What is a light-day? The milestone Voyager 1 is closing in on
Voyager 1, launched in 1977, is now nearing a distance of one light‑day from Earth, meaning its radio signals take 24 hours to travel back. A light‑day equals the distance light covers in a day, roughly 26 billion kilometres. The probe’s power source is dwindling, and scientists anticipate it will cease communications within the next few years.