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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Index correction, was: Got your book, Bruce Stark
From: Trevor Kenchington
Date: 2004 Nov 19, 12:50 -0400
From: Trevor Kenchington
Date: 2004 Nov 19, 12:50 -0400
Alex asked:
> Does our "day vision" have higher resolution than
> the "night vision"?
Yes.
The fovea in our retinas, located in the centre of the field of view,
has the highest density of light receptors but they are primarily cones,
which are sensitive to colour but have poor low-light sensitivity. To
detect dim light, we must use the rods (not sensitive to colour but much
more sensitive to low light levels) which are either thinly scattered or
actually absent from the fovea (not sure which).
Our ability to detect low levels of light is better if the source is
viewed off-centre, since the outer parts of our retinas have more rods
(though still not to match the density of cones in the fovea). Whether
or not it would be possible to use a sextant while looking out of the
corner of your eye, I cannot say.
Trevor Kenchington
--
Trevor J. Kenchington PhD Gadus@iStar.ca
Gadus Associates, Office(902) 889-9250
R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251
Nova Scotia B0J 2L0, CANADA Home (902) 889-3555
Science Serving the Fisheries
http://home.istar.ca/~gadus
