how far can a human eye see

A healthy human eye with 20/20 vision can typically see about 3 miles (approximately 5 kilometers) on a flat surface due to the curvature of the Earth, which limits how far the ground is visible. This distance represents the horizon line for an average person's eye level about 5 to 6 feet above the ground. Beyond this, Earth's curvature causes objects at ground level to disappear from view. However, this doesn't mean the eye cannot see farther. For instance, bright and large objects such as mountains, tall buildings, the sun, moon, or stars can be seen from much greater distances, even millions of miles away in the case of stars and galaxies, because they emit or reflect enough light to be visible to the naked eye from far away. From elevated vantage points like skyscrapers, planes, or mountains, a person can see objects hundreds of miles away. Ultimately, the limit for the human eye seeing ground-level objects is generally about 3 miles due to Earth's curvature, but the range is technically infinite for bright, large, or high-up objects. Other factors influencing sight distance include eye health, brightness of the object, size, obstructions in the line of sight, and atmospheric conditions.