Draw side views of the vernal equinox, summer solstice, autumn solstice and winter solstice.
Interpretation skills of illumination map
1, judging the northern and southern hemispheres
The meridian in side view is usually an arc, connecting the north and south poles, usually upper north and lower south; In the top view, the longitude lines are radially distributed with the pole as the center and the latitude lines are concentric circles, which can usually be judged according to the rotation direction of the earth. Counterclockwise is the northern hemisphere, clockwise is the southern hemisphere. It can also be judged by the longitude change that the direction along the east longitude becomes larger and the west longitude becomes smaller is the direction of rotation. As shown in figure 1, the direction of increasing east longitude is taken as the rotation direction, and figure 1 is clockwise rotation, which is a top view of the southern hemisphere.
2. Determine the termination line
The terminator line is the dividing line between the day and night hemispheres. It has two remarkable characteristics: one is that the terminator line is always perpendicular to the sun's rays, and the other is that it always bisects the equator. The key to judging the terminator line is to look along the rotation direction. The morning line is from night to day, and the dark line is from day to night. The morning line and the dark line form a big circle to divide the earth equally. In dichotomy, the termination line coincides with the warp circle, and the rest of the time intersects with the warp. As shown in figure 1, arc AD is the morning line and arc BD is the faint line; The CD in fig. 2 is an early line; The arc NAS in fig. 3 is the morning line.
3. Determine the coordinates of the direct point of the sun.
Because sunlight is parallel light and the earth is a sphere, at a certain moment, the sun only shines on a certain point on the earth, which is the direct point of the sun and located in the center of the hemisphere during the day. At the point of direct sunlight, when the height of the sun is 90 at noon and the meridian is12, the shadow length of the object at the point of direct sunlight is zero. The latitude position of the direct point of the sun can be judged according to the position of the termination line. If the termination line is tangent to the polar circle, and all the days are in the Arctic circle and all the nights are in the Antarctic circle, the sun will directly hit the Tropic of Cancer; If the arctic circle is full of polar nights and the Antarctic circle is full of polar days, then the tropic of Capricorn points directly to it; If the dark line coincides with the meridian, it points to the equator. As shown in figure 1, point F is the direct sunlight point with the coordinate of (23 26' s, 90 E), in figure 2, the direct sunlight point is F, and in figure 3, the termination line coincides with the meridian, so the sun should face the equator, and the direct sunlight point is B with the coordinate of (0, 30 E).
4. Judge the length of day and night and the time of sunrise and sunset.
The terminator line divides the latitude of the earth into two parts: day arc and night arc. The length of solar arc and night arc determines the length of day and night, and the radian of 15 is 1 hour. At the same latitude, the length of day and night is the same, and the time of sunrise and sunset is the same. The intersection of the morning line and latitude in a place is the sunrise time, and the intersection of the dark line and latitude is the sunset time. In spring and autumn, the length of day and night on earth is equal, with sunrise at 6 o'clock and sunset at 18 o'clock; The equator is equally divided day and night throughout the year, rising at 6 o'clock and setting at 18 o'clock; At other times, except the equator, the length of day and night is different at all latitudes, and the time of sunrise and sunset is also different. When the sun shines directly into the northern hemisphere, the days are long and the nights are short in all parts of the northern hemisphere, and the days are longer as you go north. The extreme sunrise appears in the North Pole, and the range of extreme days is north of the north latitude (90-the latitude where the sun shines directly). In the southern hemisphere, the days get shorter and the nights get longer. The farther south, the longer the nights get. The polar night appears in the South Pole, and the range of the polar night is south of the south latitude (90-the latitude where the direct sun point is located). When the sun shines directly into the southern hemisphere, the situation is just the opposite. The latitude of the direct point of the sun and the latitude range of extreme day and night are complementary. The length of day and night is usually judged by calculating the longitude difference. The length of a day can be obtained by multiplying the longitude of the solar arc somewhere by 4 minutes. It should be noted that half of the solar arc can usually be seen in the side view, and the other half should be taken into account. Generally speaking, the longitude is equal, and 30,45, 15 is a grid, which is convenient to calculate. After getting the length of day, we can adopt noon 12- length of day /2= sunrise time, 12+ length of day /2= sunset time. As shown in Figure 2, the day and night length of point E is 12, the sunrise is 6: 00, and the sunset is 18. In Figure 2, point A is just on the morning line, with the sunrise at 4: 00 and the sunset at 20: 00, and the day length is 16 hours. You can also get the day length 16 hours by multiplying 2 by 4 minutes according to the longitude of the solar arc span where A is located.
5. Judge the height of the sun at noon
The difference between the height of the sun at noon and the height of the sun: the height of the sun refers to the angle between the sun and the ground level, and the height of the sun changes constantly with the rise and fall of the sun in a day; The midday sun height refers to the sun height 12 when the sun height is maximum in a day. The direct point of the sun; The height of the sun at noon is 90; And other fields; The height of the sun at noon can be calculated according to H = 90, which is the latitude between the required latitude and the direct point. At noon at the same latitude, the height angle of the sun is the same; The distribution law of noon sun height is decreasing from the latitude of the direct point to the north and south, and the closer to the latitude of the direct point, the greater the noon sun height angle. As shown in figure 1, the noon sun height at point f is 90, and the noon sun height at point b is 90-23 26' = 66 34'; The noon sun height at point C is 90-(66 34'-23 26') = 46 52'.
Step 6 judge the season and date
Judging the season according to the position of the termination line and the direct point of the sun, the intersection point of the termination line coincides with the meridian on the vernal equinox, and intersects with the meridian at other times; From the second solstice to the third, the termination line is tangent to the polar circle, but it is oblique at other times. The point of direct sunlight in the northern hemisphere is summer half year, while in the southern hemisphere it is winter half year. There are usually two kinds of date distributions on the earth, and their boundaries are: 180 international date line and meridian at 24 o'clock or 0 o'clock local time; When there is only one date on the earth, the meridian of 180 is the meridian of 0 or 24 o'clock; When the two dates of the earth are equally divided, the local time of meridian 180 is 12 hours. As shown in figure 3, the sun shines directly at the equator, which is the vernal equinox in spring and autumn. The two meridians 180 and 150 W in the figure are the dividing lines of the two dates.