How is the heading of an aircraft determined in a compass?

The heading of an aircraft is determined by the alignment of the magnetic compass with the Earth's magnetic field. A magnetic compass functions based on the principle that a magnetized needle aligns itself with the Earth's magnetic field lines, which allows the pilot to read the magnetic heading of the aircraft. The compass provides a direct indication of the aircraft's orientation relative to magnetic north, which pilots can use for navigation and situational awareness.

The other options do not directly relate to how an aircraft's heading is determined by a compass. GPS coordinates provide position information but do not indicate orientation. The speed of the aircraft does affect other flight dynamics but does not impact the heading measurement from a compass. Similarly, atmospheric pressure can influence altimeter readings but has no bearing on heading determination. Therefore, the magnetic compass aligns with the Earth's magnetic field to accurately indicate heading.