< h1 class="pgc-h-center-line" > knowledge points</h1>
1. According to the morning and dusk line, judge the direct sun shooting point
The dividing line between day and night on Earth is called the "morning and evening line" ( ) . The direction of the earth's rotation is from west to east, and in the direction of rotation, the dividing line from night to day is called the morning line; the dividing line from day to night is called the dusk line. According to the morning and evening lines, the latitude and longitude of the time, season and direct sun point can be judged:
(1) Judgment time. The intersection of the morning line and the equator is 6:00 a.m., the intersection of the dusk line and the equator is 18:00 p.m., the central meridian of the night hemisphere is 0:00, and the central meridian of the day hemisphere is 12:00 noon;
(2) Judging the season. a) The summer solstice is when the morning and evening lines intersect the Arctic Circle and the North Arctic Circle has been in the diurnal hemisphere; if the North Arctic Circle has been in the night hemisphere, it is the winter solstice; b) the morning and dusk lines intersect with the North Pole, the vernal or autumn equinox;
(3) Judge the latitude and longitude of the sun's direct point. a) The central meridian of the day hemisphere, that is, the longitude of the direct solar point; b) the latitude of the direct solar point = 90 ° - the northernmost latitude of the morning and dusk circle, for example, the northernmost point of the morning and dusk circle is 66 ° 34 ′N (Arctic Circle), then the latitude of the direct point of the sun at this time is 23 ° 26 ′N.
Fig. 1 According to the morning and dusk line, the direct sun point is judged
2. Midday solar altitude angle
The noonday solar altitude angle refers to the angle between the sun's rays and the ground plane at 12:00 local time (α in the image below). The calculation formula for the angle of the noon sun altitude is as follows:
α = 90° - | b - c |
Where the α is the noon sun altitude angle, the β is the latitude of the observer, and the γ is the latitude of the direct sun. The smaller the latitude difference between the observer (β) and the direct sun (γ), the greater the sun's altitude angle.
Note: When the observer is in the same hemisphere as the direct sun, |β-γ| subtraction; when located in different hemispheres, use addition. For example, in the same hemisphere, 40°N-23°26′N=16°34′; in different hemispheres, 40°N-23°26′S=40°+23°26′=63°26′.
Fig. 2 Schematic diagram of the solar altitude angle
< h1 class="pgc-h-center-line" > example question</h1>
Figure 3 Example question
Answer: A, D
Intensive analysis: (1) Analyze the position of the direct sun. (1) In the figure, there is a top view of the Earth (a little sideways), the upper center position is the north pole, the bottom circle of latitude is the equator, the dark shadow represents the night hemisphere, and the light shadow (white) represents the day hemisphere. The dividing line of the day and night hemisphere is the morning and evening line, and the morning and dusk line passes through the North Pole, so at this time the global day and night are equal in length, which is the vernal equinox or autumn equinox, and the sun directly hits the equator (0 °) ;(2) The meridian in the center of the day hemisphere is the meridian of the direct sun. As can be seen from the figure, the meridian in the center of the day hemisphere is located on the right side of C, and (3) the meridian on the left side of C passes through the United Kingdom and the Gulf of Guinea in Africa, so it is 0°. At this time, the day and night are equally divided, and the day hemisphere occupies 180° longitude and is divided into 6 parts, so the two adjacent meridians are spaced by 30°. Therefore, at this time, the meridian on the right side of the C ground is 30 ° E. Therefore, the position of the direct point of the sun at this time is (0 °, 30 ° E).
(2) Calculate the angle of the noon sun altitude. (1) Noonday sun altitude angle = 90 ° - | local latitude - the sun direct point latitude |, the sun direct point latitude is 0 °, so the noon sun height angle = 90 ° - local latitude, that is, the smaller the local latitude (closer to the equator), the greater the noon sun height angle; (2) As can be seen from the map, A is the closest to the equator and the lowest latitude, so the noon sun altitude angle of A is the largest.
(3) Analyze the direction of the sun. (1) When analyzing the position of the sun seen by the observer, the position of the direct point of the sun cannot be used, but the apparent trajectory of the sun should be used; (2) the central meridian of the day hemisphere at this time is 12:00 noon, that is, A and B are in the morning, C is noon, and D is in the afternoon; (3) At this time, it is the vernal equinox or autumn equinox, so the sun rises in the east and sets in the west, and the trajectory of the movement is south, that is, at sunrise to noon, the sun is located in the southeast, the sun is located in the south at noon, and the sun is in the southwest when noon to sunset. Therefore, at this time, the sun observed in A and B is located in the southeast, C is located in the south (a little east), and the Ding is located in the southwest.
< h1 class="pgc-h-center-line" > summary</h1>
The apparent trajectory of the Sun
The solution ideas of the example problems in this section are: (1) judging the season according to the position of the morning and evening line, and then judging the latitude of the sun's direct point; (2) finding the longitude of the sun's direct point according to the longitude range of the day hemisphere; (3) judging the solar altitude angle in various places according to the latitude and longitude of the sun's direct point; (4) judging the sun's position according to the sun's apparent trajectory.
The solar apparent motion trajectory can determine the direction of sunrise and sunset and the direction of the sun, which is mainly related to the position and observation time of the viewer:
(1) The position of the observer
(1) Located in the northern hemisphere, the apparent trajectory of the sun tilts southward, and the noonday sun is located in due south;
(2) Located in the southern hemisphere, the apparent trajectory of the sun is tilted to the north, and the noonday sun is located in the north;
(3) Located at the equator, the apparent trajectory of the sun is not tilted, and the noon sun is directly above.
(2) The date of observation
(1) Spring equinox ~ autumn equinox, the sun rises in the northeast and sets in the northwest, that is, the northeast sunrise and the northwest sunset;
(2) From the autumn equinox to the spring equinox of the following year, the sun rises in the southeast and sets in the southwest, that is, the southeast sunrise and the southwest sunset;
(3) Spring equinox and autumn equinox, the sun rises in the east and sets in the west, that is, the sunrise in the east and the sunset in the west.
(3) Time of observation (assuming northern hemisphere, vernal equinox)
(1) At 6:00 in the morning, just after sunrise, the sun is located due east;
(2) From 6:00 a.m. to 12:00 a.m., the sun moves from due east to due south, that is, the sun is located in the southeast;
(3) At 12:00 noon, at noon, the sun is located due south;
(4) From 12:00 to 18:00 in the afternoon, the sun moves from due south to due west, that is, the sun is located in the southwest;
(4) At 18:00 in the evening, just before sunset, the sun is located in the west.
Figure 4 The apparent trajectory of the Sun
[Every night at 20:00, one question per day, learn geography well]