What if the earth inclined at 50 degrees?

Polar zone from 60 ° - 90 °

The earth

is our home in the universe and the only known place on which we can live. It is the largest planet in the solar system with a solid surface. Also in our solar system there is only liquid water in significant quantities on earth. About 71% of the earth's surface is covered by seas. The world on the earth's surface is a complex, interacting system of air, water, land and life that is still largely beyond our understanding.

In terms of size, the earth ranks 5th among the planets. It is the third planet in the solar system (as seen from the sun). The diameter of the earth is 12,765.28 km and its age about 4.6 billion years.

The earth's crust and the upper mantle below are solid. It has a thickness of 30 - 50 km, whereby it is sometimes only 12 km under the oceans. Both swim on the soft subterranean mantle below. Inside the earth is a core made of nickel and iron, to which we owe the magnetic field that protects the earth from high-energy particles that come from the sun and from the depths of the cosmos.

The earth is 149.6 million km away from the sun. It circles the sun in 365 days at a speed of 108,000 km / h. At the same time the earth rotates around its own axis. The rotation lasts 23 hours 56 minutes and 4 seconds. By turning around itself, the alternation of day and night occurs. Due to its very fast rotation, the earth is not ideally spherical, but deformed to an ellipsoid of revolution, i.e. somewhat flattened at the poles. Therefore, the equatorial diameter of 12,756 km is a good 42 km larger than the pole diameter of just under 12,714 km.


Data of the earth


12,765.28 km


40,075 km

Orbit around the sun

365 days, 6 hours, 15 minutes

Rotation time at the equator

23 hours, 56 minutes, 4 seconds

Distance from the sun

149.6 million km

Orbit inclination


Temperature (surface)

From -60 to + 50 ° C

the atmosphere

predominantly nitrogen and oxygen


about 6 billion people




The earth moves in an elliptical orbit around the sun, which is located in one of the focal points of the ellipse. The furthest point in the orbit, the Aphelion, and the closest point to the Sun, that Perihelion, are the two end points of the main axis of the ellipse. The mean value of the aphelion and perihelion distance is the major semi-axis of the ellipse and is about 149.6 million km. The passage of perihelion occurs around January 3rd and the passage of aphelion around July 5th. The earth needs 365 days, 6 hours, 9 minutes and 9.54 seconds for the sun to orbit. This period is also known as the sidereal year. The sidereal year is 20 minutes and 24 seconds longer than the tropical year from which the civil year of the calendar calculation is derived. The earth moves around the sun at an average orbit speed of 29.78 km / s, 30.29 km / s in perihelion and 29.29 km / s in aphelion. So it covers a distance the size of its diameter in a good 7 minutes. The direction of rotation of the earth is right-handed, that is, according to the rule of the direction of rotation in the solar system, it moves counterclockwise around the sun when viewed from the north pole of the earth's orbit plane.

The orbital plane of the earth becomes Ecliptic called. The ecliptic is inclined by a good 7 ° to the equatorial plane of the sun. The north pole of the sun faces the earth most strongly towards the beginning of September, the solar south pole again towards the beginning of March. Only around June 6th and December 8th is the earth briefly in the plane of the solar equator.

More information on the ecliptic can be found in the chapter on radiation budget.

The year results from the time of the earth's orbit around the sun.


Earth rotation



The earth is a rotating sphere with an inclined axis of the earth. It rotates clockwise relative to the fixed stars - towards the east - in 23 hours, 56 minutes and 4.09 seconds once around its own axis (sidereal day). So if you look at the north pole of the earth from space, the earth rotates counterclockwise.
The earth rotates 360 ° in one day, thus 360 ° in an hour: 24 = 15 °. It therefore takes 4 minutes to turn 1 °. As a result of the earth's rotation, the sun appears to be setting on the horizon to an observer.

Due to the orbital movement of the earth along its orbit in the same direction of rotation and the resulting slightly different position of the sun on consecutive days, a solar day, the time between two highs of the sun (noon), is slightly larger than a sidereal day and is according to the definition in 24 Divided into hours. The speed of the circular motion of the earth's equator is 464 m / s, i.e. 1,670 km / h.

Due to the speed of the earth's rotation and the resulting centrifugal force, the earth is slightly flattened at the poles and slightly arched at the equator. Compared to a sphere, the earth's radius at the equator is 7 km larger and the pole radius 14 km smaller. The diameter at the equator is about 43 km larger than that from pole to pole. Because of its proximity to the equator, the summit of Chimborazo is the point on the earth's surface that is furthest from the center of the earth.













The year results from the time of the earth's orbit around the sun, the day from the duration of the earth's rotation. But it is also clear that the same time does not prevail everywhere on earth at the same time. Originally, every place had its own time, called local time, which was based on the sun: when the sun reached its highest point above the horizon, it was 12 noon. With increasing national and international connections through railways and telegraphy, a world-wide uniform time system became necessary. The worldwide systematic time zone system is a consequence of the international agreement of the Greenwich meridian, named after the London borough, as the prime meridian at the Washington International Meridian Conference in 1884. This prime meridian, which is important for cartography, served from then on as the reference meridian for dividing the earth into time zones.

A time zone is formed by those parts of the earth's surface in which a uniform, state-regulated time and date apply. This time is the zone time belonging to the time zone and usually corresponds to the astronomical local time in the center of the zone. The ideal time zone is a closed area with a geographical difference of 15 °, to which the affected parts of the sea also belong, and extends from pole to pole. If you divide the earth into exactly 24 equal sections, you get 24 ideal time zones. These extend over 7½ degrees of longitude on both sides of the reference longitude, which ideally is a whole multiple of 15 ° with reference to the internationally agreed prime meridian. This has the following advantages:

  • The time difference to the neighboring time zones is ± 1 hour.
  • The zone time deviates at the zone boundaries only ± ½ hour from the mean solar time.

Today the zone times are predominantly to the coordinated universal time (UTCUniversal Time Coordinated) or Greenwich Mean Time (GMT) coupled, i.e. UTC is the current world time. It was introduced in 1972. The differences between UTC and neighboring zone times are constant, mostly whole-number hours. In the case of national or regional time zones, there is usually an indication of how many hours they deviate from UTC, e.g. UTC +1 corresponds to Central European Time (CET) or UTC +2 to Central European Summer Time (CEST) as well as Eastern European Time. The zone times are then specified relative to the generally applicable coordinated world time, for example as UTC + 1 h (= Central European Time CET) or UTC - 3:30 h (Newfoundland Standard Time). Today, UTC is the time scale for all times, especially in aviation and synoptic meteorology.

UTC is denoted by the letter Z in aviation or in NATO. Z stands for Zero (= zero). Therefore one speaks of Z-time or Zulu time (according to the word Zulu assigned to the letter Z in the ICAO alphabet). Z stands for zero meridian. In the meantime, however, the term Z-time is no longer used in aviation, only UTC is used. However, one can still find the Zulu times in weather reports (TAF / METAR); the specification 1350Z means 13:50 UTC. GPS-relevant values, for example for the calibration of navigation devices, are always marked with UTC, never with Z.

In some countries, there is also a change between normal zone time (normal time, English: Standard Time) and summer time (English: DST, Daylight Saving Time) approximately every six months. By using summer time, two zone times can occur in a time zone: normal (winter) and summer time. Both zone times can also be used at the same time in a time zone because the states concerned do not choose the same changeover dates. A time in UTC results in the corresponding Central European Time applicable in Germany, Austria and other Central European countries (CET) by spending 1 hour, and in summer from 04/01 to 09/30. applicable Central European Summer Time (CEST) by adding 2 hours.

The standard time in Germany, Poland, Austria, Switzerland, and Italy is Central European Time (CET), which is equal to UTC plus one hour. The military also calls this Alfa time (A). During summer time, Central European Summer Time (CEST) applies, which corresponds to UTC plus two hours, designated in the NATO area with the code Bravo time (B).

A time in the form 14:52 UTC + 1: 00 means 14:52 local time (local zone time) for a time zone that is one hour ahead of UTC, e.g. B. CET. UTC at this point in time is 1:52 p.m. The real time zones differ considerably from this, because they are also based on national borders. Most states today have chosen one of these 24 zone times as the legal time (or several zone times in states with a large east-west extension). An actual time zone is thus the sum of all states or parts of states with the same selected zone time and areas of the oceans that are always part of an ideal time zone.

A practical example from aviation: All times are specified internally as UTC time, e.g. B. UTC 13:52. A pilot who sees this time looks up in a directory which deviation applies to his whereabouts, e.g. B. LOT (Local Time) Berlin, i.e. local time Berlin = UTC +1. He now calculates: z. B. 13:52 + 1 = 14:52 local time in Berlin. However, this only applies in winter; in summertime it does not have to add one but two hours.

The date changes in each time zone when it is midnight (midnight / midnight) or when the date line is crossed (change between the time zones with UTC + 12h or UTC - 12h). A time zone is thus also identified by the same valid date.



The transition from bright day to dark night and vice versa usually lasts for several hours. This transition time between day and night is the "twilight" (dawn or dusk). In purely physical terms, the term twilight describes the period in which the sun is below the horizon, but the residual light scattered by the atmosphere is still visible in the sky. In particular, dust, gas and ice aerosols in the atmosphere, e.g. volcanic ash, can enormously intensify the "twilight" and ensure a wonderful play of colors. The sunset pictures painted by William Turner after 1816 should in reality at least also be from the intensely colored sunsets that were observable at the time, which can be traced back to the globally spread dust as a result of the Tambora volcano that erupted in the Pacific in 1815 and can be cited as an example.

The starting point for twilight is sunset, which in Central Europe takes about 3 - 4 minutes from the first contact of the sun disk with the horizon to its complete disappearance.

There are 3 phases of twilight:

  • The civil twilight starts immediately after sunset. During this phase, the brightness decreases continuously until the first bright stars or planets such as the evening star Venus become visible. This happens when the sun is about 6 ° below the horizon. During civil twilight you can still read the newspaper comfortably in the open air.
  • Then comes the nautical twilightat the end of which smaller stars and the outlines of the first constellations can be seen in the sky.Because the remaining scattered rays of the sun no longer provide sufficient brightness, additional artificial light is now required for most activities. Nautical twilight ends when the sun sinks 12 ° below the horizon.
  • The astronomical twilight joins it. The sunlight no longer reaches the higher layers of the air, which is why the sky appears really dark. It ends when the sun is 18 ° below the horizon. Then the night begins.

Only after the end of astronomical twilight can you actually see all the stars that can be seen with the naked eye. It is then really dark because the refraction of light in the atmosphere no longer leads to any brightening. By the way: With the naked eye you can see about 6000 stars under good conditions. Since half of the stars are above and the other half of the stars are below the horizon and therefore out of sight, you can answer the question of your children: "Do you know how many little stars there are ...": About 3000.

The length of twilight depends on the latitude of the earth you are at. The greater the distance to the equator, the longer the twilight lasts. Because the sun's path at the equator sinks very steeply in the evening, the sun quickly disappears below the horizon. However, the closer you get to the poles of the earth, the more pronounced the course of twilight becomes at certain times of the year. All travelers who come near the equator will notice how short twilight lasts at the equator.
Example: To reach the end of civil twilight, the sun must sink 6 ° below the horizon. The time required for this is 6. 4 minutes = 24 minutes.

In middle geographical latitudes, As in Baden-Württemberg, for example, twilight lasts significantly longer than at the equator. The sun sinks diagonally below the horizon here, so it has a longer way, which is why it takes longer until the end of civil twilight is reached.

In higher geographical latitudes such as northern Germany, the sun sets relatively late at the time of the astronomical beginning of summer, i.e. at the summer solstice, so that even at 11 p.m. you can sit comfortably in the beer garden without artificial light. Even at midnight it doesn't get really dark anymore. On the northern horizon you can still see a remnant of twilight. At that time, the sun does not sink more than 18 ° below the horizon at night, which is why the evening astronomical twilight is no longer ended, but merges seamlessly into the morning astronomical twilight. This phenomenon is known as twilight at midnight.

In the morning the 3 phases of twilight run in reverse order until the sun finally rises on the horizon.

