What is a horizon? We often use this word, for example: the sun hid behind the horizon or a car appeared on the horizon. But is there a scientific definition of this term and is it possible to measure the distance to the horizon?
What is a horizon?
In simple terms, this is the boundary between heaven and the surface of the earth or water. You can also sometimes find the word "visible" in the definition. The horizon is visible and true.
The visible horizon is that part of the space that the observer sees, including the boundary between the sky and the earth's surface. The true horizon is the imaginary circle of the celestial sphere, the plane of which is perpendicular to the vertical line at the observer's point. It is also called astronomical or mathematical.
Distance is measured to the visible horizon. For this, the Pythagorean theorem and a simple formula are used:
d = √ (R + h)2 - R2
To know a more or less accurate distance, you need to know two quantities: the radius of the Earth (R) and the height at which the observer is (h). Thus, it is obvious that the higher the observer is, the stronger the horizon line will move away.
Examples of distances from a specific object to the horizon:
- a person with a height of 1.75 m, standing on the ground - 4.7 km;
- roof of an 8-storey building 25 m - 17.9 km;
- balloon 150 m - 43.8 km;
- 10 km - 357.3 km;
- spacecraft 350 km - 2144 km.
Interesting fact: The horizon on the moon looks very different.Due to the lack of atmosphere, distant objects look sharper than on Earth. Also, the difficulty in studying this phenomenon is due to the fact that there are no familiar objects by which one could estimate the scale. In general, the lunar horizon is 2 times closer.
Visibility range
If we imagine that the observer is standing on a flat surface and nothing is blocking the horizon, then what is his horizons limited by? In open space, the horizon line is limited by the convexity of the Earth's surface, associated with its geoid shape.
The previous image shows that the visibility for the observer ends at the point where the horizon line conditionally intersects with the geoid shape of the Earth. If the observer rises higher, his horizons will expand.
The question is, can different devices increase their visibility range? For example, is binoculars able to broaden their horizons in the literal sense? Since binoculars are an optical device, it can only enlarge the image. To do this, it is equipped with a special design that increases distant objects, makes them more distinct. But you cannot “peek” beyond the horizon with binoculars.
Horizon is the border dividing the sky and the surface of the earth / water. The distance to the visible horizon depends on the height at which the observer is. The higher this point, the stronger the horizon moves away. For example, from a height of average human height (1.75 m), the distance to the horizon is 4.7 km.
