| The horizon on Earth is the line that limits sight distance. It seems to separate the sky from the ground or the sea horizon is not located at an infinite distance on the contrary it is close enough. The circular line is variable depending on the height of observation, the observer is focused where heaven and Earth seem to join. This horizontal plane and tangential to the Earth's surface is the horizon that limits what can be observed due to its own position or situation. The horizon takes into account the curvature of the Earth. In astronomy, the cosmic horizon or cosmological horizon means the limit of the observable universe from Earth. * On this beautiful sunset distance, one can see the layers of the atmosphere. This image of the horizon of the Earth, was taken by the crew of STS-129 Space Shuttle International.
Image Credit: NASA | | 
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Where is the horizon?
For a man of 1.80 meters in the sea, the horizon is approximately 4789 meters.
How to calculate the distance to the horizon?
Next the right figure, we will use distance from Earth's radius, the mean radius is 6 371.0 km.
R = radius of Earth = 6371000 m
h = height of the observation = 1.8 m
D'= distance of the horizon
D = AR (equivalent to R tan A) = D'
D2 + R2 = (R + h)2 = R2 + 2hR +h2 equivalent 2hR
D2 = 2hR + h2 = 22 935 600
D = 4 789.11 meters
Nota: Equatorial radius of Earth = 6 378.137 km
Polar radius of Earth = 6 356.752 km
Mean radius = 6 371.0 kilometers | | | Height of the observer | | Distance of the horizon | | | | | | 1 m | | 3,569 km | | 1.80 m | | 4,789 km | | 5 m | | 7,981 km | | 10 m | | 11,288 km | | 20 m | | 15,963 km | | 50 m | | 25,240 km | | 100 m | | 35,696 km | | 500 m | | 79,820 km | | 1 km | | 112,884 km | | 5 km | | 252,457 km | | 10 km | | 357,099 km | | 20 km | | 505,212 km | | 50 km | | 799,749 km | | 100 km | | 1 133,225 km | | 200 km | | 1 608,850 km | | 500 km | | 2 573,130 km |
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