  • With the introduction of SERA.2010, a new night definition was introduced in aviation on December 10, 2015. Since then, pilots in Germany need the twilight times for route planning instead of the previously common times of sunrise and sunset. According to Art. 2 SERA.2010, the night is defined as follows: The hours between the end of civil twilight and the beginning of civil dawn. Civil twilight ends in the evening and begins in the morning when the center of the solar disk is 6 ° below the horizon.



Inclination of the earth's axis

The axis of rotation of the earth around itself is not perpendicular to the plane that forms the elliptical orbit around the sun. Rather, it is currently inclined by 23 ° 26 'to this plane of rotation, the ecliptic. As a result, the angle of the solar radiation hitting the earth's surface changes on the earth's hemispheres in the different latitudes. In addition, different parts of the earth are irradiated to different degrees at different stages of the cycle. This leads to the seasons that largely shape the earth's climate.

The direction of the axis inclination currently falls within the ecliptical longitude of the constellation Taurus for the northern hemisphere. Seen from Earth, the sun at the summer solstice on June 21 will also be in this direction. Since the earth is undergoing aphelion two weeks later, summer in the northern hemisphere falls in the time of its orbit far from the sun. The distance of the earth from the sun thus has no noticeable influence on the seasons.

More on this can be found in the radiation budget chapter.

The inclination of the earth's axis



The earth is the only known planet in our solar system of which active volcanoes are known. The temperature inside the earth is around 4,000 ° C. A silicate coating is placed around a liquid core made of iron and nickel.Above this, a 10 to 30 km thick rock mantle forms the earth's crust. The surface of the earth is very young. In the past, erosion and tectonic processes have destroyed a large part of the earth's surface and created it again, eliminating almost all traces of early geological surface history, such as impact craters from meteorites or entire mountains. The traces of the early history of the earth have been largely erased. The earth was formed 4.5 to 4.6 billion years ago, but the oldest known rocks are only about 4 billion years old. The oldest fossils of living organisms, on the other hand, are less than 3.9 billion years old. Therefore there are no traces of the period in which life on earth originated.

71% of the earth's surface is covered with water. The earth is also the only planet on the surface of which water occurs in liquid form. Liquid water is the prerequisite for life as we know it. The heat storage capacity of the oceans is of particular importance for the stabilization of the earth's temperature. Liquid water is responsible for the erosion of the earth's surface, but also for the formation of weather over the earth's continents, a process that is unique in today's solar system.

More on this can be found in the chapter on water.


the atmosphere







Our blue planet

The composition of the Earth's early atmosphere, not its density, was comparable to that of Mars today: it contained hardly any oxygen, but a large proportion of carbon dioxide (CO2). This caused the earth to heat up, which led to the release of hydrogen and oxygen. These reacted with each other and thus created the water masses that today cover 2/3 of the earth. The first microorganisms formed in liquid water over a long period of time in a complicated development. Eventually the first forms of life began the CO present in the atmosphere2 to convert into oxygen. Since then, the carbon dioxide has been almost completely incorporated into carbonate rocks and to a lesser extent dissolved in the oceans or consumed by plants. Today, plate tectonics and biological processes cause a continuous flow of carbon dioxide into these various “CO2-Senken "and back again. Carbon dioxide in the atmosphere, along with other factors, most notably water vapor, is responsible for maintaining the Earth's surface temperature. This raises the average surface temperature by around 35 ° C above the level that would occur without this effect, namely from a frosty -21 ° C to a pleasant +15 ° C. Temperatures on the earth's surface range from -60 ° C to +50 ° C. Without an atmosphere, the temperature differences between day and night would be even greater.

Today's atmosphere consists of 77% nitrogen, 21% oxygen, 1% water vapor and 0.9% argon. The CO2-Content is around 0.038%. The presence of free oxygen is remarkable from a chemical point of view. Oxygen is a very aggressive gas and under "normal" circumstances it would combine quickly with other elements. However, the oxygen in the earth's atmosphere is constantly being produced and maintained anew by biological processes. Without life there would be no unbound oxygen.

The earth's atmosphere consists of several layers. It has a thickness of about 700 km. The mean air pressure at sea level is 1,013 hPa. The atmosphere protects the earth from the rays of the cosmos and the sun, and 2/5 of the rays are reflected back into space. During the night, the heat collected during the day is stored by the earth's atmosphere. When looking at the earth from space, the earth appears colored blue, hence the name of the "blue planet". The earth's atmosphere scatters the short-wave blue spectral component of sunlight about five times more than the long-wave red. When the sun is high, this causes the sky to turn blue. At the same time, red light is more strongly absorbed by the water of the oceans, which is why they appear blue when viewed from space.

More on this can be found in the Atmosphere chapter.



The astronomical seasons is the division of the year into 4 roughly equally long, 90 ° wide sections on the ecliptic, which are defined by two equinoxes ("equinoxes") and solstices ("solstices") that are 180 ° apart. The reason for the annual interplay of the seasons can be found in the orbital properties of the earth, i.e. in the celestial mechanical-related inclination of the rotating earth axis and thus the earth's orbit in relation to the (celestial) equator. The earth's axis - an (imaginary) line around which the earth performs its own rotation - is not perpendicular to the plane of the planet's orbit around the sun, the ecliptic, but rather it deviates from the perpendicular by an inclination of about 23.5 °. This "skewness of the ecliptic" is therefore also the cause of the equinoxes and solstices.

The seasons divide the period of an earth year - one orbit of the planet earth around the sun - so in our latitudes into 4 different periods, each of which differ from one another by their characteristic properties: spring, summer, autumn and winter. The seasons are opposite in the northern and southern hemispheres - e.g. summer in the south, winter in the northern hemisphere, and vice versa.

Due to the different orbital speeds of the earth, the length of the seasons is not exactly a quarter of a year, but varies slightly. Spring lasts 92 days and 18 hours in the northern hemisphere, summer 93 days and 16 hours, autumn 89 days and 20 hours, and winter almost exactly 89 days.

In the tropics, the seasons cannot be distinguished from one another in this way. A distinction is made there between the dry season and the rainy season.

The change of the seasons

While the earth revolves around the sun in the course of a year, the inclination of the earth's axis remains constant. That is why the radiation conditions in the northern and southern hemispheres of our planet change continuously over the course of the year. As a result, the zenith of the sun moves back and forth between the northern and southern tropics (hence the name of the tropics).

This apparent migration of the sun is described in more detail in the Tropics chapter.

As already mentioned, the inclination of the ecliptic, in addition to the distance from the earth to the sun, is decisive for solar irradiation and thus the energy gain of the earth's surface over the course of the year and also causes the seasons, which are more pronounced in middle and high geographical latitudes. The sun therefore describes a slightly different arc in the sky on each new day - the so-called day arc, i.e. the imaginary line in the sky that the sun travels on its daily path from sunrise to sunset. This arc is quite small and flat in autumn and winter, but in spring and summer it is much longer and protrudes increasingly higher over the horizon. This changes the duration and intensity of irradiation as well as the angle at which sunlight hits the earth's surface in the various latitudes of the earth. For example, here in spring and summer the duration of sunshine is longer than in autumn or winter and the solar radiation hits the surface of the earth much more steeply (vineyard effect). Therefore, the earth's surface experiences a much higher energy input, which in turn leads to a warming of the corresponding earth hemisphere during this period.

As a result, the position of the sun relative to the earth changes with the seasons and with it the angle of incidence of sunlight. Around noon, this can range from vertical (90 °) within the tropics or at the equator to horizontal (0 ° = sun does not appear or only partially on the horizon) within the polar circle or at the poles.

For example, the astronomical or calendar winter forms the section between the winter solstice on 21/22. December and spring equinox on 21/22 March, i.e. the sun moves northward on the ecliptic until the spring equinox. The day arcs of the sun between its rising and setting as well as the length of the day increase again, the midday height of the sun rises above the horizon and the angle of incidence of solar radiation increases again. Nevertheless, in Central Europe it is on average even colder at first, which is why January is usually the coldest month of the year in Germany. This is due to the so-called thermal inertia of the climate system (earth's surface and atmosphere): The middle and high geographical latitudes cannot benefit from the increasing solar radiation at the time, as this energy gain is still significantly exceeded by the energy loss due to the radiation. Therefore, the conflict between subtropical and polar air masses lasts until spring and gives us, depending on which air mass prevails for a long time, a mild or severe winter.

Because the days get longer again after the winter solstice, it has been an important festival in many ancient cultures since the Stone Age at the latest, which was sometimes celebrated before or after the actual solstice. The ancient Teutons then celebrated their "Yule Festival", while in ancient Rome December 25th was one of the most important holidays, which was celebrated in honor of the "God of the invincible sun" ("Sol invictus"). Not least in this tradition, the time of the winter solstice was adopted by the Catholic Church for the Christian Christmas festival.

The highest point of the sun is reached at the time of the summer solstice, the calendar beginning of summer. Due to the thermal inertia of the earth's atmosphere, the warmest months only appear with a delay of 1 to 2 months - in fact, in summer the duration of sunshine is already decreasing from day to day.

The most extreme effects of the seasons can be found in higher geographical latitudes beyond the northern or southern Arctic Circle. There the phenomenon of the polar day or the polar night occurs, i.e. the polar areas are illuminated by the sun every six months either permanently (the sun does not set) or not at all (the sun does not rise).

The distance of the earth from the sun, on the other hand, has no perceptible influence on our seasons. In fact, at the beginning of January, shortly after the start of winter in the northern hemisphere, the earth is around 5,000,000 km closer to the sun than in summer.

In terms of calendar, the seasons are assigned 3 calendar months:

  • spring: March May
  • summer: June August
  • autumn: September - November
  • winter: December - February.

However, the meteorological seasons are defined differently. Since winter weather often prevails in the middle latitudes before the sun is at its lowest point and it is more comfortable for statistical purposes, meteorologically the months December, January and February make up winter, March, April and May make up spring, June, July and August make up Summer as well as September, October and November the autumn. The meteorological summer begins on June 1st, for example.

More on this can be found in the radiation budget chapter.



The angle of incidence of the sun and the length of the day
Author: Thomas Steiner - wikicommons

The solar radiation hits the different latitudes of the earth at different angles due to the inclination of the earth's axis. At the equator, the rays usually hit the ground vertically at noon, while at the poles the sun is oblique or even below the horizon during the polar night (see figure on the left).

The position of the sun in relation to the earth changes with the seasons and with it the angle of incidence of the sunlight. Around noon, this can range from vertical (90 °) within the tropics to horizontal (0 ° = sun does not appear or only partially on the horizon) within the arctic circle.

The sun's rays heat the earth much more strongly at the equator than at the poles. Due to the temperature differences caused by irradiation, recurring climatic conditions arise, such as winter and summer, a certain amount of precipitation in summer, or a certain average air temperature.

The different climatic conditions that occur regularly in certain areas are summarized and described in climatic zones. Climate zones are large areas of the earth in which the climate is similar or relatively uniform, the so-called climate belts of the earth. They can be determined according to the radiation conditions, thermal or the effects of the climate, e.g. on vegetation. This in turn heats the air differently. Warm air rises because of its lower density and cools down again at altitude. The resulting air circulation compensates for these temperature differences through air movement and wind. This ultimately leads to different climatic conditions in the different latitudes.

The earth is accordingly divided into different climatic zones, which extend around the earth in an east-west direction from the poles to the equator. As a rule, the climatic zones are belt-shaped and circular at the poles. They are differentiated from one another on the basis of different basic climatic conditions. The details of the climate classification should not be considered here.

Simplified, there are 4 large climate zones:

  • The polar regions are, on the one hand, the region within the northern polar circle (60 ° N), the Arctic, and the region within the southern polar circle (60 ° S) with the continent of Antarctica in the southern hemisphere of the earth. The polar regions of the earth are cold deserts. Temperatures are below or just above the freezing point all year round. The rainfall is low. The solar irradiation is greatly reduced - on average 40% less than at the equator, since the sun's rays usually only come in very shallowly here. Due to the change in the angle of the earth to the sun, the length of the day fluctuates the most here. In summer it comes to polar day, in winter to polar night. Plant growth (vegetation) is only possible here for a few months of the year and sometimes only sparsely. The conditions for life in these areas are therefore very harsh. In addition to the cold climate with snow and ice, a special characteristic of the polar regions is the polar day, which lasts up to six months, with the midnight sun or the polar night, but also the polar lights.

  • The temperate climatic zone extends from the Arctic Circle to the 40th parallel. The temperate zone shows great differences between the seasons, which however decrease as the equator approaches or change into the alternation of dry and rainy seasons. An essential feature are the differences between day and night, which vary greatly depending on the season. The length of the day varies between 8 and 16 hours. In the temperate zone, the sun's rays are shallower, which is why it is significantly cooler on average compared to the subtropics. The middle widths are in the west wind zone. The climate is therefore characterized by less frequent extremes, an even distribution of precipitation over the year with a long vegetation period - hence the name "moderate". With values ​​around 800 mm, the temperate zone has the second highest amount of precipitation after the tropics. At the same time, the weather is very unstable. The vegetation is characterized by coniferous, mixed and deciduous forests, with the coniferous forests becoming fewer and fewer towards the south.

  • The subtropics extend from the 40th parallel to the tropics. They show high summer and moderate winter warmth. They receive a high level of irradiation all year round, but especially in summer, since the sun is almost perpendicular to the earth's surface around noon. Due to the special circulation conditions in the atmosphere, these areas receive little moisture at the same time (see trade winds). As a result, the cloud cover is relatively low, which favors the high level of radiation. That is why most of the world's deserts can be found in this zone. In winter, the radiation in these areas decreases significantly and it can become very cool and humid at times. The vegetation ranges from a particular diversity of species, e.g. in the Mediterranean region, through dry savannas to barren or even completely missing vegetation in deserts such as the Sahara.

  • The tropics lie between the equator and the tropics. The sun's rays hit the earth almost vertically at noon almost all year round, so that it is very warm in these areas. In the tropics, day and night are always roughly the same length (between 10.5 and 13.5 hours). Due to the high temperatures, large amounts of water evaporate, which is why the humidity is very high. In the course of the day, this leads to frequent and dense clouds, which are caused by strong evaporation. The radiation from the sun's rays is weakened as a result. There is thus a time-of-day climate: the daily temperature fluctuations are greater than the annual ones. The precipitation-determining phenomenon in the tropics is the trade wind circulation and its seasonal shift. The Passatz circulation causes the constant so-called zenital precipitation around the equatorial convergence zone.The convergence zone can almost stand still - in the Pacific and Atlantic - or move cyclically over the entire tropics over the course of the year, as in the area from Central Africa to the Malay Archipelago. Accordingly, areas are created with a range of precipitation from always moist to dry. In addition, the winds of circulation, trade winds and monsoons, act locally onshore and then also cause precipitation. Climatic seasons only exist in the humid tropics, so that only dry and rainy seasons can be distinguished. The wet savannahs, which are located north and south of the large rainforests, are typical of the humid tropics. They are characterized by their wide grasslands. Examples are the African savannah and the Pantanal in southern Brazil and Paraguay. The large, very species-rich rainforests, such as those of the Amazon region, are typical of the always humid tropics that are located around the equator.



Global energy balance

The energy balance of the earth is essentially determined by the radiation from the sun and the radiation from the earth's surface or atmosphere, i.e. by the radiation balance of the earth. The remaining contributions, totaling around 0.02%, are significantly below the measurement accuracy of the solar constants and their fluctuations in the course of a sunspot cycle. The geothermal energy contribution generated by radioactive decay accounts for around 0.013%, around 0.007% comes from human use of fossil and nuclear fuels and around 0.002% is caused by tidal friction.

The average albedo of the earth is 0.367, with a significant proportion being attributable to the clouds in the earth's atmosphere. This leads to a global effective temperature of 246 K (−27 ° C). However, due to a strong atmospheric greenhouse effect, the average temperature on the ground is around 288 K (15 ° C), with the greenhouse gas water vapor making the main contribution.

More on this can be found in the radiation budget chapter.
In addition, the chapter on themodynamics may also be of interest in this context.