Looking at a globe or world map, we will see a grid of thin blue lines. Among them will be the main parallels of the Earth: the equator, the two Arctic Circles, as well as the Northern and Southern Tropics. We will tell you more about them in our article.
Main parallels of the Earth
Everything on the model of our planet is, of course, conditional and imaginary. All of them were mapped scientifically and practical purpose. However, among them there are five very important parallels: the equator, the Arctic Circles, the Southern and Northern Tropics. The existence of all these fictional lines is directly related to the real ones. natural laws(physical and geometric). And knowledge about them is extremely important for a comprehensive study of geographical science.
The equator divides our planet into two equal halves- North and the location of this line is strictly perpendicular to the axis earth's rotation. This is the longest parallel to our planet: its length is 40 thousand kilometers. In addition, the Sun at the equator is at its zenith twice a year, and the entire equatorial region of the Earth receives greatest number solar radiation per year.
Polar circles are parallels that limit such phenomena as polar day and polar night on the surface of the planet. These lines correspond to latitude 66.5 degrees. In the summer, residents living beyond have the opportunity to contemplate polar days (when the Sun does not set below the horizon at all). At the same time on another celestial body and does not appear at all (polar night). The length of polar days and nights depends on how close a particular location is to the planet's poles.
There are two tropics on our planet, and they were not created by chance. Once a year, the Sun is at its zenith above one of them (June 22), and after another six months - above the other (December 22). In general, the word “tropic” comes from the Greek tropikos, which translates as “turn.” Obviously, we're talking about about the movement of the Sun across the celestial sphere.
The Tropic of the North is located north of the equator. It is also called the Tropic of Cancer. Where did this name come from? The fact is that two thousand years ago the Sun during the period summer solstice was located precisely in the constellation Cancer (now the celestial body at this period of the year is in the constellation Gemini).
The exact latitude of the Northern Tropic is 23°26′ 16″. However, its position changes over time due to changes in the tilt of the earth's axis, nutation and some other geophysical processes.
Geography of the Tropic of the North
The Northern Tropic crosses three oceans (Pacific, Atlantic, Indian) and three continents (Eurasia, Africa and North America). The parallel runs through the territories of twenty states, including Mexico, Algeria, India and China.
There are a number of cities located at the latitude of the Tropic of Cancer. The largest of them:
- Dhaka (Bangladesh);
- Karachi (Pakistan);
- Bhopal (India);
- Guangzhou (China);
- Medina (Saudi Arabia).
In addition, the Tropic of Cancer crosses several large rivers: Nile, Ganges, Mekong, etc. A little south of this parallel is Mecca - the main sacred place of all Muslims in the world.
Southern Tropic and its geography
23° 26′ 21″ - this is the latitude at the beginning of this century. The position of this line is also not constant over time. The tropic moves very slowly towards the earth's equator.
The parallel also has its second name - the Tropic of Capricorn. It crosses only 10 states, which are located on three continents of the planet ( South America, Africa and Australia). Largest city, located in the tropics - Brazilian Sao Paulo. It is curious that this parallel crosses Australia almost in the middle, thereby causing a significant aridity of the climate of this continent.
The Tropic of Capricorn is usually marked on the ground in various ways. The most impressive sign announcing the passage of the Southern Tropic is located in Chile. A huge 13-meter monument was built near the city of Antofagasta in 2000.
In conclusion
Now you know where the Northern Tropic is located, what countries and continents it crosses. It is also called the Tropic of Cancer. It marks the northern latitude above which the Sun can rise to its zenith. Mirror positioned to it in Southern Hemisphere Tropic of Capricorn.
Why do the seasons change?
The change of seasons occurs due to the rotation of the Earth around the Sun.
What time of year is it summer in the southern hemisphere?
When we have summer, it is winter in the southern hemisphere.
Why are the seasons different in the Northern and Southern Hemispheres?
The seasons in the Northern and Southern Hemispheres are not the same because earth's axis inclined to the orbital plane at an angle. As the Earth moves around the Sun, different territories receive different quantities heat.
