Electromagnetic Wave Speed in Vacuum

Overview

Electromagnetic waves include radio waves, microwaves, infrared waves, visible light, ultraviolet light, X-rays, and gamma rays.
These waves all share the common property of moving at the speed of light in vacuum, denoted by the symbol “c”.
Unlike mechanical waves, electromagnetic waves can propagate through empty space (vacuum).

The speed of light in vacuum is a universal physical constant, approximately 299,792 kilometers per second.
This high value implies that electromagnetic waves, when in a vacuum, can cross significant distances in microscopic amounts of time.
The speed of light in vacuum, c, is always the same, regardless of the observer’s velocity or that of the light source.

All electromagnetic waves propagate through a vacuum at the speed of light, c.
This means that whether they are X-rays, visible light or radio waves, they move at the same speed if they are in a vacuum.
However, when these waves enter a different medium (like glass or water), their speed changes due to the phenomenon of refraction.
The speed at which the different types of electromagnetic waves travel in other media depends on the medium’s refractive index.

The constant speed of light in a vacuum allows for calculated estimations regarding large cosmic distances, often described in light-years.
The speed of electromagnetic waves in a vacuum becomes crucial in technologies such as GPS and communications satellites, where precise timing is required.
Lastly, the concept of the speed of light being constant in all inertial (non-accelerating) frames of reference forms one of the two postulates of Einstein’s Special Theory of Relativity.