The earth

20/09/2020

To understand the environment in which we move and in which we carry out all our daily activities, we have to know in advance the main characteristics of it.

• Geographical data of the Earth

- Diameter in Ecuador: 12,756 km

- Diameter at the poles: 13,713 km

- Circumstance in Ecuador: 40,075 km

- Circumference at the poles: 39,942 km

Throughout history, there have been different theories about what the shape of the Earth was like, even saying that it was flat. With technological advances, it has been possible to determine the exact shape of planet Earth. The surface of the Earth is characterized by not having a homogeneous shape since it contains seas, rivers, mountains, volcanoes, etc. For this reason and for a simpler study, the following models of representation of the Earth were taken into consideration: spherical, ellipsoid and geoid,

Earth movements: our planet is a star that does not remain immobile in space, but is in continuous movement. The Earth's axis is the imaginary line that crosses the Earth from the North Pole to the South Pole and around which the Earth rotates in its rotational motion. Two main types of movements can be distinguished: rotation and translation. The first is the movement that the Earth executes by turning on itself from west to east. A complete turn is called a sidereal day, which corresponds to approximately 24 hours. The second is the movement by which the planet Earth rotates in an orbit around the Sun. It takes approximately 365 days to travel that orbit. Every four years there is a year that has 366 days, which is called a leap year.

Magnetic North: The Earth has a magnetic behavior opposite, and these do not coincide with the geographic poles. Therefore, we will have to take into account that the geographical north and the magnetic north of the Earth are not the same. In this way, as they are not located at the same point, the angle that is formed between geographic north and magnetic north is called magnetic declination or variation. Highlight that this data is different at each point on the earth's surface.

Earth references: in order to be able to use a system in which the position of a certain point on Earth (geographical coordinates) can be precisely specified, it is necessary that there be a series of fixed references in order to make this determination. Meridians are imaginary semicircles perpendicular to the Equator that join both poles from north to south. The reference meridian is Greenwich Mean Time. Longitude is the angular distance between a given point on the earth's surface and the reference meridian, measured along the parallel at which that point is located. Geographic longitude is determined east or west relative to the reference meridian (Greenwich). Parallels are imaginary circles parallel to the Equator and perpendicular to the meridians. Unlike the meridians, the parallels are not all the same size. The Equator is the reference parallel that divides the Earth into two equal hemispheres, the northern hemisphere and the southern hemisphere. Latitude is the angular distance between a certain point on the earth's surface and the reference parallel (Equator) measured along a meridian where that point is located. Geographic latitude is measured between 0 • and 90 • and is determined north or south with respect to the Equator. Geographic coordinates is a reference system that through the use of longitude and latitude determines the position of a point located on the earth's surface. When expressing a coordinate, the first measurement is in reference to latitude and the next to longitude.

Local time, GMT and UTC: the local time of each country is determined according to its daylight hours to achieve energy savings in addition to other reasons; This is why in each country or area there is a different local time. GMT (Greenwich Mean Time) is the mean solar time at the Royal Observatory in Greenwich (London), which by convention is 0 degrees longitude. For years this was adopted as the official time around the world, since clocks were based on the movement of the Earth on itself and on the Sun. Over the years they realized that the Earth could not considered as an exact clock since the influence of the tides made the constant of its rotation vary. With the development of the atomic clock, in 1972 the term UTC (Universal Time Coordinate) was adopted based on atomic time, in order to use a common reference time and not the local hours of each country. In the military field and in air navigation, Coordinated Universal Time is designated as Zulu time, represented by the letter Z in the International Phonetic Alphabet.