# How much sky do we see at any one moment?

When we look at any particular point the sky, what percentage of the celestial sphere do we see?

This question arises from the notion that on average there passes one meteor per hour overhead. So assuming that one were to stare in one direction for one hour and during that hour exactly one meteor appears, what are the changes of the viewer having seen it?

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What is the source of that notion on average there passes one meteor per hour overhead the word overhead seems ambiguous. This is a tough question...human field of view? – TryTryAgain Jan 6 '12 at 0:47
Half of the celestial sphere is visible at any given time, minus mountain ranges, trees, buildings, etc. – Andrew Jan 6 '12 at 1:39
@Andrew: Yes, but the question is about a human observer's field of view, which is less than a full hemisphere. – Keith Thompson Jan 6 '12 at 2:07
@TryTryAgain: I have actually heard that from several places. This source lists the frequency as "few per hour on an average night". – dotancohen Jan 6 '12 at 8:59
There is also a variable involved here. If you look to the direction of some constellation say Draco and it is happened to be the time of Draconids then you will see much more than "on average". – Tigran Khanzadyan Jan 6 '12 at 11:15

Different animals have different fields of view, depending on the placement of the eyes. Humans have an almost 180-degree forward-facing horizontal field of view, while some birds have a complete or nearly-complete 360-degree field of view. In addition, the vertical range of the field of view in humans is typically around 100 degrees.

The range of visual abilities is not uniform across a field of view, and varies from animal to animal. For example, binocular vision, which is important for depth perception, only covers 120 degrees (horizontally) of the field of vision in humans[citation needed]; the remaining peripheral 60 degrees have no binocular vision (because of the lack of overlap in the images from either eye for those parts of the field of view). Some birds have a scant 10 or 20 degrees of binocular vision.

Similarly, color vision and the ability to perceive shape and motion vary across the field of view; in humans the former is concentrated in the center of the visual field, while the latter tends to be much stronger in the periphery. This is due to the much higher concentration of color-sensitive cone cells in the fovea, the central region of the retina, in comparison to the higher concentration of motion-sensitive rod cells in the periphery. Since cone cells require considerably brighter light sources to be activated, the result of this distribution is that peripheral vision is much stronger at night relative to binocular vision.

So a human observer should be able to see roughly half of the visible sky, or a quarter of a full sphere. If you look about 50° above the horizon, you should be able to see an area of the sky extending from directly to your left to directly to your right horizontally, and from the horizon to about 10° past the zenith.

You won't be able to see as well around the edges of your field of view. Depth perception isn't relevant when looking at the sky, but being able to see with both eyes is probably better than seeing with just one.

This can vary from person to person; some people have much better peripheral vision than others.

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Thanks, Keith. The angle of the field of view only pertains to left-right, but not to up-down. I could find no reference to the average human's field of view in the up-down axis. – dotancohen Jan 6 '12 at 8:46
@dotancohen: Are you referring to what you were able to find before I posted my question? The first paragraph I quoted says the vertical field of view is about 100 degrees. – Keith Thompson Jan 7 '12 at 0:03
Somehow I read right over that line. Thank you, it does complete the answer then! – dotancohen Jan 7 '12 at 0:21