Ask a geography expert! ! Reading skills of sunshine!

The solar illumination map shows how the sun shines on the earth's surface. It can be drawn on the warp and weft network or on the earth's revolution map. The interpretation is comprehensive and has a large span. It is the focus of the first unit of geography in senior high school, and it is also one of the compulsory contents of the college entrance examination.

There are three forms of earth illumination map: polar view, side view and variant map. The way to judge the date on various maps is to observe the length of day and night at various latitudes and the range of day and night at polar regions.

(A) interpretation of polar projection map

1, according to the earth's rotation to determine the north and south poles. The earth's rotation is from west to east, counterclockwise from the North Pole and clockwise from the South Pole, so Figure 1 Figure 2 is the projection of the North Pole center, and Figures 3 and 4 are the projections of the South Pole center.

2. Determine the solar terms according to the tangent between the termination line and the Arctic Circle. If the terminator line is tangent to the Arctic Circle and the Arctic Circle is extremely daytime (as shown in figure 1), or the terminator line is tangent to the Antarctic Circle and it is extremely dark (as shown in figure 5), June 22nd will be the summer solstice in the northern hemisphere. If the terminator line is tangent to the Arctic Circle and is the polar night in the Arctic Circle (as shown in Figure 2), or the terminator line is tangent to the Antarctic Circle and is the polar day in the Antarctic Circle (as shown in Figure 3), it is 65438+February 22nd, that is, the winter solstice in the northern hemisphere. If the termination line coincides with the meridian (as shown in Figure 5), the world is divided equally between day and night, which is March 2 1 or September 23, that is, the vernal equinox or autumnal equinox in the northern hemisphere, and the solar terms in the southern hemisphere are opposite to those in the northern hemisphere.

3. Determine the east-west longitude according to the earth's rotation. Figure 1 Figure 2 The earth rotates counterclockwise, Figure 3, Figure 4 and Figure 5 the earth rotates clockwise. According to the principle that the rotation arrow points to the east, it increases to the east longitude along the rotation direction of the earth based on the 0 meridian, and vice versa. (FB is east longitude, EA is west longitude), longitude indicates north-south direction, and two points on the same meridian are due south and due north. On the projection map with the north pole as the center, any longitude along the center is north, and vice versa. Latitude indicates the east-west direction, with two points on the same latitude being due east and west, due east along the earth's rotation direction, and vice versa (as shown in figure 1-5, point C and point D are located due east of point C).

4. Find the location of the direct point of the sun. According to the date, the latitude position of the direct point of the sun can be determined. In winter to the sun, the direct sunlight point is 23 26' s (as shown in Figures 2 and 3), in summer to the sun, it is 23 26' n (as shown in Figures 1 and 4), and in spring and autumn, it is 0 (as shown in Figure 5). The longitude position is the longitude line 12 when looking for a place, and it is on the meridian in the middle of the daytime hemisphere in the polar map (Figure 1, 2, 3, 4, 5).

5. Calculate the local time. According to the equal division of the four seasons on the equator, it is determined that the sunrise (6 o'clock) is at noon (12 o'clock) and the sunset (18 o'clock) is at midnight (24 o'clock). In figure 1-5, the termination line and the equator intersect at two points AB. Under the influence of the earth's rotation, point B is the time when the sun rises, that is, 6 am, and point A is the time when the sun sets, that is, 18 pm. Point D is right in front of the sun at noon 12, and point C is at 24: 00 midnight (0: 00). For other points, as long as the longitude difference is calculated from the above four points, the time difference can be added and subtracted according to the principle of earth rotation speed 15/ hour and east early (positive) and west late (negative). As shown in figure 1

When the time of point E is the time of point A +45÷ 15/ hour = 18+3=2 1.

The time at point F is the time at point B -45÷ 15/ hour =6-3=3.

(2) Side plan

1, determine the termination line. The terminator line is a big circle perpendicular to the sun's rays, and the dark line of the morning line is a semicircle (as shown in Figures 6 and 7). Because the earth has been rotating from west to east, the semicircle line that jumps from the night hemisphere to the day hemisphere is called the morning line. On the contrary, the semicircle line from the daytime hemisphere to the night hemisphere is the dark line. Facing the side view of the earth's rotation, there is a rule when solving problems: when the sun's rays are on the right side of the picture (as shown in Figure 7), half of the morning and evening circles you see are morning lines, and vice versa (as shown in Figure 6), that is, "left fainting and right morning".

2. To determine the solar terms, the termination line must be perpendicular to the sun rays passing through the center of the earth, and the solar terms can be determined by using the coincidence of the termination line with the earth axis or tangent to the polar circle. If the termination line coincides with the earth axis, cut the termination line into two parts with equal arc of day and night, namely the vernal equinox and the autumnal equinox (as shown in Figure 8). If the terminator line is tangent to the polar circle, it will be extremely day in the north of the Arctic Circle and extremely night in the south of the Antarctic Circle (as shown in Figure 9), which is the summer solstice in the northern hemisphere (June 22). If the terminator line is tangent to the polar circle, the northern part of the Arctic Circle is extremely night, the southern part of the Antarctic Circle is extremely day, and the northern hemisphere is the winter solstice (65438+February 22nd), as shown in Figures 6 and 7.

3. How to calculate the local time? First, calculate the interval between every two meridians. The side view is a hemisphere with a total longitude of 180. With the total longitude 180 ÷ (7- 1) = 30, the time interval between adjacent meridians is calculated as 30 ÷. Then find out at 4 o'clock at noon (12 o'clock) at sunrise (6 o'clock) and at 4 o'clock at midnight (24 o'clock) at sunset (18 o'clock) on the equator to see whether the position is on the east or west side of 4 o'clock, and how many longitudes are separated. According to the principle of east early and west late, we can find out the local time. Example: As shown in Figure 10, when looking for the position of point D, firstly, make sure that point A is sunrise (6 o'clock), point B is noon (12 o'clock) and point C is one of three o'clock at midnight (24 o'clock). Then, when finding the place of point D, the place time of point D is -2× (30 ÷ 15) = 6-4 =.

4. Calculate the length of day and night. According to the longitude of day arc and night arc. As shown in figure 10, when the day length of point A is 90÷ 15/ hour) ×2= 12, and the day length of point D is 150÷ 15/ hour ×2=20. The side view only shows half of the day arc and night arc, so after counting the length of the day arc and night arc on the map, multiply it by 2 to get the day arc and night arc at the required position.

5. The change of solar altitude angle at noon.

Latitude change: the sun's altitude angle at noon at the direct point is 90, which decreases from the direct point to the north and south sides.

Seasonal variation: north of the Tropic of Cancer, it is the largest in summer solstice and the smallest in winter solstice; In the south of Capricorn, the winter solstice is the largest and the summer solstice is the smallest. Between the Tropic of Cancer and the Tropic of Cancer, there is direct sunlight twice a year, and the height angle of the sun is the largest at noon. For a certain place, when the direct point of the sun moves close to the point, the height of the sun rises gradually at noon, and vice versa.