the observer's location, so the mean declination will be different at different locations on the Earth's surface.
Overall, the mean declination changes over time due to the complex and dynamic nature of the Earth's magnetic field, as well as other factors such as the location of the observer.
Step-by-step explanation: