TRANSLATIONAL MOVEMENT OF THE EARTH: CHARACTERISTICS, CONSEQUENCES - PHYSICAL - 2025

The translational movement of the Earth is the displacement that the planet makes around the Sun. Along with the rotational movement around its own axis, it is one of the two main movements that it carries out in space. It is periodic, since in little more than a year the Earth completes an orbit.

The movements of the Earth affect the daily life of all living beings that inhabit it. These movements have always been reasons for discussion and debate among human beings, having influenced the scientific thought of every civilization that has existed.

Figure 1. The movement of terrestrial translation gives rise to seasonal changes. Source: Public Domain Pictures.

Great scientists and astronomers such as Nicholas Copernicus, Fiolaus of Crotona, Hipparchus of Nicaea, James Bradly Johannes Kepler, Isaac Newton were interested during their research in the movements of the Earth, including translation.

characteristics

Among the most important characteristics of the translational movement are:

- The orbit described by the Earth is elliptical and with the Sun in one of the foci, as determined by Kepler's laws of planetary motion. An observer at the north pole would say that it does it counterclockwise (left-handed).

- The total length of the elliptical orbit is about 930 million kilometers.

- The eccentricity of this ellipse is so small (it has been calculated at 0.017), that the Earth's orbit can be approximated quite well as a circumference whose approximate radius is about 150 x 10 ⁶ km. If the orbit is drawn accurately, it cannot be visually distinguished from a circumference. In fact, the semi-minor axis of the orbit is approximately 99.98% of the length of the semi-major axis.

- The Earth follows this path at a rate of about 30 km / s on a plane called the ecliptic, whose perpendicular when passing through the center of the Earth defines the poles of the ecliptic. The axis of rotation of the Earth is inclined with respect to this line about 23.5º, exposing the northern hemisphere more to the solar rays during the summer months and vice versa during the winter.

Origin

The cause that the Earth describes an elliptical orbit around the star king is in the gravitational attraction that this exerts on it and in the nature of this force, which depends on the inverse of the square of the distance 1 / r ².

Towards the end of the 16th century, the German astronomer Johannes Kepler (1571–1630) discovered that the actual trajectories of the planets around the Sun were elliptical. And this fact later provided Isaac Newton with the basis for establishing the universal law of gravitation.

An ellipse is the locus of points at which the sum of the distances to two points called foci is constant. In Earth orbit the Sun is in one of the foci.

The more flattened an ellipse is, the more different are the semi-major axis and the semi-minor axis. The eccentricity of the ellipse is the parameter that measures this characteristic. If it is 0, which is the smallest possible value, it is a circle.

Even having a small eccentricity, the Earth passes during the month of January through a point where it is closest to the Sun, called perihelion, 147.1 million kilometers from the Sun. And the aphelion is the farthest, it occurs in July and measures 152.6 million km.

The period of the Earth's translational motion

Kepler's laws for planetary motion were established empirically from countless measurements. They establish that:

- Planetary orbits are elliptical

- The area swept by the radius vector during a certain time interval is the same throughout the movement.

- The square of the period (T ²) is proportional to the cube of the average distance between the planet and the Sun (r ³), being C the constant of proportionality, the same for any planet:

The value of C can be calculated using the already known data for the Earth and its units in the International System are s ² / m ³.

Consequences

Earth movements are closely linked to the measurement of time and seasonal changes in climate, in which the temperature and the hours of light and darkness vary. Both factors and their periodicity have led to human activities being governed by times established in the calendars.

The translational movement defines the length of the year, during which the seasons follow each other and the stars in the sky change. During the summer, those that are visible at night, "rising" in the east and "setting" in the west in the morning, do the opposite during the winter.

Likewise, the climate undergoes changes according to the time the earth's surface is exposed to sunlight. The stations are the combined effect of the earth's translational movement and the inclination of the axis of rotation with respect to the orbital plane.

