NASA‘s Voyager 1 will push so far from home next week that light, the fastest thing in the universe, will need a full day to reach it.
That span stretches about 16.1 billion miles in space. Set out on foot at a brisk 3 mph, and you’d need roughly 612,000 years to walk it. If you were to try to finish that course today, for example, you’d have had to start during the Middle Pleistocene, a stretch of the Ice Age more than half a million years ago.
But numbers that big tend to whizz right past the brain. So let’s try to wrestle this one down.
Since launching in 1977, Voyager 1 has buzzed past Jupiter and Saturn, snapped the famous “Pale Blue Dot” portrait of Earth and, in 2012, slipped into interstellar space, the empty stretch between the stars. At 5:16 a.m. ET Wednesday, Nov. 18, the robotic probe will add another record by reaching one light-day from Earth, or 16,094,799,096 miles. No human-made object has ever gone that far. Light makes the trip in 24 hours. Voyager 1, cruising at nearly 38,000 mph, took more than 49 years.
First, a quick speed check: Light zips through space at about 186,000 miles every second. All electromagnetic radiation moves at that speed. That’s the family of energy waves that includes visible light, radio waves, microwaves, X-rays, gamma rays, and infrared.
At that pace, sunlight takes about 8 minutes and 20 seconds to cover the 93 million miles to Earth, so that means the sun sits about 8.3 light-minutes away.
Hit the road (for a very long time)
Think a plane would help? A jet cruising at 550 mph would need about 3,340 years and a bottomless tank of fuel to fly one light-day. A flight landing today would have taken off around 1315 B.C., when King Tutankhamun ruled ancient Egypt.
Mashable Light Speed
Driving would obviously stretch the trip. If you had infinite highway laying in front of you, and you set your cruise control at 65 mph, your ride would last about 28,250 years — and that’s not accounting for pit stops and fillups. You’d have started your engine during the last ice age.
A sniper’s bullet wouldn’t make the journey short. If one left the muzzle at about 2,237 mph, it would need 821 years to cross one light-day. A bullet arriving today would have been shot around 1205, near the founding of the Mongol Empire.
Going the cosmic distance
Start close to home. Earth’s equator runs 24,901 miles around the globe, so a single light-day could circle the planet about 646,340 times to match the distance.
Now aim farther out. Pluto orbits an average of about 3.67 billion miles from the sun, so sunlight needs roughly 5.5 hours to reach it. A light-day keeps going more than four times farther than everyone’s favorite dwarf planet.
NASA’s Voyager 1 spacecraft, is headed toward the star AC +79 3888, aka Gliese 445.
Credit: Caltech / Palomar
Then try holding a conversation across that gap. Radio signals travel at the speed of light, so a long distance means a long wait. Picture a transmitter parked one light-day from Earth. Send it a message at 9 a.m. Monday, and it won’t arrive until 9 a.m. Tuesday. Its reply lands back on Earth at 9 a.m. Wednesday. Every back-and-forth takes two full days. Starting Nov. 18, Voyager 1’s team will deal with that same lag — although the spacecraft never stays still. Send a message, and while it’s traveling, the target will continue bolting farther away.
Still just a baby step
For all that, a light-day barely registers in the space between stars. Astronomers use the light-year, how far light travels in a year, to measure those gaps. One light-year is about 5.88 trillion miles.
Proxima Centauri, the closest star beyond the sun, sits about 4.24 light-years away, or about 24.95 trillion miles. That’s roughly 1,550 light-days, meaning one light-day covers less than 0.07% of the trip. Andromeda, the closest big galaxy to our Milky Way, lies about 2.5 million light-years out.
Where Voyager goes next
Voyager 1 is heading toward a dim star called Gliese 445, also known as AC +79 3888. It sits more than 17 light-years away in the constellation Ursa Minor, which includes the Little Dipper. Even at nearly 38,000 mph, Voyager 1 will need about 40,000 years to pass within about 1.7 light-years of it.
Its twin, Voyager 2, launched the same year but took a different route to visit Uranus and Neptune. Mission leaders say it’ll reach its own light-day milestone in November 2035.
Want more science and tech news delivered straight to your inbox? Sign up for Mashable’s Top Stories newsletter today.
