just want a sensible answer to this question does anyone actually know is there a limit and if so how far is it
2006-10-20 11:07:48 · 15 answers · asked by johncraig74@btinternet.com 1 in Science & Mathematics ➔ Biology
Many millions of miles. The eye sees because it is sensitive to light so if there is sufficient light arriving were it is it will see. Some light comes from stars and other galaxies that are millions of miles away. Because they are so far only a very small amount of the light arrives but enough to see
2006-10-20 11:12:37 · answer #1 · answered by Maid Angela 7 · 1⤊ 0⤋
The limit actually depends on a lot of things. If we assume someone has 20/20 vision and the person is in the darkness of space then the only limiting factors are the brightness of the object, the distance, the wavelength of light it emmits, and the human eye itself.
The eye uses rods to detect light. A rod will actually register a single photon but your brain will ignore it. For your brain to detect the light, a bundle of 7-9 photons must strike the rod and 500-900 must arrive at the surface of your eye.
Using this information, along with the luminosity of the brightest object in the observable universe (which isn't visible to the naked eye) one could calculate the distance at which this object would just be visible to some people.....which I'm not going to do.
I will say, however, all conditions being ideal, one might be able to see M81, a 5.7 magnitude galaxy 12 million light years away.
2006-10-21 03:44:02 · answer #2 · answered by minuteblue 6 · 0⤊ 0⤋
There is no actual limit. At very great distances the light source must be very large or very intense to be visible.
The most distance object visible with the unaided eye is probably the Andromeda galaxy (M31) at about 2.2 million light years.
While it's apparent size is larger than the full moon, it is so dim that there is no documented observations of it before ~600AD.
It has to be a perfectly clear and dark night with the galaxy nearly overhead. Then after looking for a while you may detect the hazy spot in the sky. Use a star chart to know where to look.
If there is a moon in the sky or any artificial lighting visible it will be impossible to find the Andromeda galaxy without a telescope or binoculars.
2006-10-20 18:39:23 · answer #3 · answered by bee 3 · 0⤊ 0⤋
The relevant variable is not distance, it is brightness and angular size at the eye. The limiting brightness is what astronomers call '6th magnitude' and the angular size is what corresponds to one 'pixel' for our vision: the size of a rod or cone cell in the eye.
With that said, the farthest thing that a human can see without a telescope is the Andromeda Spiral galaxy, which is about 2 million lightyears away. If there were a further galaxy that was bright enough, we would be able to see that also,but there isn't.
2006-10-20 18:34:49 · answer #4 · answered by mathematician 7 · 2⤊ 0⤋
You see because the light reaches your retina. You can see
as far as a light source can reach your retina with enough instensity.
Theoretically that would mean human's sight is infinite but on the other hand, there isn't such thing as a straight line.
In the immensity of the universe you cannot draw a straight line ... without "hitting" something.
So the humam eye can see until its linesight "hits" an obstacle.
2006-10-20 18:59:23 · answer #5 · answered by rebel_g 2 · 0⤊ 0⤋
no limit in distance.
the limit is just one of sensitivity.
have you ever noticed the stars in the night sky?
have you ever looked at the constellation, Cygnus?
well, Deneb (alpha Cygni) is 3'200 light years away from us.
(as a reminder, a light year is not far from 6'000 billion miles. So Deneb is 1.9E16 miles away from us)
this is by no means the most distant object we can see (it is one of the brightest stars in our night sky), but it gives you a first hint of an idea.
2006-10-20 19:26:44 · answer #6 · answered by AntoineBachmann 5 · 0⤊ 0⤋
Triangulum galaxy M33, 3 million light years is generally considered the furthest object visible to the naked eye of most people.
2006-10-20 18:37:51 · answer #7 · answered by Anonymous · 0⤊ 0⤋
There are high mesas from which you can see things 100 miles away. Mesa Verde is one of them, in Colorado near where four corners come together.
2006-10-20 18:22:01 · answer #8 · answered by Anonymous · 0⤊ 0⤋
there's no limit: light travels into the eye and thats how we see: providing there's light we can see it: even if it were thousands of miles away: if its big enough you could see anything
2006-10-20 21:44:56 · answer #9 · answered by Ollie 5 · 0⤊ 0⤋
On a clear day you can see forever.
2006-10-20 18:50:28 · answer #10 · answered by Anonymous · 1⤊ 0⤋