Questions and tasks
1. How does the amount of heat received by the earth’s surface change with changes in latitude?
The amount of heat received by the earth's surface decreases in the direction from the equator to the poles.
2. Using Figure 109, compare the average annual temperature in the north and south of Eurasia?
The average annual temperature in the north of Eurasia is -100C, in the south - +200C. Thus, in the south of the continent it is 300C warmer.
3. What are the tropics and polar circles. What is their latitude?
The Northern and Southern Tropics are parallels of 23.5° N. w. and 23.5° S. sh., on each of which the sun's rays fall vertically once a year - on June 22 and December 22. The Northern and Southern polar circles are parallels 66.5° N. w. and 66.5° S. sh., where once a year (December 22 and June 22) there is a polar day and a polar night.
4. What are the dates of the summer and winter solstices, spring and autumn equinoxes?
The summer solstice is June 22, the winter solstice is December 22. The spring equinox is March 21, the autumn equinox is September 23.
5. How many times a year and on what days do the sun’s rays fall vertically on the equator, on the tropics?
The sun's rays fall vertically on the equator on the equinoxes - March 21 and September 23. The sun is at its zenith Northern Tropic June 22, over the Southern Tropic - December 22.
6. Where can you observe the polar day and polar night? What is their minimum and maximum duration?
Polar days and nights are observed in cold zones. In summer, during the polar day, the sun does not hide behind the horizon, but its rays only glide across the surface, slightly heating it. On a winter polar night, the sun does not appear above the horizon at all. The duration of polar days and nights increases from polar circles to the poles. At the polar circles themselves it is equal to one day, and at the poles - six months.
7. What zones, tropics and polar circles divide the Earth’s surface? In what zones is the territory of Russia located?
Because of uneven distribution The light and heat coming from the Sun divide the earth's surface into five zones of illumination - hot, two moderate, two cold. The boundaries between them are the tropics and the polar circles. The territory of Russia is located in temperate and cold zones.
8. Why are there white nights in St. Petersburg at the beginning of summer?
This city is located at the 60th parallel, which is six degrees south of the Arctic Circle. This reference mark, where in summer period The polar day is coming. At this time, the sun almost never sets beyond the horizon. The reason for this phenomenon is the tilt of the Earth's axis to its orbit. IN summer time Northern Hemisphere The Earth is tilted towards the Sun, which explains the very long day at the end of the first summer month V northern latitudes. The sun, having just managed to hide behind the horizon, begins to emerge from behind it again. That's why there are white nights in St. Petersburg.
Complex and not a typical ball. This can be proven by comparing the equatorial and polar radii. The distance from the center of the planet to its equator is called the semimajor axis (or equatorial radius) and is 6,378,245 m. The distance from the center of the planet to its pole is called the semi-minor axis and is 6,356,863 m. Consequently, the semi-major axis is approximately 22 km larger than the minor axis. The Earth is slightly flattened at the poles (polar compression).
Total surface area globe is 510 million sq. km. The length of the equator is 40,000 km.
Its only satellite orbits the Earth at a distance of 384.4 thousand km. The period of revolution of the Moon around the Earth and around its axis coincide, therefore the Moon is turned to the Earth on one side, and the other is not visible from the Earth.
Terrestrial magnetism
The earth has magnetic field, clearly manifested in the effect on the magnetic needle, which, freely suspended in space, is always installed along the magnetic power lines, converging in magnetic poles. The magnetic field (magnetosphere) reliably protects all life on the surface of the Earth from the harmful effects of charged cosmic particles.
Earth's movement and its indicators and consequences
It has now been established that the Earth has four types of motion.
- Movement together with around the center of the Galaxy. One galactic year (time during which solar system makes one revolution) is 280 million years.
