Voyager 1

// The Measure

What is a light day?

A light day is the distance light travels in 24 hours: 25,902,068,371 kilometres, about 173 times the distance from Earth to the Sun. Nothing physical waits at that line. No boundary, no dust, no change in the dark. The milestone belongs entirely to radio time. From 18 November 2026, a command sent to Voyager 1 takes a full day to arrive, and its reply takes another full day to come home. Say good morning on Monday and the answer lands on Wednesday.

For scale, here is how long a radio signal takes to reach some familiar places. The bars are on a logarithmic scale, because on a true scale the Moon's bar would be invisible.

// The Journey

Forty-nine years, one trajectory

Voyager 1 has not fired an engine to change course since its Saturn flyby in 1980. Everything since has been ballistic: one long, uninterrupted fall away from the Sun.

1. 20 August 1977

   Voyager 2 launches first

   The twins fly in reverse order. Voyager 2 lifts off from Cape Canaveral sixteen days before its sibling, on a slower trajectory built to reach all four giant planets.

2. 5 September 1977

   Voyager 1 launches

   On a faster route, Voyager 1 overtakes its twin within months. Each carries about 69 kilobytes of computer memory and a golden record bolted to its side.

3. 5 March 1979

   Jupiter

   Closest approach to Jupiter reveals erupting volcanoes on the moon Io: the first active volcanism ever seen beyond Earth, spotted in a navigation image.

4. 12 November 1980

   Saturn, and the last turn

   A close pass over the moon Titan bends the trajectory about 35 degrees up and out of the plane of the planets. It is the final course change Voyager 1 will ever make, and that 35 degree tilt is baked into the live distance maths at the top of this page.

5. 14 February 1990

   The Pale Blue Dot

   At Carl Sagan's urging, the cameras turn back one last time and photograph Earth from six billion kilometres: a fraction of a pixel in a sunbeam. The cameras are then switched off to save power.

6. 17 February 1998

   The most distant machine

   Voyager 1 overtakes Pioneer 10 to become the farthest human-made object in existence. It has held the record every day since.

7. 16 December 2004

   The termination shock

   The spacecraft crosses the region where the solar wind abruptly slows against interstellar gas: the first direct measurement of the heliosphere's inner boundary.

8. 25 August 2012

   Interstellar space

   Voyager 1 passes the heliopause and becomes the first spacecraft to sample the plasma between the stars, still calling home from beyond the Sun's protective bubble.

9. November 2017

   Thrusters wake after 37 years

   Backup attitude thrusters, dormant since 1980, fire perfectly on command. Engineers gain years of extra pointing ability from hardware built in the early 1970s.

10. 2023 to 2024

    The long-distance repair

    A failed memory chip garbles all telemetry into nonsense. Over five months, engineers relocate the affected code by radio, across a 45 hour round trip per exchange, and bring the science back online.

11. 2025 to 2026

    Powering down to stay alive

    The plutonium power source fades by about four watts a year. Instruments are switched off one by one so the transmitter can keep whispering home at 160 bits per second.

12. 18 November 2026

    One light day from Earth

    At 10:16:07 UTC, Voyager 1 becomes the first human-made object a full light day from home. The countdown above is running toward this exact second.

13. The far future

    Onward

    In about 40,000 years, Voyager 1 drifts within 1.7 light years of the star Gliese 445. By then it will be silent, but the golden record should still be readable. The journey has barely begun: even now it has covered less than a tenth of one percent of the distance to the nearest star.

// The Cargo

The Golden Record

// The Twin

And Voyager 2?

// Go Deeper

Follow the mission live

// Think It Through

Space puzzles to try

// Keep Exploring

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