At the speed of light to Neptune: about 4.2 hours
At the speed of light (1,079,252,849 km/h) it would take about 4.2 hours to get to Neptune – at the average distance of 4.5 billion km, non-stop and in a straight line.
Because the distance keeps changing, the travel time ranges from 4 hours (closest) to 4.3 hours (farthest).
For comparison
During the 1989 Neptune flyby, radio commands to Voyager 2 travelled about four hours – an answer came back after eight hours at the earliest.
How it is calculated
- Closest distance
- 4.3 billion km
- Average distance
- 4.5 billion km
- Farthest distance
- 4.69 billion km
- Speed
- 1,079,252,849 km/h
- Formula
- Travel time = distance ÷ speed
- Result
- 4.5 billion km ÷ 1,079,252,849 km/h ≈ 4.2 hours
Assumption: constant speed in a straight line, with no stops, acceleration or braking. Real spacecraft fly curved paths and use the gravity of planets.
Good to know: Neptune
Neptune is the outermost planet and in 1846 became the first planet found by calculation rather than by observation. It is about 30 times as far from the Sun as Earth and needs 165 years for one orbit. Only one spacecraft has ever visited it: Voyager 2 in 1989.
→ Fact sheet: Neptune