What is the speed of light?
Quick Answer
Light travels at exactly 299,792,458 meters per second in a vacuum — about 1.08 billion km/h. One light-year equals 9.46 trillion km, and sunlight takes 8 minutes 20 seconds to reach Earth.
The Full Story
The speed of light in a vacuum (denoted "c") is exactly 299,792,458 m/s — a universal constant defined by physics. At this speed, light could circle Earth's equator 7.5 times per second. One light-year — the distance light travels in one year — is 9.461 trillion km. Sunlight takes about 8 minutes 20 seconds to reach Earth from 150 million km away. Nothing with mass can reach or exceed this speed according to Einstein's special relativity. In media like glass or water, light slows down (to about 200,000 km/s in glass), which is why prisms split white light into a rainbow.
Key Facts
YouTube Angle
Suggested video title for this topic:
"How Fast is Light REALLY? — Visualizing 299 Million Meters Per Second"