What is the Earth's radius?

In the solar system there are nine, or, taking into account the newest arrangements in the academic environment, eight planets (Pluto lost this honorary title in 2006). Among them, the third planet, Earth, deserves special attention. Its most important feature, known to every schoolboy, is the ability to maintain a simple and highly organized life. The estimated age of the planet is over 4 billion years, which is consistent with the theory of the formation of planets from the gas cloud surrounding the Sun.

There are a number of important characteristics that every person should know, who decided to replenish his knowledge of the native planet. In this paper we will highlight precisely these characteristics.

Since the beginning of astronomical observations of the objects of the solar system and the recognition by the society of the heliocentric model of the world, the question of measuring distances in outer space was very acute. The usual "earthly" measures (meters, miles) for this task are completely not suitable. It is worth noting that although the distance from the Earth to the Moon was known already in the 17th century, it seemed insufficient for adoption as a unit. At the same time, since the Sun is always at the center of the system, and the observers - at the same distance from it (of course, it means observation from the surface of the planet), a logical decision was made-to take as the unit of cosmic distances the radius of the Earth's orbit. Further everything is simple: the orbit of the planet is close to the ideal circular, so the measurement error is minimal. At present, the distance from the Earth to the Sun is 149.59 million km and is called the "astronomical unit" (au). Every year, because of the decrease in the solar mass, its increase by 15 cm is fixed. Based on the foregoing, it is possible to calculate the distance from Pluto to the Sun - 39.4 AU etc.

What is the radius of the Earth, everyone knows. The statement "The Earth has the shape of a ball" is now a symbol of time, contrasted with ancient beliefs about a flat form. Thus, the average radius is 6,371 km. However, this value is not entirely true. As is known, due to the tilt of the earth's axis, a lot of snow and ice are constantly present on the poles (the so-called "polar caps"). Because of them, the planet's mass is redistributed, and the Earth's radius, measured at the poles, differs from its value along the equator. The error is relatively small, but it is. For example, the equatorial radius of the Earth is 6378.1 km, while the polar radius is 6,356.8 km. And recently there have been changes in the poles caused by climatic anomalies. From all the above it follows that when answering the question "What is the radius of the Earth?", It is necessary to clarify which measurement is implied. Only in this case it is possible to give an exact answer.

Few people know that the presence of our planet's natural satellite - the moon - could indirectly affect the radius of the Earth. According to one of the hypotheses, at the early stage of the existence of the solar system, the Earth shared its orbit with another large planetoid of the size of Mars and a mass equal to 10% of the terrestrial one. Once this hypothetical planet (Theya) collided with the Earth. As a result, some of its mass was ejected into a near-earth orbit, forming the Moon, and the remainder became part of the Earth, by increasing the radius with such an "additive." Other prominent scientists claim that the collision occurred along a tangential trajectory, so Tei was not destroyed. In this case, the Moon is part of our planet, thrown into a circular orbit. In turn, the radius, for obvious reasons, did not increase, but decreased.

As you can see, sometimes, it would seem, simple questions can not be answered directly. As Pascal said, "The object of knowledge is infinite."