| Planet | Average distance from the Sun (miles) | Light travel time |
|---|---|---|
| Mercury | 35,977,392 | 3 minutes 13 seconds |
| Venus | 67,232,363 | 6 minutes 1 seconds |
| Earth | 92,957,130 | 8 minutes 19 seconds |
| Mars | 141,672,632 | 12 minutes 41 seconds |
| Jupiter | 483,737,473 | 43 minutes 17 seconds |
| Saturn | 889,803,547 | 1 hour 19 minutes |
| Uranus | 1,781,471,207 | 2 hours 39 minutes |
| Neptune | 2,805,490,932 | 4 hours 11 minutes |
| Pluto | 3,670,066,808 | 5 hours 28 minutes |
Light travel time from Earth
Because every world is at a different distance on different days, the time a radio signal or a flash of light takes to reach Earth changes too. The Moon is 1.4 seconds away at its farthest, and Mars is between 3 minutes 2 seconds and 22 minutes 19 seconds away.
| World | At the closest | At the farthest |
|---|---|---|
| The Moon | 1.2 seconds | 1.4 seconds |
| The Sun | 8 minutes 11 seconds | 8 minutes 27 seconds |
| Venus | 2 minutes 7 seconds | 14 minutes 31 seconds |
| Mars | 3 minutes 2 seconds | 22 minutes 19 seconds |
| Jupiter | 32 minutes 43 seconds | 53 minutes 51 seconds |
| Saturn | 1 hour 7 minutes | 1 hour 32 minutes |
| Pluto | 3 hours 58 minutes | 6 hours 58 minutes |
Light travel time for any distance
To see these times for real destinations, use the travel time calculator.
Light has a speed limit
In a vacuum light travels at 299,792,458 meters per second, or 299,792 km/s. That number is exact, because the meter is defined from it: the International Bureau of Weights and Measures fixes the speed of light and defines the meter as the distance light covers in 1/299,792,458 of a second. It wasn't always known that light has a speed at all. In 1676 the Danish astronomer Ole Romer, who had been timing eclipses of Jupiter's moon Io, showed that light takes time to travel. His estimate for how long sunlight takes to reach Earth was too long, but it was in the right range.
The real figure is 8 minutes 19 seconds. Sunlight takes 5 hours 28 minutes to reach Pluto at its average distance, as in the table above.
Why delays matter in space
Every radio signal travels at the speed of light, so every conversation with a spacecraft has a delay. The Moon is 2.4 to 2.7 seconds away for a round trip. Mars is between 6 and 45 minutes. That gap is why rovers have to drive themselves, and why a mission controller only ever sees what happened a few minutes ago. For Mars specifically, see the Mars travel page.
The farthest messenger
NASA says Voyager 1 is on the brink of reaching a distance of one light-day from Earth. Its signals take almost a day to arrive, and commands to it take as long. Its own story is in the Voyager 1 page.
Stars are measured in light years
A light year is the distance light covers in a year, 9,460,730,472,581 km. The nearest star, Proxima Centauri, is 4.2465 light years away, so the light you would see from it left more than four years ago. What that means for travel is covered in the nearest star travel page, and the same distances as a street-sized model are on the scale page.
A few answers worked out
Using the distances from the NASA fact sheet and the exact speed of light, light takes: 1.3 seconds to reach the Moon, at its average distance; 8 minutes 19 seconds to reach the Sun; 3 minutes 2 seconds to reach Mars at its closest; 32 minutes 43 seconds to reach Jupiter at its closest; 1 hour 7 minutes to reach Saturn at its closest; 5 hours 28 minutes to reach Pluto at its average distance. These are the same figures the calculator gives when you pick each destination.
Light years and light days
A light year is 9,460,730,472,581 km. A light day is 25,902,068,371 km, and a light hour is 1,079,252,849 km. The nearest star is 4.2465 light years away, which is 1,551 light days.
A call to the Moon
A signal to the Moon and back takes 2.42 seconds at the closest distance and 2.71 at the farthest. That's the short pause you would notice if you could speak to someone there, a gap of well over a second.