Final answer:
A line marked on the compass in a ship or aircraft, showing the direction straight ahead is known as the lubber line.
Compasses provide orientation by aligning with Earth's magnetic field and are essential for navigation at sea or in the air. Compass bearings are also used to express specific directions.
Step-by-step explanation:
When navigating, a crew member aligns a lubber line with the chosen course, using the compass to maintain the ship or aircraft on a steady heading. Compasses are crucial navigation tools that align with Earth's magnetic field, pointing towards magnetic north.
Mariners also use compass bearings to denote a specific direction, expressed as a three-digit number based on the compass rose, such as 053°, which indicates a direction slightly northeast.
Different compass types vary in their design and functionality, but all serve the fundamental purpose of displaying orientation relative to Earth's magnetic poles. Some advanced compasses can compensate for the difference between magnetic north and true north.
Navigation relies heavily on accurately knowing the direction, which can involve the use of a sextant for celestial navigation, particularly 'shooting the Sun' to determine latitude.