Section 1: The Rotational Motion of the Earth
First, the three elements of rotational motion
1. Rotation direction: from west to east; pole top view): south and north reverse.
(1) Side view: from west to east.
(2) Look down
2. Rotation period: Stellar day (23 hours, 56 minutes and 4 seconds, true period)
Solar day (24 hours, day-night cycle)
3. Rotation speed: angular velocity: (1) no velocity at the pole; (2) global equality of angular velocity = 15 ° / hour;
Linear velocity: (latitude factor) Linear velocity is the largest at the equator, decreasing from the equator to the poles;
The southern and northern hemispheres have the same number of latitudes and the same site line speed: 40 ° N line speed = 40 ° S line speed.
The linear velocity at 60° north and south latitudes is about half of that of the equator: 0° N linear velocity = 60 ° N \ S linear velocity.
The linear velocity of the north and south poles is zero: 90 ° linear velocity = 0.
(Altitude factor) The higher the altitude, the greater the linear velocity.
【Extension 1】 The relationship between the speed of geostationary satellites and the rotation speed of the Earth:
The angular velocity is the same; the linear velocity of the synchronous satellite is greater than the speed of the Earth's rotational line
Second, the geographical significance of the rotation of the earth
(1) Day and night turnover and morning and evening lines
1.Day and night replacement
Diurnal phenomena: properties of the earth itself (non-luminous, opaque);
Day and night turnover: The phenomenon of day and night combined with the rotation of the earth.
2. Distribution characteristics and judgment of morning and evening lines
Morning and evening lines often appear in light maps, and are easily confused when mixed with numerous longitude and latitude lines. The core of interpreting the light map is to quickly interpret the morning and evening lines. The distribution of the graticule is fixed, and the morning and evening lines divide day and night. It is also easy to interpret. The problem is that the graphics are diverse.
(1) Distribution characteristics of morning and evening lines
(1) The morning and evening lines are a large circle that divides the Earth equally.
(2) The plane where the morning and dusk lines are located is always perpendicular to the sun's rays, and the morning and dusk lines on the Earth's sphere are perpendicular and tangent to the sun's rays. The solar altitude angle on the morning and evening lines is 0°.
(3) The morning and evening lines divide the equator equally. The intersection of the morning line and the equator is 6:00 at the time, and the intersection of the dusk line and the equator is 18:00.
(4) The angle of change between the morning and evening line and the meridian is 0 ° -23 ° 26 ', the spring equinox day and the autumn equinox day coincide with the warp coil, and the angle between the morning and evening line and the meridian line is 23 ° 26 '. It can also be said that the angle between the morning and evening lines and the meridian coil is the latitude of the direct point of the sun. This is shown in the following figure. (α＝β)
(5) The morning and evening lines are only tangent to the polar circle on the second to the second day. The cut-out is at 0:00 (24:00) or 12:00.
(6) The morning and evening line moves at a speed of 15 ° / h from east to west, which is contrary to the direction of the Earth's rotation.
（2）． Types of morning and evening lines
(1) Straight type
(2) Arc type
(3) Judgment of the morning and evening lines
On the basis of clarifying the direction of the Earth's rotation:
Following the direction of the Earth's rotation, it is the morning line that enters the day hemisphere from the night hemisphere; the dim line from the day hemisphere into the night hemisphere.
3. The application of morning and dusk lines in light maps: (the use of two tangent points, two intersection points)
(1) Determine the direction of rotation of the Earth
(2) When determining the place
(1) 6 o'clock at the place on the meridian that passes through the intersection of the equator and the morning line, and 18 o'clock at the place on the meridian that passes through the intersection of the equator and the dusk line.
(2) The place on the meridian where the direct sun is located is 12 noon, and the place on the meridian line that forms the meridian opposite it is 0 hours (or 24 hours).
(3) When passing the longitude line where the morning and evening lines and the weft coil are tangent, it is either 0 o'clock (or 24 o'clock) or 12 o'clock. The polar day phenomenon near the tangent point is 0 o'clock (or 24 o'clock), and the polar night phenomenon near the tangent point is 12 o'clock.
(3) Determine the date and season
(1) The morning and evening lines pass through the north and south poles, coincide with a certain warp coil, and intersect perpendicularly with all the weft coils, and this day can be determined to be the day of the vernal equinox or the day of the autumn equinox.
