How far away from Earth can we be and see it still with our own eyes?
To find the answer, let’s take an imaginary trip through the solar system, to see how Earth looks from various other places, in our own neighborhood of space. Spacecraft exploring our solar system have given us marvelous views of Earth.
First, imagine blasting off and being about 200 miles (300 km) above Earth’s surface. That’s about the height of the orbit of the International Space Station (ISS). From the window of ISS, the surface of the Earth looms large. In the daytime, you can clearly see major landforms. At night, from Earth orbit, you see the lights of Earth’s cities.
Let’s get farther away, say, the distance of the orbit of the moon.
As we pass the moon – some quarter million miles (about 380,000 km) away – Earth looks like a bright ball in space. It’s not terribly different from the way the moon looks to us.
The first images of the Earth from the moon came from the Apollo mission. Apollo 8 in 1968 was the first human spaceflight to leave Earth orbit. It was the first earthly spacecraft to be captured by and escape from the gravitational field of another celestial body, in this case the moon.
It was the first voyage in which humans visited another world and returned to return to Earth.
In the decades since Voyager first began traveling outward, moon exploration has become more common. The robotic Kaguya spacecraft orbited around Earth’s moon in 2007. Launched by Japan, and officially named the Selenological and Engineering Explorer (SELENE), Kaguya studied the origin and evolution of the moon. The frame below is from Kaguya’s onboard HDTV camera.
Now let’s keep moving outward, until we can see both the Earth and moon together in space. The next picture was mind-blowing when first released. It shows a crescent-shaped Earth and moon – the first of its kind ever taken by a spacecraft – on September 18, 1977.
Since 1977, many robot spacecraft have ventured outward into our solar system. The mosaic below shows images of Earth and the moon acquired by the multispectral imager on the Near Earth Asteroid Rendezvous Spacecraft (NEAR) on January 23, 1998, 19 hours after the spacecraft swung by Earth on its way to the asteroid 433 Eros. The images of both were taken from a range of 250,000 miles (400,000 km), approximately the same as the distance between the two bodies.
Speeding outward from the Earth and moon system, you pass the orbits of the planets Mars, Jupiter and Saturn. From all of these worlds, Earth looks like a star – which gets fainter as you get farther away.
The images above are from Saturn, the sixth planet outward in orbit around the sun. I’ve never seen any image of Earth from Uranus or Neptune or any other body beyond Saturn’s orbit. Only five spacecraft from Earth – the two Voyager spacecraft, the two Pioneers, and the New Horizons spacecraft, which passed Pluto in 2015 – have ever ventured that far. Those craft weren’t designed to look back at Earth, and, to my knowledge, they didn’t capture images of Earth from distances beyond Saturn.
But, speaking theoretically now, could Earth be seen from distances beyond Saturn?
Speaking only in terms of Earth’s brightness, the answer is yes. Our world doesn’t become too faint to see with the eye alone until far beyond Neptune’s orbit, at around 9 billion miles (14 billion km) from home. Now consider Pluto’s orbit. It’s highly elliptical, stretching from just 2.7 billion miles (4.4 billion km) to over 4.5 billion miles (7.3 billion km) from the sun. Pluto is within the limiting distance at which – if we just consider brightness alone, no other factors – we should be able to see Earth with the eye alone.
But there is another factor. As you go outward from Earth, our world appears closer and closer to the blazing sun. As you get farther away, the sun’s glare begins to overwhelm the view of Earth. From Pluto – even though Earth would be bright enough to see – you probably couldn’t see it in the sun’s glare.
So that is the answer. Although no one knows for sure because no one has tried it (and because human eyesight varies from person to person), the Earth would become impossible to see with the eye somewhere beyond Saturn’s orbit.
Now let’s change the game. Let’s say we could use instruments, and not just the eye alone. Suppose intrepid astronaut-astronomers went to Pluto. Suppose they took all the instruments they needed to view Earth in the sun’s glare. Could they use telescopes, obscuring disks, and other techniques to get a glimpse of Earth? Maybe!
But it still wouldn’t be easy.
Bottom line: How far away in space could you view Earth with the eye alone? Considering only brightness, the answer is about 9 billion miles (14 billion km) away. In practice, though, seeing it from that distance would be a challenge because the sun’s glare would overwhelm the view of Earth.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.