In the Solar System there are nine or, given the latest agreement in the scientific environment, eight planets (Pluto in 2006 lost this honorary title).Among them, special attention should be paid the third planet - Earth.Its most important feature, known to every schoolchild - the ability to maintain a simple and highly organized life.The estimated age of the planet is more than 4 billion years, which is consistent with the theory of planet formation from the gas clouds surrounding the sun.
There are a number of important characteristics, which should be familiar to everyone who has decided to replenish their knowledge about their home planet.In this paper, we highlight these characteristics.
Since the beginning of the astronomical observations of solar system objects, and public acceptance of the heliocentric model of the world was a very serious question to measure distances in space.Typical "Earth" measurements (meters, miles) for this problem is not suitable.It is worth noting that, although the distance from the Earth to the Moon was already known in the 17th century, it seemed insufficient for making a unit.At the same time, because the sun is always in the center of the system, and observers - at the same distance from it (of course, refers to the observation from the surface of the planet), it was made a logical decision - to accept per unit cosmic distances radius of Earth's orbit.Then everything is simple: the planet's orbit 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 reduction of its fixed solar mass increase of 15 cm. Based on the above, we can calculate the distance from the Sun to Pluto - 39.4 AUetc.
What is the radius of the Earth, everyone knows.The saying "Earth is a sphere" is now a symbol of time, as opposed to ancient beliefs of the flat shape.Thus, the average radius is 6371 km.However, this value is not quite true.As is well known, thanks to the inclination of the Earth's axis at the poles is always present a large amount of snow and ice (the so-called "polar caps").Because of them, there is a redistribution of mass of the planet, and the radius of the Earth, measured at the poles, is different from its value at the equator.The error is relatively small, but it is.For example, the Earth's equatorial radius of 6,378.1 km, but the pole is 6356.8 kilometers.And recently there have been changes with respect to the poles due to climatic anomalies.From the foregoing it follows that the answer to the question "What is equal to the radius of the Earth?", It is necessary to clarify what kind of measurement is implied.Only in this case it is possible to give a precise answer.
Few people know that the existence of our planet's natural satellite - the Moon - indirectly could affect the Earth's radius.According to one hypothesis, at an early stage of the solar system orbit the Earth its shared with other large planetoid the size of Mars, and a mass equal to 10% of the earth.Once this hypothetical planet (Theia) collided with Earth.As a result of its mass was ejected into orbit to form the Moon, and the rest became a part of the Earth, due to a "supplement" to increase the radius.Other prominent scholars argue that the collision occurred at a tangent path of destruction so Teyi followed.In this case, the Moon is part of our planet, stranded on a circular orbit.In turn radius, for obvious reasons, has not increased, but decreased.
As you can see, sometimes, seemingly simple question is impossible to give direct answers.As Pascal said, "The object of knowledge is infinite."
