You blink for about 0.3 seconds. In that instant, how far has light traveled?
A typical human blink lasts about 0.3 to 0.4 seconds. In that time, light travels about 100,000 kilometers. That's enough to circle the Earth 2.5 times. The Moon is 384,400 km away — light makes it there in 1.28 seconds, about three blinks.
In one second — three blinks — light travels 300,000 km. In one hour, 1.08 billion km. In one year, 9.46 trillion km. That's a light-year. The nearest star is 4.24 light-years away. If you blinked right now, the light from that star left 4.24 years ago, and it's still arriving.
The point isn't that light is fast. The point is that the distances are so enormous that even the fastest thing we know takes years to cross them. The universe isn't just big. It's so big that it takes light — the speed limit of everything — hours, years, or centuries to get from one place to another. Every night sky is a time machine. You're seeing everything as it was when the light left.
About 0.3 to 0.4 seconds. In that time, light travels about 100,000 km. That's 2.5 trips around the Earth.
300,000 km. From Earth to the Moon and back is about 768,800 km, so light makes a round trip to the Moon in about 2.6 seconds.
Light itself. Nothing in the universe can travel faster. The expansion of space can appear faster, but that's not matter moving — that's space itself stretching.
Light travels at exactly 299,792,458 meters per second. That's fast enough to circle the Earth 7.5 times in one second. In the time it takes you to blink, light has already crossed distances that feel absurd.
Next time you blink, remember: while your eyes were closed, light raced past the Moon, bounced off your wall, and was already somewhere else entirely.