What is a light-day? The milestone Voyager 1 is closing in on

The Voyager 1 spacecraft, traveling for nearly 50 years, volition shortly cross a mile marker reached by no another human-made entity — one light-day distant from Earth. That’s the extend a speck of ray can journey in 24 hours, equaling concerning 16 milliard miles (about 26 milliard kilometers), a item that Voyager 1 volition attain on Wednesday, Nov. 18, 2026, at 5:16:07 a.m. EST.

Its twin spacecraft, Voyager 2, took a distinct way through the sun-related scheme following they launched in 1977, in command to sojourn Uranus and Neptune. Voyager 2 is on gait to be one light-day distant from Earth in nine additional years, in November 2035.

Why measure alongside light?

Nothing in the cosmos travels faster than light. Moving through area concerning 186,000 miles all second, it crosses enormous distances in a stated period period, whether it’s a second, a day, or a year. This is true for any category of electromagnetic radiation, including apparent light, microwaves, broadcast waves, gamma rays, X-rays, or infrared. A light-day is the extend that ray volition journey in 24 hours, or 16,094,799,096 miles (25,902,068,356 kilometers). 

To put this mileage into perspective, regard several another light-distances: 

• The Moon is 238,855 miles (384,400 kilometers) from Earth, on average. The astronauts on the Artemis II goal took concerning three days to get there, but ray can traverse that extend in 1.3 seconds.
• Sunlight takes concerning eight minutes and 20 seconds to journey the 93 myriad miles from the Sun to Earth (about 150 myriad kilometers), definition our nearest celebrity is concerning 8.3 light-minutes away. 
• The extend between Earth and Mars changes as they orbit the Sun, and it can obtain anyplace from three minutes to 22 minutes for ray to journey between the two planets. Same for a broadcast transmission, either to or from a spacecraft at Mars. 
• Neptune, the most distant earth in our sun-related system, alongside an average extend from Earth of concerning 2.8 milliard miles (4.5 milliard kilometers), is four light-hours and 10 light-minutes away. It took Voyager 2, traveling concerning 35,000 miles per hour, 12 years to attain Neptune.

That’s why light-year — how far ray can journey in a twelvemonth — is used to measure and communicate the vastness of space. It’s concerning 5.88 trillion miles (9.46 trillion kilometers). The closest neighboring sun-related scheme to our own, the celebrity Proxima Centauri and its one or additional planets, is concerning 4.24 light-years distant (or, concerning 24.95 trillion miles, or 40.15 trillion kilometers). And the next-closest cosmos to our own Milky Way, the Andromeda galaxy, is concerning 2.5 myriad light-years away.

Where is Voyager 1 going?

Voyager 1 is headed in the direction of a celebrity additional than 17 light-years distant from Earth called AC +79 3888, additionally known as Gliese 445. It’s an obscure celebrity now in the constellation Ursa Minor (the Little Bear or Little Dipper), and Voyager 1 is expected to continue inside concerning 1.7 light-years of it — in 40,000 years. Even although the spacecraft, in escape since 1977, is cruising at nearly 38,000 mph (61,000 kph) through the vacuum of space, that’s a related crawl compared to the speed of light.

When Voyager 1 makes its grade Nov. 18, the spacecraft volition have taken 49 years, two months, and 11 days to have traveled one light-day beyond Earth — a huge milestone by any measure, and a day value celebrating.

See anywhere Voyager 1 is now

Use NASA’s “Eyes on the Solar System” interactive visualization tool