What is variation in terms of navigation?

In navigation, variation refers to the angular difference between true north and magnetic north. This distinction is essential because navigators utilize both true and magnetic reference frames to plot courses and ensure accuracy in navigation. True north is the direction along the earth's surface towards the geographic North Pole, while magnetic north is where a magnetic compass points, which can be influenced by local magnetic anomalies and the Earth's magnetic field. Understanding the variation allows navigators to convert between compass headings and true headings, ensuring safe and precise navigation, especially over long distances.

The other choices focus on different aspects of navigation that do not directly relate to the concept of variation. Distance traveled versus the forecasted distance deals with distance measurement and planning accuracy, while the time taken to reach a destination pertains to travel speed and duration—both important navigational elements but not related to variation. Lastly, the change in heading over time relates to route dynamics rather than the fundamental difference between true and magnetic north, which is the essence of variation.