When NASA's Voyager 1 launched from the Kennedy Space Center in Florida on September 5, 1977, the mission was only designed to last five years. But in 2026, the spacecraft is still flying and sending back data, and it's about to reach an incredible new milestone.

On November 18, 2026, Voyager 1 will make history when it becomes the first human-made object to reach one light-day from Earth. A light-day is the distance it takes for light to travel in 24 hours, equal to about 16.1 billion miles (25.9 billion km). To put that distance into perspective, light from the sun takes just over eight minutes to reach Earth, traveling at around 186,000 miles (300,000 km) per second. So a light-day is a colossal distance, equivalent to about 173 times the expanse between Earth and the sun.

But the milestone is about more than just distance. It also highlights the increasing communication delay between mission controllers on Earth and the Voyager 1 spacecraft as it continues to race away from its starting point.…