(2) The morning and dusk lines are tangent to the Arctic circle, and the polar day phenomenon occurs in the Arctic Circle and its north, and it can be determined that this day is the day of the summer solstice.
(3) The morning and dusk lines are tangent to the Arctic circle, and the polar night phenomenon occurs in the Arctic Circle and its north, and it can be determined that this day is the winter solstice day.
(4) Determine the position of the direct sun point
The longitude of the meridians of the bisecrated day hemisphere on the insolation chart is the longitude of the sun's direct point. The latitude of the sun's direct point needs to be determined according to the latitude of the parallel tangent to the morning and dusk lines, if the latitude of the parallel tangent to the morning and dusk lines is α, the latitude of the sun's direct point is equal to 90°-α (note: the direct sun point must be in the same hemisphere as the area where the polar day phenomenon occurs).
(5) Determine the length of day and night
The length of the day in a place is equal to the number of times spanned by the day arc between the latitude coil and the intersection of the morning and evening lines; the length of the night is equal to the number of times spanned by the night arc on the latitude coil where the place is located.
(6) Determine the sunrise and sunset time
The sunrise time of a place is the time at the intersection of the meridian and the morning line in the place; the sunset time is the time at the intersection of the meridian and the dusk line where the place is located. The calculation formula for sunset and sunrise time in a certain place is 12± day length/2.
(7) Determine the range of polar days and polar nights
The morning and evening lines are tangent to which the weft coil is, and the polar day or polar night phenomenon occurs in the latitude range between the latitude coil and the pole. The polar day and night phenomena in the northern and southern hemispheres are just the opposite.
(2) Time zone, zone time and date range
1. Local time, each place has its own time, called local time.
The longitude varies from region to region, and the longitude is replaced by the longitude. Places on the same meridian are the same, and longitudes are different, then places are different.
We see the sun first, because the earth rotates from west to east, and the sun is seen first in the east, that is, the time is relatively early, and the number of times is relatively large.
When there are countless meridians on the earth, there will be countless places, and in order to unify time, the earth is divided into time zones.
2. Time Zone: Indicates a region with a longitude span of 15°, with a total of 24 time zones around the world.
Calculate the time zone of a place: Put its longitude at 15, look at the remainder. If the remainder is less than 7.5, the quotient is the time zone in which the place is located. If the remainder is greater than 7.5, the quotient +1 is the time zone of the place.
3. Zone time: Time when the central meridian of the time zone is at the place. A time that is used together as an entire time zone.
【Direction of the question】 For the calculation of local time and time zone, it is known that a certain place and a certain time, when is it to seek a certain place?
【Steps to solve the problem】
(1) Find out the longitude of the two places, and distribute the pattern of the east longitude degree on the east side and the west longitude degree on the west side.
(2) Calculate the time difference according to the longitude difference: 15 ° = 1h, 1 ° = 4min
(3) East Plus West Minus.
Note: (1) If the calculated result exceeds 24, it indicates that a day newer than the known date given by the material has occurred. If the calculation is negative, it means that it is one day slower than the known date given by the material, that is, yesterday.
(2) There is also a question type that seeks where at a certain time, and also finds the unknown according to the known. The solution step is to put the large time in the east and the small time in the west (east early and west late). The schedule difference is then calculated based on the time difference. East plus West Minus.
4. Changes in dates on Earth and judgment of scope
(1) Distribution of old and new days:
Two solar lines on Earth: the meridian at 0 o'clock (natural, changing);
International diurnal line (fixed, roughly coinciding with the 180° meridian).
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Old day
The topic is to draw two daily lines directly, 180° on the far right, and the meridian at 0 o'clock on the left.
At 0 o'clock the meridian is east to 180° for the new day, and west to 180° for the old day.
To judge the date of a place, that is, to determine whether it is on a new day or an old day, the key is to determine whether the longitude of the place is on the east side of the meridian at 0 hours (new day) or on the west side (old day).
(2) The range of old and new days
【Solution 1】: The key to judging the date range is to find the meridian where 0 is located. The range from the 0 point meridian east to the 180° meridian is the new day range, and the range between the 0 hour meridian west and the 180° meridian is the old day. If the 0 hour meridian and the 0° meridian coincide, the old and new are half, and if the 0 hour meridian and the 180° meridian coincide, the world is a date.
