You see because the light reaches your retina. You can see as far as a light source can reach your retina with enough intensity How far the human eye can see depends on how many particles of light, or photons, a distant object emits. Theoretically, there is no limit to the distance we can see, the object just has to be large enough or emitting enough radiation. So the human eye can see until its line-sight hits an obstacle. Healthy human sight can see an almost unlimited distance. Normally vision is stopped by something blocking it. If you are looking at the horizon the curve of the earth stops you from seeing farther. The farthest thing that a human can see without a telescope is the Andromeda Spiral galaxy, which is about 2 million lightyears away.
Wednesday, May 22, 2013
How far can the human eye see?
You see because the light reaches your retina. You can see as far as a light source can reach your retina with enough intensity How far the human eye can see depends on how many particles of light, or photons, a distant object emits. Theoretically, there is no limit to the distance we can see, the object just has to be large enough or emitting enough radiation. So the human eye can see until its line-sight hits an obstacle. Healthy human sight can see an almost unlimited distance. Normally vision is stopped by something blocking it. If you are looking at the horizon the curve of the earth stops you from seeing farther. The farthest thing that a human can see without a telescope is the Andromeda Spiral galaxy, which is about 2 million lightyears away.