Purkinje effect.

Andy


----- Original Message -----
Sent: Monday, April 18, 2005 1:22 AM
Subject: Re: "sky" filter and star color


>> At 2005-04-17 07:59 -0500, Keith wrote:
>>
>> >Some of you more experienced ones may have noticed or know
>> >this, but I just recently was amazed at how well the colors
>> >of the stars show up when looking at them in the early
>> >evening around sunset while the sky is still blue.
>>
>> The color vision change is built into your eyes' rods and cones.
>> Rods are for night vision and evolution said that humans didn't need
>> color vision at night, but they do need sensitivity then.
>> Cones, less sensitive, do
>> provide color vision when the brightness is sufficient. Also, this
>> explains why averted vision is required for looking at dim nebulas -
>> no rods in the fovea.
>
> But the stars aren't brighter at dusk than they are after dark, so that
> still doesn't explain this.
> Keith mentioned that "The reddish stars in particular stand out as very
> reddish" when the sky is still blue, so I think it's very likely a
> contrast effect.
>
> -John
>
>
>
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