【Solution 2】If the question directly asks the new (or old) proportion of the range of the day, it is enough to directly calculate the place of 180 ° meridian.
What time is it when the 180° meridian is at, and the time it takes to enter the area of the new day is a few hours; because the new day begins at 180°.
The known time given to find out in the figure is calculated from the eastward to 180° to calculate the time of the 180° meridian.
In turn, the time it takes for the world to enter the area of the new day is a few hours, and the time it takes to enter the area of 180° longitude is what time.
(3) Geodesic deflection forces and their geographical significance
1. Definition: Due to the rotation of the earth, the movement of an object that is in horizontal motion on the surface of the earth deviates from the original direction of motion.
2. Law: The northern hemisphere is biased to the right, the southern hemisphere is deflected to the left, and the equator is not biased
3. Features: The ground deflection force is perpendicular to the direction of movement of the object; it only affects the direction of motion, does not affect the speed of movement; the higher the latitude, the greater the geodesic deflection force.
4. Geographical significance: (1) The location of human activities along the river is affected by the geodestropic bias force, and the rivers in the northern hemisphere erode the right bank and silt up on the left bank, so the port and flood control embankment are generally built on the right bank, and the settlement and sand dredging site should be selected on the left bank. The specific illustrations are as follows:
(2) The firing of shells and the determination of the airdrop orientation of the items.
(3) According to the weather data map, correctly judge the wind direction and its changes.
(4) Judge the northern and southern hemispheres according to the deflection direction of wind or water currents.
Section 2 The Movement of the Earth - Rotation
The rotational motion of the Earth from a macroscopic point of view is the movement of the Earth around the sun in the plane of the ecliptic from west to east.
First, the characteristics of the earth's rotational movement:
1. Direction: from west to east. From above the North Pole, it is counterclockwise; from above the South Pole, it is clockwise.
2. Orbit (ecliptic plane): An ellipse that approximates a perfect circle.
3. Period: One stellar year, 365 days, 6 hours, 9 minutes and 10 seconds.
4. Speed: Perihelion is the fastest, aphelion is the slowest.
5. Yellow-red angle
The yellow-red angle is the angle between the ecliptic plane and the equatorial plane, which is currently 23° 26′.
Due to the existence of the yellow-red angle, the direct point of the Earth in the process of orbiting the Sun is constantly moving.
Note: If the yellow red angle becomes 0°, the direct solar point is always located on the equator, the position of the air pressure belt and wind belt on the earth will not move, the annual change of the noon sun height and the length of day and night will disappear, and the four seasons and five belts on the earth will also disappear.
From a microscopic point of view, the rotational motion of the Earth is the process of the return movement of the sun's direct point of view between the Tropic of Cancer of the Earth.
Causes the direct sun to move back and forth between the Tropic of Cancer.
(1) Thinking process
(2) Specific analysis (effects of changes in yellow-red angles)
Second, the geographical significance of the earth's rotation
Changes in the global length of day and night and the angle of solar altitude at noon should be analyzed dynamically (movement of direct points).
(1) Changes in the length of day and night
1. Illumination map interpretation
In the light map, the length of day and night is mainly judged by the light map.
The morning and evening lines are determined by the sun's rays and are vertically related.
Annual motion of the sun's direct point: Moves back and forth between the Tropic of Cancer with the point of direct light. Thus, the morning and evening lines swing back and forth in the range from pole to pole.
The direct point of the sun moves, the morning and evening lines are deflected, and the tangents are in different latitude coils (which are more than the degrees of the direct point), and the length of day and night changes around the world.
Note: Sometimes the latitude of the point of direct illumination is also reflected.
2. Specific date interpretation (direct solar point regression motion chart):
The direct point of the sun moves between the tropic lines for a year, and the latitude at which a certain date can be deduced from four fixed points from two-seconds to four fixed points of the day. The Sun travels roughly 8 latitudes a month.
Knowing the hemisphere where the direct point of fire is located, you can know the length of day and night in a certain place. And if you want to know the change of day and night in a certain place, you also need to know which hemisphere the direct shooting point is moving.
3. The time of sunrise and sunset is estimated to calculate the length of day and night:
Sunrise and sunset time and length of day and night: day length = sunset - sunrise.
[Thinking Expansion 1]: The size of the day-night difference
Different regions: the equator is always divided between day and night, the day and night difference is 0, and the higher the latitude, the greater the difference between day and night length.
