How far away from Earth do we have to go until we are no longer able see it with our own eyes?
To answer this question, you have to take into account how brightly Earth reflects sunlight. And the sun itself is another important factor. As seen from any great distance, Earth appears right next to the sun – and the glare of our local star makes Earth difficult or impossible to see.
So imagine blasting off and being about 300 kilometers – about 200 miles – above Earth’s surface. That’s the height at which the space shuttle orbits. The surface of the Earth looms large in the window. You can clearly see major landforms and the lights of cities. As you pass the moon, about 380,000 kilometers – or a quarter-million miles – away, Earth looks like a bright ball in space – not very different from the way the moon looks to us. Speeding outward, you pass the orbits of Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. From all of these worlds, Earth looks like a star and gets fainter as you get farther away. The light from Earth finally becomes too faint to see with the eye alone at around 14 billion kilometers – about 9 billion miles – from home, around the outer limit of our solar system. That’s nowhere near as far as even the next-nearest star.
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