[Marxism] twinkle twinkle -was America No. 1?
rholt at planeteria.net
Sun Mar 6 15:59:16 MST 2005
There's a misunderstanding here. As a fact, the image of a point source
light is just a bit larger than the light detectors in the eyeball
(given good young eyes). A slight motion of the image on the retina
causes one group of detectors to stop and an adjacent group to start.
These starts and stops are the apparent twinkle. If motion were going to
cause the whole field of view to wobble, then your vision would be
wobbling all the time. The brain compensates for field wobble provided
it has sufficient imformation (a resonable image, such as the whole
sky). Since there is no coherence between the physical distribution of
the eyeball's detectors and the pattern and/or location of the point
source lights, none will twinkle "coherently," as you put it.
Also, a black background is necessary. As anyone who has taken
photographs through a telescope will tell you, atmospheric disturbances
such as heat waves when observing a low azimuths will cause the image to
move, not twinkle.
Les Schaffer wrote:
> Rod Holt wrote:
>> The major cause of human perception of twinkle is that the image of a
>> really, really small light source is focused to such a small spot on
>> the retina--just a few rods & cones--that as the eyeball moves ever
>> so little,
> that would cause the entire field of view to wobble, not individual
> stars seperately twinkling. further the stars would maintain constant
> intensity. check out two distant streetlights in the desert near dusk.
> you think the lights twinkle coherently? same for stars?
> different timescales and amplitudes too, i would guess.
> les schaffer
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