Light Travel Time
Calculator
Results
- Light travel time (seconds)
- 1.28222
- Light travel time (minutes)
- 0.02137
- Light travel time (hours)
- 0.000356
Astronomy results
| Light travel time (seconds) | 1.28222 |
| Light travel time (minutes) | 0.02137 |
| Light travel time (hours) | 0.000356 |
formula-map diagram
- Light travel time (seconds)
- 1.28222
- Light travel time (minutes)
- 0.02137
- Light travel time (hours)
- 0.000356
Astronomical relationship
Formula
t = d / c= 1.2822203819417
Note
This result is a simplified model: it applies the displayed textbook formula to the values you entered, assuming ideal spherical bodies, circular orbits, blackbody radiation and perfect optics, and ignoring atmospheric seeing, relativistic corrections beyond those stated, cosmological models and measurement uncertainty. Use published ephemerides and catalogue data for real observations.
More in Astronomy and space
See all →Frequently asked questions
What does light travel time tell me about an object I'm observing?+
It tells you how long light took to reach you, meaning you are seeing the object as it was in the past, not as it is now. For a star 100 light-years away, you're seeing light that left it a century ago.
How is light travel time calculated from a distance?+
The calculator divides the distance by the speed of light, about 299,792 km/s, converting the result into convenient units like seconds, minutes, or years depending on the scale. Distance in light-years is actually already a time-based unit in disguise, since it's defined as the distance light covers in one year.
Why does sunlight take about 8 minutes to reach Earth?+
The Sun is about 150 million km away, and dividing that by the speed of light gives roughly 499 seconds, or about 8 minutes 19 seconds. This means if the Sun vanished, we would still see it shining for another 8 minutes.
Is light travel time the same as how far away an object 'looks'?+
Not exactly for very distant objects — over cosmological distances, the expansion of the universe means the simple distance-divided-by-speed-of-light calculation is only a good approximation. For nearby objects like stars in our galaxy, this straightforward method is accurate.
Could a star I see tonight have already exploded or disappeared?+
Yes, and this is one of the more striking implications of light travel time. Since light from a star 500 light-years away left it 500 years ago, that star could have gone supernova at any point since then and we wouldn't know until that new light arrives.