Stars twinkle because of the atmosphere’s slightly fluctuating refractive properties (compare to mirages). I’m sure you can notice dim stars disappearing when you look straight at them, but I’m going to keep the atmosphere story for now—even though the only way I’ve tested it is to compare with planets (whose images are disclike rather than pointlike).
I take it you haven’t spent much time star gazing?
The “foveal blind spot” is how the fovea has a very high density of cones, which gives great acuity with color vision, but unfortunately almost no rods, so very poor performance under low-light conditions.
To view faint stars, you look slightly off to the side while still concentrating on the object. This is called averted vision.
I’ve stargazed, though now only when I go camping (boo Los Angeles). You’re right—I’d forgotten about the experience of averted vision.
It’s funny that I said “with one eye”—I was assuming that the (optic nerve) blind spot was off-center in each eye. Obviously parallax hardly applies to stars, so relative night blindness to stars in the center few degrees of your vision wouldn’t depend on having only one eye open.
The optic nerve blind spot is off-center, toward the side away from your nose in your field of vision, and it’s a total blind spot. The fovea is in the center of your field of vision and isn’t really a blind spot, it’s just specialized for higher resolution at the expense of sensitivity so it becomes like a second blind spot in dim conditions.
Stars twinkle because of the atmosphere’s slightly fluctuating refractive properties (compare to mirages). I’m sure you can notice dim stars disappearing when you look straight at them, but I’m going to keep the atmosphere story for now—even though the only way I’ve tested it is to compare with planets (whose images are disclike rather than pointlike).
See any number of google hits on “why stars twinkle” e.g. http://astroprofspage.com/archives/1168
I take it you haven’t spent much time star gazing?
The “foveal blind spot” is how the fovea has a very high density of cones, which gives great acuity with color vision, but unfortunately almost no rods, so very poor performance under low-light conditions.
To view faint stars, you look slightly off to the side while still concentrating on the object. This is called averted vision.
I’ve stargazed, though now only when I go camping (boo Los Angeles). You’re right—I’d forgotten about the experience of averted vision.
It’s funny that I said “with one eye”—I was assuming that the (optic nerve) blind spot was off-center in each eye. Obviously parallax hardly applies to stars, so relative night blindness to stars in the center few degrees of your vision wouldn’t depend on having only one eye open.
The optic nerve blind spot is off-center, toward the side away from your nose in your field of vision, and it’s a total blind spot. The fovea is in the center of your field of vision and isn’t really a blind spot, it’s just specialized for higher resolution at the expense of sensitivity so it becomes like a second blind spot in dim conditions.
So the optic nerve blind spot wouldn’t really be noticeable when stargazing with both eyes. That’s what I was expecting or vaguely recalling.