- Movement around the Sun in an orbit shaped like an ellipse, close to a circle with a radius of 149 million km. The speed of the Earth is about 30 km/sec. The earth completes a full rotation in 365.25 days. This time is called sidereal year . The Earth's axis is invariably inclined to the orbital plane at an angle of 66.5 degrees. This provides different position planets towards the Sun during the year, affects the angle of incidence sun rays and, as a consequence, the change of seasons.
During full turn The Earth around the Sun has particularly noteworthy dates:
- June 22 – summer solstice day . On this day the earth's axis is tilted North Pole to the Sun. The sun is at its zenith above the parallel of 23.5 degrees north latitude. Therefore, the Northern Hemisphere receives much more heat than the Southern Hemisphere. The entire hemisphere experiences the longest day. And in the northern circumpolar region(from 65 degrees N to the pole) The sun does not set and polar day is observed. In the Southern Hemisphere the picture is the opposite: the longest night, and in the subpolar region (from 65 degrees S to South Pole) The sun doesn't rise at all. Parallels of 65 degrees in both hemispheres are called polar circles . If you move from the polar circles to the poles, the duration of polar days and nights increases. At the poles it is 6 months. The parallels of 23.5 degrees in the Northern and Southern Hemispheres are called tropics .
- December 22 – winter solstice day . On this day, the Sun is at its zenith over the southern tropics (23.5 degrees S). The Southern Hemisphere has the longest day, and the Northern Hemisphere has the shortest.
- March 21 (in the Southern Hemisphere September 23) - vernal equinox, September 23 (in the Southern Hemisphere March 21) - autumn equinox . These days the Sun is at its zenith above the equator. In both hemispheres, day is equal to night.
3. The movement of the Earth around its axis . around its conventional axis from west to east with a full rotation during sidereal day, by which we mean the time of a complete revolution of our planet around its axis relative to the stars, considering them to be infinitely distant. A sidereal day is approximately 24 hours. The places where the conventional axis intersects the surface of the Earth are called poles. This movement is associated with the change of day and night on Earth. The time from sunrise to sunset is called day, and from sunset to sunrise is called night. Between daylight and darkness of the night There is a time of twilight, when the Sun has not yet risen, or has just set and illuminates the air above the horizon, and due to this, objects are easily distinguishable. The duration of twilight depends on the angle at which the apparent movement of the Sun occurs. The closer to the equator, the shorter the twilight. The time when evening twilight meets morning twilight is called “white nights.”
The daily rotation of the Earth is the reason not only for the change of day and night, but has another important consequence– deflection of any moving body relative to the Earth’s surface. Each moving body, under the influence of inertial forces, strives to maintain the direction of its movement. While on Earth, we evaluate any movement relative to earth's surface, which we assume to be stationary. In fact, the Earth rotates and the body, trying to maintain the direction of its movement, deviates in relation to the earth's surface. The force that deflects the body in this way is called the “Coriolis force” (in honor of the French scientist G. Coriolis). Although this term is not entirely fair, because... in fact, there is no force, and the deflection is associated only with the moving frame of reference. It is more correct to use the term “Coriolis acceleration” to characterize such a deviation.
Scientists have calculated that this deviation is equal to 2 xsin(A) x B x C, where A is the latitude of the area; IN - angular velocity rotation of the Earth, C – speed of movement of the object. Therefore, at the equator the Coriolis acceleration is zero, and at the poles it has maximum value. IN ordinary life we do not notice this deviation, but in natural processes it turns out to be tangible and long lasting. Those moving with high speed air and water masses. Therefore, for example, some river banks (washed away by water) are steeper, others are flatter. In the northern hemisphere, moving bodies deviate to the right, and in the southern hemisphere, to the left.
4. The revolution of the Earth and the Moon around general center masses and the resulting centrifugal forces, as well as the daily rotation of the Earth around own axis create periodic water levels and subsequent decreases - ebbs and flows (their frequency is approximately twice a day). A tidal wave moves from east to west towards daily rotation Earth. The Earth and Moon complete one revolution around the common center of mass in 27.32 days (lunar month).
