Think back to the late summer of 1977. Maybe you were packing the car for one last trip before school started. Maybe you were flipping through albums at the record store.
That year, NASA sent a spacecraft called Voyager 1 on its way. It has not stopped since.
On Wednesday, November 18, it will reach a mark no human-made object has ever touched. It will be one full light-day from Earth.
What Is a Light-Day, Anyway?
A light-day measures distance, even though it sounds like time. It is how far light travels in 24 hours.
That works out to 16.094 billion miles. The moment has been worked out to the second: 5:16:07 a.m. Eastern time.
Picture what that means for the people who still look after the spacecraft. A signal moving at the speed of light will need a full day to get there. The reply will need another day to come home.
Ask a question on Monday morning. Hear the answer on Wednesday morning.
No other machine built by people has gone this far.
The Long Way Out
Voyager 1 did not set out alone. It had a twin, Voyager 2, launched the same year, and the timing was no accident.
The four largest planets (Jupiter, Saturn, Uranus, and Neptune) had lined up in a way that happens once every 175 years. The gravity of each planet could send a spacecraft on toward the next one. Think of a stone skipping across a pond, with planets for water.
Voyager 1 flew past Jupiter and Saturn, then headed for the edge of the solar system. On the way out, it took one more portrait of the solar system, including a last image of a pale blue dot. That dot was Earth. Its cameras have been off since February 1990, shut down to save power.
In August 2012, it crossed the boundary where the wind from the Sun gives way to the space between the stars. Only two spacecraft have ever operated out there. The other is its twin.
Most of its instruments have been shut down over the years, mainly to save power. Two are still on. And the spacecraft is still in touch with home.
The Record on Board
Here is the part that may make you smile. Each Voyager carries a 12-inch phonograph record.
A real one. It is plated in copper and gold, and it is called the Golden Record. It holds spoken greetings in 55 languages, 27 pieces of music, 116 images, and other sounds from Earth.
The cover is etched with instructions on how to play it. You already know how. Anyone else who comes across it will have the diagram.
One line travels with it: “Hello from the children of planet Earth.”
That record has been riding along for 49 years. Think of what has come and gone in our living rooms since then: eight-tracks, cassettes, compact discs. The record is still going.
Where to Look
Voyager 2 took a longer route past all four big planets, so it trails its twin. EarthSky reports that it is not expected to reach its own light-day until November 2035.
As for Voyager 1, there is nothing to see with your own eyes. There is a direction, though. It is traveling toward the constellation Ophiuchus, the Serpent Bearer.
If you would like to face it, look toward the western horizon around 5 p.m. on November 17, the evening before the milestone.
Something we built in 1977 is still out there, and it still answers when we call. Soon, it will just take a day.
