Definition
The speed at which light and all other electromagnetic waves (radio waves, radar signals, GPS signals) travel through a vacuum. Its value is approximately 186,000 miles per second, or 300,000 kilometers per second (more precisely, 299,792,458 meters per second). It is a universal physical constant, denoted by the symbol c.
Plain English
How fast light and radio signals travel — about 186,000 miles every second. Nothing travels faster.
Context Anchor
Seen in discussions of radio navigation, radar, satellite navigation, and any system that measures distance by timing a signal.
Derivation
The phrase comes from physics. Here, “light” does not mean only visible light; it refers more broadly to electromagnetic energy, which includes radio, radar, and satellite signals used in aviation.
Why Pilots Care
Most modern navigation aids (GPS, DME, radar, VOR, transponders) work by measuring the time radio waves take to travel between two points. Because those waves travel at the speed of light, very small timing differences translate into precise distances and positions.
Grounding Statement
If you flipped a switch in New York, the light would reach Los Angeles in about 1/60th of a second. Radio signals to and from a satellite take roughly the same amount of time.
Intuition Check
Do not read “light” as only what you see with your eyes. In this context, radio, radar, and satellite signals follow the same basic speed rule.
Example Sentence 1
GPS receivers calculate position by measuring how long satellite signals take to arrive, knowing they travel at the speed of light.
Example Sentence 2
GPS receivers adjust for the brief time radio waves need to cover the distance from satellite to aircraft at the speed of light.