Light Travel Time Calculator
Enter a distance and its unit to find how long light takes to cross it. Light moves at 299,792,458 metres per second, so even nearby space spans minutes.
How to use the light travel time calculator
- Enter the distance you want light to cross.
- Pick the unit: kilometres, AU, light years, parsecs or miles.
- Read the travel time in seconds, minutes, hours, days and years.
Examples
Sunlight reaching Earth
distance = 1 AU
about 499 seconds, roughly 8.32 minutes
Light from the Moon
distance = 384,400 km
about 1.28 seconds
Frequently asked questions
How long does light take to reach Earth from the Sun?
About 499 seconds, or roughly 8.32 minutes, since the Sun sits about one astronomical unit (1 AU) away from Earth.
What is the light travel time formula?
Time equals distance divided by the speed of light, t = d / c, where c is 299,792,458 metres per second. The distance is first converted to metres.
Why does one light year equal one year of travel time?
A light year is defined as the distance light covers in one Julian year, so dividing it by the speed of light returns exactly one year.
What is a parsec in travel time?
One parsec is about 3.26 light years, so light needs roughly 3.26 years to cross it. The tool also reports the result in days and hours.
Does light travel time account for an expanding universe?
No. This is a simple distance divided by speed in a vacuum. For very distant galaxies, cosmological expansion makes lookback time more involved.
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