Signal / Light Travel Time Calculator
Calculate how long light or radio signals take to travel any distance in space — from the Moon to distant galaxies.
Travel Time
Light and all electromagnetic signals (radio, X-ray, etc.) travel through space at the same speed:
c = 299,792.458 km/s
Travel time formula:
t = d / c
This means there is an unavoidable delay in any communication or observation across space. When you look at the Sun, you see it as it was 8.3 minutes ago. When scientists on Earth send a command to a Mars rover, it takes 3 to 22 minutes one way, depending on where Mars is in its orbit.
Key distances and light travel times:
- Earth to Moon (384,400 km): 1.28 seconds
- Earth to Sun (149.6 million km / 1 AU): 8.32 minutes
- Earth to Mars at closest (54.6 million km): 3.03 minutes
- Earth to Mars at average (225 million km): 12.5 minutes
- Earth to Mars at farthest (401 million km): 22.3 minutes
- Earth to Jupiter at average (628 million km): 34.9 minutes
- Earth to Neptune at average (4.4 billion km): 4.1 hours
- Earth to Pluto at average (5.9 billion km): 5.5 hours
- Earth to Proxima Centauri (4.24 light-years): 4.24 years
- Earth to Andromeda Galaxy (2.537 million ly): 2.537 million years
The light-year defined: One light-year is the distance light travels in exactly one Julian year (365.25 days). It equals 9.461 × 10¹² km, or about 63,241 AU.