Google 'rods cones retina'.
Google 'rods cones retina'.
If you can't see it how do you know you're looking directly at it?
Because you can move your head from side to side and it disappears in the middle. That can either be because:
1) The star stopped shining x light years ago at exactly the correct time, and started shining again at exactly the correcy time:
or
2) The retina has less light sensitive cells in the centre of vision, more sensitive at the periphery.
If nobody can understand it I'll explain in the morning. Right now just pulled a cork and going to get squiffy
1) The star stopped shining x light years ago at exactly the correct time, and started shining again at exactly the correcy time:
or
2) The retina has less light sensitive cells in the centre of vision, more sensitive at the periphery.
If nobody can understand it I'll explain in the morning. Right now just pulled a cork and going to get squiffy
The bit where the brain is you mean?
I'd stop moving my head from side to side if I were you.
Don't ever go to wimbledon.
It's called averted vision, astronomers use it quite often.
I don't understand this. I do know that peripheral vision is more sensitive to movement, but why should a pinpoint of light disappear when you look directly at it?
I second that, and the reason is the optic nerve area has a black spot (the optical nerve bundle area) and so you won't see some tiny things at a long distance and when you move your eye lens slightly away you start seeing these previously not seen stars,but as soon as you re-focus directly on it and it disappears again! I do Astronomy so have to see many faint things this way using so called averted vision.
Yes, but the 'blind spot', the area where the optic nerve enters the retina, is not at the centre of vision. To make something disappear by centring its image on the blind spot, you would have to look several degrees to the side and slightly upwards.
If you look directly at something, it should not 'disappear' unless, of course, there is a problem with your vision.
I think the blind spot is a relatively minor reason for the effect, which does exist, and has a real physiological explanation. It's actually a very interesting subject as it shows that the eye has evolved from something quite primitive, which of course our resident fruitcake refuses to accept ever happened.
Basically the bit of the retina which is used when looking directly at something has lots of cones (a cell type) in that area. The cells in the part of your eye which deals with peripheral vison are mainly rods (a different cell type).
Cones are very sensitive to colour, but not sensitive to low level light. Rods are not very sensitive to colour, but very sensitive to low level light.
So if you look directly at something you are using relatively 'blind' cells so if the light is quite dim you might not pick it up, whereas if you move your eye to the side the far more sensitive rod cells 'see' the light so pick it up.
Now people have also mentioned sensitivity to movement. This is also a fascinating part of the human (mammalian) visual system. When you see a flashing light or movement in the periphery, this gets processed in a more primitive part of the brain and not immediately in the visual cortex which is a more recent development.
But the effect certainly exists, can be explained using the retinal cells involved, and also provides strong evidence that evolution exists !
Good points, Chapeau.
Yes, the cones in the centre of vision are less sensitive in low light, which is why all colour seems to disappear on a dark night. I must confess that I had never noticed that it is possible to see the dimmer stars by looking off-centre. I must try that sometime.
Yes, the cones in the centre of vision are less sensitive in low light, which is why all colour seems to disappear on a dark night. I must confess that I had never noticed that it is possible to see the dimmer stars by looking off-centre. I must try that sometime.
Sky is very clear tonight here in London, about to go up on my flat roof to do some star gazing , I will be using my averted vision to make some of the faintest galaxies, despite a 14'' Meade LX200, you still need to use averted vison, it is like you are not looking directly at the point of interest, but you are kind of pretending you are not watching it, and are looking at something else, and then you start seeing the faint object quite clear, and as soon as you bring your eye to the object you were watching from the side of your eye, it goes off the vision!
It is like you are at your office desk and watching the beautiful wife of your boss without looking directly at her, though your eyes are on the computer screen, and you are watching her beautiful large tits!
It is like you are at your office desk and watching the beautiful wife of your boss without looking directly at her, though your eyes are on the computer screen, and you are watching her beautiful large tits!
I need that stuff they put in your eyes to dilate pupils, I am sure that would double the power of my telescope effectively as more light would reach my retina.
Antropine!! It is also used in NBC warfare, if you should get a dose of nerve gas, you simply inject yourself with Antropine, if however you misdiagnosed your symptoms, then the Antropine will probably kill you...
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