In the solar system, there are nine, or, given the latest agreements in the scientific community, eight planets (Pluto lost this honorary title in 2006). Among them, the third planet, the Earth, deserves special attention. Its most important feature known to every student 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 a gas cloud surrounding the sun.
There are a number of important characteristics that every person should be familiar with, who decides to replenish their luggage of knowledge about their home planet. In this paper, we will highlight 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 has been very acute. The usual “earthly” measurements (meters, miles) were completely unsuitable for this task. It is worth noting that although the distance from the Earth to the Moon was already known in the 17th century, it seemed insufficient to be taken as a unit. At the same time, since the Sun is always in the center of the system, and the observers are at the same distance from it (of course, observation from the planet’s surface is implied), a logical decision was made - to take the Earth’s orbit radius as the unit of cosmic distances. Further, everything is simple: the planet’s orbit is close to perfect circular, so the measurement error is minimal. Currently, the distance from the Earth to the Sun is 149.59 million km and is called the “astronomical unit” (au). Every year, due to a decrease in solar mass, an increase of 15 cm is recorded. Based on the foregoing, we can 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, contrasting with ancient beliefs about a flat shape. So, the average radius is 6371 km. However, this value is not entirely true. As you know, due to the inclination of the earth's axis at the poles there is always a large amount of snow and ice (the so-called "polar caps"). Because of them, a redistribution of the mass of the planet occurs, and the radius of the Earth, measured at the poles, differs from its value at the equator. The error is relatively small, but it is. For example, the equatorial radius of the Earth is 6378.1 km, but the polar radius is 6356.8 km. And recently, changes have been outlined relative to the poles caused by climatic anomalies. From the foregoing, it follows that when answering the question “What is the radius of the Earth?”, It is necessary to clarify what kind of measurement is implied. Only in this case can an exact answer be given.
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 hypothesis, at the early stage of the existence of the solar system, the Earth shared its orbit with another large planetoid the size of Mars and a mass equal to 10% of the earth. Once this hypothetical planet (Teia) collided with the Earth. As a result, part of its mass was thrown into Earth orbit, forming the Moon, and the remainder became part of the Earth, increasing the radius due to such an “additive”. Other prominent scientists claim that the collision occurred along a tangential path, so Tei’s destruction did not follow. In this case, the moon is part of our planet, thrown into a circular orbit. In turn, the radius, for obvious reason, did not increase, but decreased.
As you can see, sometimes it would be impossible to give direct answers to seemingly simple questions. As Pascal said, "The subject of knowledge is endless."