Earth to Moon in 1.28 s
A photon takes about 1.28 seconds to go from Earth to the Moon—and back in about 2.56 s.
Lunar ping
Light Travel Distance
Inputs
Enter duration of a blink, shutter, or any tiny interval.
1 ms = 1,000 µs. We convert to seconds for the calculation.
Results
Distance (meters)
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Distance (km)
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Distance (miles)
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Earth–Moon fraction
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1 = Earth→Moon (~384,400 km).
AU fraction
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1 AU ≈ 149,597,870 km.
Times around Earth
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Earth circumference ≈ 40,075 km.
Speed of light (vacuum): 299,792,458 m/s. Atmosphere changes it slightly; we ignore that for simplicity.
5 Fun Facts about Light Speed
Fiber is slower
In fiber, light crawls at ~2/3 c. A 75 ms ping across oceans can be mostly glass-time, not routers.
Glass lag
Sunlight is old
Core photons random-walk for thousands of years before escaping the Sun, then only ~8 minutes to reach Earth.
Solar journey
Laser rangefinding
Lidar gear often times light over nanoseconds to measure distance—the same idea, just way faster.
Time-of-flight
Blink and it’s gone
A 300 ms blink lets light travel about 89,937 km—more than twice around Earth.
Blink distance
Why tiny times make for huge light distances
Light’s speed is so extreme that everyday slices of time translate into enormous distances. In vacuum, c ≈ 299,792,458 m/s. That’s roughly 300 meters in a microsecond and 300 kilometers in a millisecond. A typical 300 ms blink gives light enough time to loop Earth more than twice. This calculator turns those micro- and millisecond intuitions into concrete numbers across scales you know: meters, kilometers, miles, and handy space yardsticks like the Earth–Moon distance and the astronomical unit (AU).
The math is the simplest motion equation: d = c × t. The only tricky bit is unit handling. A microsecond is one-millionth of a second; a millisecond is one-thousandth. We always convert to seconds, multiply by c, and then express the result in multiple units. Dividing by 384,400 km gives the Earth–Moon fraction; dividing by 149,597,870 km gives the AU fraction; dividing by ~40,075 km shows how many times light could wrap Earth’s equator. Seeing the same distance in multiple lenses helps bridge human-scale timing to planetary and solar-system scales.
Light actually slows in media: in fiber it travels about two-thirds of its vacuum speed because glass has a higher index of refraction. That’s why global internet latency can’t beat the physics of glass, even with perfect routing. In air, the slowdown is smaller, so for a classroom-friendly model we keep vacuum speed. Relativity and gravitational effects are also out of scope here—at blink-length times, d = c × t is the right level of detail.
A useful learning angle is how linear changes in time scale distances. Halving your input halves every output. Doubling it doubles them. Yet the reference landmarks (Earth loop, Moon, AU) jump quickly, so tiny time tweaks push you across big narrative milestones. Another angle is latency: if you wait 50 ms for a page load, light could have crossed ~15,000 km in vacuum in that interval. That visualization makes the “speed of light limit” on global communication tangible.
Try plugging in camera shutter speeds, computer ping times, or sensor cycle times. Swap between microseconds and milliseconds to see how fast the numbers balloon. The distances aren’t just trivia—they connect everyday timing to cosmic scale in one line of math.