Different seasons: the smallest two-minute day, the largest two to the day.
[Thinking Expansion 2]: The length of day and night is about the symmetry of dates
Find two dates of equal length of day and night in a certain place (non-polar region, and pay attention to its hemisphere): if it is the date range of the summer half year (3.21- 9.23), then the date of the summer solstice day (June 22) is symmetrical;
If it is the date range of the winter half year (9.23 - 3.21 of the following year), then the date of the winter solstice day (December 22) is symmetrical if;
If the length of day and night in a certain place is just opposite, it is symmetrical to the date of the quarter day.
【Thinking Expansion 3】The length of day and night is about the symmetry of latitude
At the same latitude and on the same date, the length of day and night in the northern and southern hemispheres is just the opposite.
(5) Calculation of the length of day and night
1. Calculate the arc of the circadian arc using the arc of the day and night
Day (night) length = day (night) arc / 15°
2． Calculated using sunrise and sunset times
(1) Basis:
(1) Daytime: Sunrise and sunset time symmetrical about 12 noon.
(2) Nighttime: Sunrise and sunset time symmetry about 0 o'clock.
(3) Morning time = afternoon time.
(4) The length of the first half of the night = the length of the second half of the night.
As shown in the following figure:
(2) Calculation method:
(1) Long day time = sunset time - sunrise time = 2× (12 - sunrise time) = 2 × (sunset time - 12) = 24 - night length
(2) Sunrise time = 12 - day length / 2 = half of the night length
3． It is calculated using the distribution law of the length of day and night
(1) The day and night conditions, sunrise and sunset times are the same at each point on the same parallel.
(2) Two parallel lines with the same number of latitudes in the southern and northern hemispheres have equal day and night duration, that is:
The length of the day (night) in a place in the southern hemisphere = the length of the night (day) in a certain place in the same latitude in the northern hemisphere
4． Utilizes the symmetry of the date calculation
(1) Regarding two times of two-day symmetry, such as point A and point B, the direct point of the sun is located in the same position.
(2) Regarding the two times of dichotomy, such as B point and C point, the direct point of the sun is located in different hemispheres, but the number of latitudes is the same.
(2) Changes in the altitude angle of the sun at noon
1. Noon sun altitude angle
Solar Altitude Angle: The angle formed between the sun's rays and the ground, the maximum solar altitude is at 12 noon in the middle of the day.
The noonday sun altitude angle is determined by the latitude at which the direct point is located, and the closer to the direct point, the greater the noonday sun altitude angle.
2. Distribution of the altitude angle of the noon sun
The angle of the noon sun altitude is determined by the latitude at which the direct point of light is located,
3. Change of altitude angle of the sun at noon:
The change in the altitude angle of the noon sun is related to the movement of the direct point of light.
【Latitude change】
Spring and autumn equinoxes: directly at the equator, the noon sun altitude angle from the equator to the north and south poles decreased.
Summer Solstice Day: The direct point of direct fire is directly on the Tropic of Cancer, and the area north of the Tropic of Cancer and its area reaches the maximum of the year.
The northern hemisphere latitudes reach the minimum of the year;
Winter Solstice Day: The direct point of direct fire is directly at the Tropic of Cancer, and the area south of the Tropic of Cancer and the area south of it reaches the maximum of the year.
The latitudes of the Southern Hemisphere reach the minimum of the year.
The height of the noonday sun decreases from the latitude of the direct sun to the north and south.
(1) Summer solstice day: The height of the noon sun decreases from the Tropic of Cancer to the north and south sides, as shown by the c-fold line in the figure.
(2) Winter solstice day: The height of the noon sun decreases from the Tropic of Cancer to the north and south sides, as shown by the a-fold line in the figure.
(3) Spring and autumn equinox days: The height of the noonday sun decreases from the equator to the north and south sides, as shown by the b-fold line in the figure.
【Annual change】
(1) Between regression lines:
The maximum height of the noonday sun is 90°, and there are two direct solar rays every year, that is, two noon sun height maximums in a year.
(2) On the tropic line:
The maximum height of the noon sun is 90°, and there is only one direct solar ray in a year, that is, only one noon sun height maximum in a year.
(3) The regression line is between the extreme points
The maximum height of the noon sun is 90°, and there is only one direct solar ray in a year, that is, only one noon sun height maximum in a year
[Extension 1]: Directions of sunrise and sunset.
