Light Lab
Light is fast. Space is big. Compare a distance with the time light needs to cross it.
Your light-speed comparison
In a vacuum, light travels at exactly 299,792,458 meters per second. These calculations use that speed and ignore matter, gravity, and cosmic expansion. A light-year is a distance, using a 365.25-day Julian year.
From our planet to another galaxy
| Journey or scale | Distance and travel time |
|---|---|
| An Earth-sized path | About 40,000 km 0.133426 seconds A straight path equal to roughly Earth’s circumference. Light does not naturally circle Earth. NASA Goddard source |
| Earth to Moon | Average distance: 384,400 km 1.28222 seconds A one-way vacuum calculation using the average distance; the Moon’s actual distance changes. NASA source |
| Sun to Earth | About 150 million km 500.346 seconds An approximate one-way calculation using a rounded Sun–Earth distance. NASA source |
| Andromeda to Earth | About 2.5 million light-years 2,500,000 years A scale estimate using distance divided by vacuum light speed, not a cosmological distance model. NASA / Hubble source |
Compare two journeys
Original schematic, not to scale. Move the slider with arrow keys to explore progress; this is not a real-time animation. The same fraction of the distance takes the same fraction of the travel time.
Sources and precision
NIST’s SI definition supplies the exact vacuum speed. The International Astronomical Union defines the light-year using a Julian year. NASA examples above are approximate, so more displayed digits do not make the distances exact. Sources reviewed .