If a person is standing on a road that goes on for hundreds for miles and a car starts coming down the road how many miles away would the car have to be before the person could see the car?
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About 7 because of the curve of the earth.
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According to Wikipedia the formula for the distance to the horizon is
D{miles} = 1.22*√(h{feet}) where units are in { } brackets and h is the height of the observer's eyes
The height of the car would have a negligible effect on this.
given h = 5'7", D ~ 2.9 miles
In optimal lighting conditions, the 'perfect' human eye can resolve objects with (white/black) maximum contrast if they are 0.4 minutes of arc apart. (THe normal human eye will be less than half this good and will be able to resolve objects about a minute of arc apart - in perfect viewing and lighting conditions.) That equates to a 6 foot object at 9.77 miles.
Obviously if sunlight is reflected off of the object, the distance can be measured in thousands of miles.
We are able to see starlight from about 30,000 light years away as a distinct point.
D{miles} = 1.22*√(h{feet}) where units are in { } brackets and h is the height of the observer's eyes
The height of the car would have a negligible effect on this.
given h = 5'7", D ~ 2.9 miles
In optimal lighting conditions, the 'perfect' human eye can resolve objects with (white/black) maximum contrast if they are 0.4 minutes of arc apart. (THe normal human eye will be less than half this good and will be able to resolve objects about a minute of arc apart - in perfect viewing and lighting conditions.) That equates to a 6 foot object at 9.77 miles.
Obviously if sunlight is reflected off of the object, the distance can be measured in thousands of miles.
We are able to see starlight from about 30,000 light years away as a distinct point.
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It depends on how clear is the sky and how tall is the car and the observer.
For an observer standing on the ground with h = 1.70 metres (5 ft 7 in) (average eye-level height), the horizon is at a distance of 5.0 kilometres (3.1 mi).
So then for a car that is about the same height as the observer, roof at 5'7" then the observer can just barely see the roof of the car over the horizon at 6 miles distance.
Of course it helps to climb a handy rock, tree or stepladder.
For an observer standing on the ground with h = 1.70 metres (5 ft 7 in) (average eye-level height), the horizon is at a distance of 5.0 kilometres (3.1 mi).
So then for a car that is about the same height as the observer, roof at 5'7" then the observer can just barely see the roof of the car over the horizon at 6 miles distance.
Of course it helps to climb a handy rock, tree or stepladder.
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It depends on the persons vision.
*** g99 5/8 pp. 5-6 Your Brain—How Does It Work? ***
The millions of neurons of the optic nerve arrive at a junction in the brain known as the optic chiasma. Here neurons carrying signals from the left-hand part of each eye’s retina now meet and follow parallel tracks to the left-hand side of the brain. Similarly, signals from the right-hand side of each retina join forces and travel to the right-hand side. The impulses arrive next at a relay station in the thalamus, and from there the next neurons pass the signals to the area at the back of the brain known as the visual cortex.
*** g99 5/8 pp. 5-6 Your Brain—How Does It Work? ***
The millions of neurons of the optic nerve arrive at a junction in the brain known as the optic chiasma. Here neurons carrying signals from the left-hand part of each eye’s retina now meet and follow parallel tracks to the left-hand side of the brain. Similarly, signals from the right-hand side of each retina join forces and travel to the right-hand side. The impulses arrive next at a relay station in the thalamus, and from there the next neurons pass the signals to the area at the back of the brain known as the visual cortex.
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