[Extension 2]: Sun Sunday vision movement.
In the examinations of the past years, the area between the tropic line and the polar circle is mainly examined, focusing on the changes in the solar trajectory in the region.
【The key to solving the problem】Three-point fixed trajectory, sunrise and sunset orientation + noon sun position.
The sunrise and sunset orientation can be determined according to the date of the hemisphere where the direct point of direct sunlight is located, and the key lies in the position of the noonday sun.
For the Earth north of the Tropic of Cancer, the sun is always in the south. Therefore, its trajectory is:
[Northern Hemisphere Summer Half Year] [Northern Hemisphere Winter Half Year]
For the Earth south of the Tropic of Cancer, the sun is always in the north. Therefore, its trajectory is:
【2/2】
[Extension 3]: Changes in the orientation and length of the shadow
(1) The orientation of the shadow: opposite to the direction of the sun. First determine the position of the sun at this time to infer the direction of the shadow. Similarly, the orientation of the shadow can also reverse the position of the sun.
(2) Changes in the length of the shadow:
In the middle of the day: the highest noon sun, the shortest shadow length, then the sunrise → noon, the shadow length shortened; noon → sunset, the shadow length becomes longer.
Of the year: (closer to the sun) The greater the angle of the sun's altitude at noon, the shorter the shadow. (The higher the latitude, the longer the shadow at noon)
4. Use of the noonday sun altitude angle:
(1) Calculation of the altitude angle of the noon sun: H = 90 ° - latitude difference
illustrate:
(1) "Two points" means the place sought and the point of direct sunlight.
(2) The calculation of the latitude difference between two points follows the principle of "same subtraction and different addition", that is, if two points are in the northern (southern) hemisphere, the latitude of two points is "large number reduction"; two points belong to different hemispheres in the north and south, and the latitudes of the two points are added.
When the sun is directly at point B (10°N):
Point A (40°N) noon sun altitude:
H = 90 ° - AB latitude difference = 90 ° - (40 ° - 10 °) = 60 °.
C-spot (23°26′S) noon solar altitude:
H = 90 ° - BC latitude difference = 90 ° - (10 ° + 23 ° 26 ') = 56 ° 34 '.
(2) Determine the orientation of the house
For more abundant sunlight, in areas north of the Tropic of Cancer, the noonday sun is located in the south and the houses face south; in the areas south of the Tropic of Cancer, the noonday sun is located in the north and the houses face north.
In order to get the most sunlight, the orientation of the houses everywhere is related to the location of the noonday sun.
(1) The area north of the Tropic of Cancer, where the noonday sun is located in the south, and the houses face south.
(2) The area south of the Tropic of Cancer, where the noonday sun is located in the north and the houses face north.
(3) Determine the distance and height of the building
In order to better ensure that each floor has good lighting, the floor should maintain an appropriate distance from the building. In general, the distance between buildings is small in areas with lower latitudes, and larger distances in areas with higher latitudes. Taking China as an example, see the figure below, the height of the south building is h, and the height of the noonday sun on the winter solstice day is H, then the minimum floor spacing L is: L=hcotH.
(4) Adjustment of the inclination angle of the solar water heater
To calculate the angle at which a solar panel is placed in a certain place, it is necessary to know the angle of the noonday solar altitude in that place.
Combined with the latitude of the place, the conclusion is used:
。
Sixth, the comprehensive interpretation of the illumination map
Earth illumination maps often borrow the distribution of day and night at a certain time, rely on the organic combination of some special points, lines, surfaces and other elements, comprehensively examine the geographical significance of the earth's movement, and use this to judge the seasons, calculate the time, analyze the length of day and night and the change characteristics of the noon sun height.
[Common Illustrations]
Interpretation method
1． Distinguish the day and night hemispheres and determine the morning and evening lines
(1) Morning line: rotate along the earth into the day hemisphere, with the night hemisphere to the west and the day hemisphere to the east.
(2) Dim line: rotate along the earth into the night hemisphere, with the western hemisphere as the day hemisphere and the east as the night hemisphere.
2． Determines the direction of the Earth's rotation
(1) Judging according to the direction of the Earth's rotation: the sky above the North Pole is counterclockwise, and the sky above the South Pole is clockwise.