The calendar

The Earth completes a complete revolution around the Sun in 365 days, 5 hours, 48 ​​minutes and 45.6 seconds. This assuming that the Sun is taken as a reference, which will be considered as fixed.

This is the definition of "solar year" or "tropical year", the time between two consecutive vernal equinoxes. The equinoxes are times of the year when day and night have the same length anywhere on the planet. They occur on March 22 and September 22.

As this time exceeds 365 days, but it is necessary to maintain solstices and equinoxes around the same days of the year and that it has a whole number of days, the concept of a "leap year" is introduced.

Each year about 6 more hours are added, so that after 4 years 24 hours or a full day have been accumulated: a year of 366 days or leap. The extra day is allocated to the month of February.

On the other hand, the "astronomical year" is measured by the time it takes for the Earth to pass successively twice through the same point. But this year is not the one that defines the calendar.

Seasons and land zonal divisions

The earth's translational motion, plus the inclination of the axis of rotation with respect to the poles of the ecliptic (obliquity of the elliptical), causes the planet to move away from or closer to the sun and vary the exposure to solar rays, giving rise to to the seasons of the year: the equinoxes and solstices.

The intensity and duration of seasonal changes vary depending on where on Earth. In this way the following zonal divisions are defined:

- The equator

- The tropics

- The temperate zone

- The polar circles.

- The poles

At the equator, the sun's rays have maximum verticality and the days and nights have the same duration throughout the year. At these points, the variations in climate depend on the height above sea level.

As it moves towards the poles, the incidence of the solar rays is more and more oblique, giving rise to changes in temperature, as well as the inequality between the length of days and nights.

Solstices

The solstices are two times of the year that occur when the Sun reaches its highest or lowest apparent height in the sky, and the length of day or night is the maximum of the year (summer and winter solstice respectively).

In the Northern Hemisphere they take place on June 20-23 in summer and December 21-22 in winter. In the first case, the sun is at its maximum height at noon on the imaginary line known as the Tropic of Cancer (longest day of the year) and in the second its height is minimum.

Figure 2. Schematic of the Earth during the summer solstice. The sun's rays illuminate the north pole, while the south pole remains dark. Source: Wikimedia Commons.

The dates have some small variations due to another earth movement: the precession.

At this time, the sun's rays strike with more intensity in the northern hemisphere (summer) and conversely in the southern hemisphere (winter). For its part, the Sun is always visible at the north pole, while the south pole is not illuminated, as seen in the figure.

For the Southern Hemisphere the situation is reversed: for December 20-21, the sun is at its highest point at noon over the Tropic of Capricorn, being the summer solstice to give way to the hot season. And for June 20-21 it is at its minimum and it is the winter solstice (longest night of the year).

During the winter solstice the north pole remains dark, while at the south pole it is summer and daylight is permanent.

Figure 3. During the winter solstice in the northern hemisphere, the sun's rays illuminate Antarctica. Source: Wikimedia Commons.

Equinoxes

During the equinoxes, the Sun reaches its zenith or highest point perpendicular to the equator, therefore the solar radiation falls with the same inclination in both hemispheres.

The times when this occurs are March 21 - 22: spring equinox for the northern hemisphere and autumn for the southern hemisphere and September 22-23 vice versa: autumn for the north and spring for the south.

Figure 4. During the equinox the days and nights have the same duration. Source: Wikimedia Commons.

During the equinoxes the Sun rises in the East and sets in the West. In the figure it is observed that the illumination is distributed uniformly in both hemispheres.

The duration of the four seasons is approximately the same in days, on average about 90 days with slight variations.

References

1. Aguilar, A. 2004. General Geography. 2nd. Edition. Prentice Hall. 35-38.
2. How fast is the Earth moving? Recovered from: scientificamerican.com
3. Oster, L. (1984). Modern Astronomy. Editorial Reverte. 37-52.
4. Tipler, P. Physics for Science and Engineering. Volume 1. 5th. Edition. 314-316.
5. Toussaint, D. The Earth's Three Motions. Recovered from: eso.org.