# The angle of the eye

**The angle of the eye** is the angular space seen by the eye with a fixed view and a fixed head. The average person has a field of view: 55^{0} up, 60^{0} down, 90^{0} outward and 60^{0} - inside . This is true only for achromatic vision (this is due to the fact that on the edges of the retina there are no receptors of cones that can distinguish color). The smallest eye angle is green, the largest is blue.

The eye angle of the animals is different. A person sees with two eyes 190^{0} in front of him. In some birds, the angle of view reaches almost 360^{0}.

The angle of the eye in one degree can be visually demonstrated by an example, calculating how far a person of medium height (1,7 meters) should go to appear at such an angle. In the language of geometry, you need to calculate the radius of a circle whose arc in 1^{0} has a length of 1,7 meters (strictly speaking, not an arc, but a chord - but for small central angles, the difference between the length of the arc and the chord is negligible).

If the arc in 1^{0} is 1,7 meters, then the total circle containing 360^{0} will have a length of 1,7x360 = 612 meters; the radius is 6 2/7 times smaller, i.e. is approximately equal to:

So, in our example, the eye angle in 1^{0} will be when the person is about 100 meters away from us. If he goes away twice as far - at 200 meters, then the angle of the eye becomes 1/2^{0}; if you approach a distance of 50 m, the angle of view of the eye will increase to 2^{0}, and so on.

After this example, it is not difficult to calculate that the angle of view of an eye for a stick of 1 meter in length will be 1^{0} when it is at a distance of 360: 44/7 = 57 from a small meter. At the same angle we see 1 centimeter from a distance of 57 centimeters, 1 kilometer from a distance of 57 kilometers, etc. - in general, any object from a distance, 57 times larger than its diameter. If you store this number - 57, then you can quickly and easily perform all calculations relating to the angular magnitude of the object. For example, if you need to determine how far you need to push the apple 9 centimeters across, so that the angle of the eye is 1^{0}, then simply multiply 9x57 - get 513 cm, or about 5 meters; from a double distance, it is seen at a half-angle of 1/2^{0}, i.e. it seems like the size of the moon.