(2) Judging according to the morning and evening line:
Note: (1) If the figure is the dusk line and the morning line, the earth rotates counterclockwise, and the center is the North Pole;
(2) If it is the morning line and the dusk line, the earth rotates clockwise and the center is the south pole.
3． Determines the location of the sun's direct point
(1) Determine the longitude:
(1) The meridian is 12 when the place is found according to the known meridian in the light map.
(2) From the light map, the meridian of the bisected diurnal hemisphere can be intuitively seen.
(2) Determine the latitude:
It is determined according to the latitude of the parallel tangent to the morning and evening lines. The latitude of the direct point is redundant with the latitude of the line. If the latitude of the parallel tangent to the morning and dusk lines is α, the latitude of the direct sun's point is 90°-α.
4． Determine the date and season
(1) Use the length of day and night in the northern hemisphere: if the day is long and the night is short or there is a polar day phenomenon near the North Pole, it is the summer half year of the northern hemisphere, and vice versa, it is the winter half year; if the day and night are equally long, it is the vernal equinox day or the autumn equinox day.
(2) Determination of special dates:
(1) The morning and evening lines coincide with the meridians (or the morning and dusk lines pass through the poles), around March 21 or September 23.
(2) The morning and evening lines are tangent from the polar circle, and if it is night in the Arctic Circle, it is around December 22, and if it is day, it is around June 22.
(3) According to the oblique relationship between the morning and evening lines and the meridians.
5． Determine sunrise and sunset
(1) Determination time:
(1) The sunrise rises at the same time everywhere on the morning line, and the sunset sets at the same time everywhere on the dusk line.
(2) When the place where the meridian and the morning line intersect, it is the sunrise place of the place; when the place where the longitude line and the dusk line intersect is the sunset place of the place.
(2) Determine the direction:
(1) When the sun directly hits the equator, that is, the spring and autumn equinox days, all over the world (except for the poles), the sunrise is due east and the sunset is due west.
(2) When the direct solar point is located in the northern hemisphere, all over the world (except for the polar day and night areas), the sunrise is northeast and the sunset is northwest.
(3) When the direct solar point is located in the southern hemisphere, all over the world (except for the polar day and night areas), the sunrise is southeast and the sunset is southwest.
(4) Where the polar day appears, the northern hemisphere rises north and falls due north; the southern hemisphere rises south and falls south.
6． When determining the place
(1) 6 o'clock at the place on the meridian that passes through the intersection of the equator and the morning line, and 18 o'clock at the place on the meridian that passes through the intersection of the equator and the dusk line.
(2) The place on the meridian where the direct sun is located is 12 noon, and the place on the meridian line that forms the meridian opposite it is 0 hours (or 24 hours).
(3) When passing the longitude line where the morning and evening lines and the weft coil are tangent, it is either 0 o'clock or 12 o'clock. The polar day phenomenon near the tangent point is 0 o'clock, and the polar night phenomenon near the tangent point is 12 o'clock.
7． Determine the length of day and night
(1) Determine the length of the day and night:
In the light map, the morning and dusk lines divide the latitude line of the earth into two parts: the day arc and the night arc, and the day length is equal to the number of times the day arc of the latitude line spans, and the night length is equal to the number of times spanned by the night arc of the latitude line.
(2) Determine the length of day and night:
The day arc (or night arc) of each place on the same parallel is of equal length, if the day arc is greater than the night arc, the day is long and the night is short, and if the day arc is smaller than the night arc, the day is short and the night is long.
(3) Determine the polar day and night range:
The morning and evening lines are tangent to which of the weft coils, and the polar day or polar night phenomenon will occur in the latitude range between the latitude coil and the pole, and the polar day and polar night phenomenon in the northern and southern hemispheres will occur at the opposite time.
8． Determine the height of the midday sun
The sun's direct latitude is 90° at the height of the noonday sun, and the height of the noonday sun in other places decreases from this parallel to the north and south.
Seven, four seasons and five belts
1． The four seasons change
(1) The origin of the four seasons: the length of day and night and the height of the noonday sun change with the change of the season.
(2) Division of the four seasons
(2) The four seasons of many countries in the northern temperate zone: March, April, and May are spring, and so on, every three months is a season.
2． Division of the five belts
(1) Causes of the five belts: the length of day and night and the height of the noon sun change with the change of latitude in a year.
(2) Five belt divisions