The human eye can typically see about 3 miles (approximately 5 kilometers) on a flat surface before the Earth's curvature limits the view. This distance is for a person with normal vision standing with eyes around 5 feet (1.5 meters) above the ground. From higher elevations, the visible distance extends significantly; for example, from very tall buildings or mountains, visibility can reach tens or even hundreds of miles. Additionally, when looking at the sky at night, humans can see stars and galaxies millions of light-years away because there is no horizon restricting the view in space.

Factors Affecting How Far We Can See

• Earth’s curvature: It limits the line of sight from ground level to about 3 miles.
• Elevation: The higher the observer's eye level, the farther they can see—for example, from the Burj Khalifa’s observation deck, visibility can extend up to 60 miles.
• Object size and brightness: Large and bright objects can be seen from much farther away than smaller or dimmer ones.
• Atmospheric conditions: Clear weather significantly enhances visibility, while fog, pollution, or haze reduces the distance one can see.
• Visual acuity: People with better than average eyesight can distinguish smaller objects at greater distances.

Thus, the distance visible to the human eye is not a fixed limit but varies with physical, environmental, and physiological factors.