---
title: "Light Travel Time Calculator: Moon to Stars | Orbit Whisper"
description: "How long light and radio take from Earth to the Moon, the Sun, each planet and the nearest stars: closest, farthest and today, plus any distance you enter."
url: https://orbitwhisper.buzz/light-travel-time/
---

299,792 km every second

# Light travel time

Nothing outruns light, and radio is light too. See how long a signal takes from Earth to the Moon, the Sun, each planet and the nearest stars: at the closest, at the farthest and on any date you choose.

## Reading the delays

Every time here is distance divided by the speed of light in a vacuum, exactly 299,792.458 km/s. Radio, the way we talk to spacecraft, travels at the same speed. Planets move round the Sun at different rates, so their distance from us swings between a **closest** approach, when they line up on our side of the Sun, and a **farthest**, when they sit behind it.

The **on this date** column places each planet with JPL's approximate orbital elements, good to a few seconds of light time between 1800 and 2050. The Moon and Pluto show their range only, and the stars are so far away that the time is simply their distance in light-years, counted in years.

Tick **round trips** for how long you wait between asking a question and hearing an answer. With Mars at least 3 minutes away, and up to 22, rovers have to drive themselves between instructions.

Light delay, closer to home

Light in glass fibre moves at about two-thirds of its speed in space, so even an undersea cable across the Atlantic adds tens of milliseconds each way. Curious what your own connection looks like? [WebTraceCheck's free network self-check](https://webtracecheck.com/network-check) shows your IPv4 and IPv6 addresses, DNS resolver and WebRTC details.

## Sources

- Closest and farthest distances from Earth: the individual [NASA Planetary Fact Sheets](https://nssdc.gsfc.nasa.gov/planetary/factsheet/), including the [Moon](https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html) (mean perigee and apogee) and the [Sun](https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html).
- Planet positions on a date: E. M. Standish, [Approximate Positions of the Planets](https://ssd.jpl.nasa.gov/planets/approx_pos.html), JPL Solar System Dynamics, Table 1 (1800–2050).
- Star distances from trigonometric parallaxes in RECONS, The One Hundred Nearest Star Systems (Research Consortium On Nearby Stars, recons.org, list as of 1 January 2012).
- Speed of light: [NIST reference on constants](https://physics.nist.gov/cgi-bin/cuu/Value?c). Astronomical unit, 149,597,870.7 km: IAU 2012 Resolution B2. Light-year: c × 365.25 days.

## Questions and answers

**Does sunlight really take eight minutes to reach us?**

Yes. At the average distance of one astronomical unit it takes 499 seconds, 8 minutes 19 seconds. In early January, when Earth is closest, it is about 8 minutes 11 seconds; in early July about 8 minutes 27 seconds.

**Could you have a phone call with someone on Mars?**

Not a normal one. Each reply would wait at least 6 minutes for the round trip, and up to about 45 minutes when Mars is on the far side of the Sun, so messages would work more like letters.

**Why does Pluto's range overlap Neptune's?**

Pluto's orbit is stretched and tilted. For 20 years of each 248-year circuit it is closer to the Sun than Neptune, which last happened from 1979 to 1999, so its closest distance from Earth is slightly less than Neptune's farthest.

**Why is the starlight table a single number?**

Earth's yearly orbit changes a star's distance by only a few light-minutes out of light-years, far too little to show. Light from Proxima Centauri left it about 4.24 years before you see it.