A friend sent this email today:
Voyager 1 is about to reach one Light-day from Earth After nearly 50 years in space, NASA’s Voyager 1 is about to hit a historic milestone. By November 15, 2026, it will be 16.1 billion miles (25.9 billion km) away, meaning a radio signal will take a full 24 hours—a full light-day—to reach it.
![]() |
| An artist's rendition, obviously |
And so I looked it up, having misread the 2026 as 2025, thinking this amazing event would be celebrated far and wide! Well, no, not yet. So I did a little research (starting with an informative article from, all places, USA Today) and thought I'd share some of it here. Some factoids, a few diagrams, even a video or two. More than you ever wanted to know! But I found it fascinating. Human ingenuity at its best.
Voyager 1 was launched on September 5, 1977. It is traveling 10.6 miles a second. (Light, meanwhile, travels 186,282 miles a second.)
Curiously, Voyager 2 was launched earlier, on August 20, 1977. This was because it had a longer (more distant) mission and different trajectory than V1. It is also traveling a little slower, at 9.6 miles a second. (It is presently only 19.5 light-hours away from Earth, and I find no estimate of when it might reach a light-day away.)
Both missions included exploring Jupiter (1979) and Saturn (1980 for V1, and 1981 for V2), but V2 then continued on to fly by Uranus (1986) and Neptune (1989).
Here's a NASA video titled "A Once-in-176-Year Chance! Why Voyager Launched in 1977":
Voyager 1 left the solar system on August 25, 2012 (meaning it crossed the heliopause, the band where the solar wind's pressure is balanced by the pressure of the interstellar medium). Since entering interstellar space, the craft has been studying plasma waves, cosmic rays, and magnetic fields in the heliosphere.
Voyager 2 cross the heliopause in 2018. Only two other probes have or are on the way to accomplishing this feat: Pioneer 10 and 11. Launched in 1972 and '73, they crossed Neptune's orbit in 1983 and 1990, respectively. In the meantime, however, both have ceased to transmit (2003 in the case of 10, still earlier for 11), so their present location is unknown (though I bet a science wonk could calculate a pretty good estimate). Meanwhile, New Horizons (launched in 2006) is presently in the Kuiper Belt (home most famously of poor demoted Pluto), which it will exit in 2028 or 2029—and then on to the heliopause! But for now and ever, Voyage 1 is winning the race.
And what is the big gray band, well beyond the heliosphere? Why, it's the Oort Cloud, of course—a theoretical donut-shaped band composed of trillions of icy objects—including water, ethane, and methane ices—left over from the formation of the solar system). Which Voyager 1 won't reach for another 300 years, and it won't leave it—assuming it survives all that ice—for 3,000.
So we're quite happy with this little new milestone of a light-day! Only one earth-year to wait!




























.jpg)



























