Voyager 1 will cross one light-day from Earth at 5:16 a.m. ET on November 18, meaning a radio message sent to it would take a full 24 hours to arrive.
A light-day is the distance light travels in a day, roughly 16 billion miles in this case. Radio signals move at light speed, so a command and its acknowledgment now make a two-day round trip. The probe keeps moving at nearly 38,000 mph, so that lag will only grow. Voyager 1 launched in 1977, timed to a planetary lineup that recurs every 176 years, and left the heliosphere (the bubble of solar wind around the sun) in 2012.
NASA has planned two events. After sunset on November 17, it is asking people to point a light at the sky and flash VGR, Voyager's call sign, in Morse code. NASA built an online flasher for phones and tablets. By hand, dots should last under a second and dashes about one second. The gesture is symbolic: the beam would spread across billions of miles, and virtually every photon would miss a spacecraft about 12 feet across.
The celebration comes with a caveat. Voyager 2, which left the solar system in 2018, will not reach a light-day until November 2035, most likely after its fuel is gone. Both probes are running low on plutonium-fueled power, and since 2024 the team has shut off two science instruments on each. This year, engineers swapped three power-hungry heating devices on each probe for three lower-power replacements, a fix they nicknamed the "Big Bang" that should buy at least another year. In October, a thruster problem on Voyager 1 briefly caused a communication blackout, and the cause is still unknown.
The milestone is a distance record, but the harder story is how long anyone can keep talking to the twins at all. Mission leaders and senior NASA science officials will take that up at noon ET on November 19 at the Jet Propulsion Laboratory, streamed on NASA+ and YouTube. The briefing is scheduled to cover how the spacecraft are holding up, what they are still learning beyond the sun's bubble, and how engineers keep such old hardware running from so far away.