Why is it said that the longitude difference between the morning line and the dusk line is 15 degree

If the morning and dusk lines and the equator intersectWarpThe longitude is , then the longitude of the direct point of the sun is equal to 90° (the morning line is added to the east, and the evening line is subtracted to the west, i.e. the morning line is " " and the evening line is " ".

If the morning and dusk line with a certain oneWeftThe longitude of the tangent point, then the longitude of the point where the sun is directly exposed is equal to or 180°

1. There are two intersections between the morning and dusk lines and the equator, and the places where these two points are located are always 6 o'clock and 18 o'clock. The morning line (day in the east and night in the west) and the intersection of the equator are at 6 o'clock, and the evening line (day in the west and night in the east) is at 18 o'clock at the meridian where the intersection of the equator is located.

2. Most of the parallels and the morning and dusk lines will form two intersection points, which will divide the latitude into two sections: the day arc and the night arc, of which the midpoint of the day arc is 12 o'clock when it is at the meridian, and the midpoint of the night arc is 0 o'clock (24 o'clock) when it is at the meridian.

3. In the polar daytime zone, there is a parallels tangent to the morning and dusk lines, and the tangent point is always 0 o'clock (24 o'clock) when it is located at the meridian line.

4. In the polar night area, there is a parallels tangent to the morning and dusk lines, and the place where this tangent is located is always 12 o'clock.

Only the spring and autumn equinoxes are perpendicular to the morning and dusk lines, and the others are crossed. On the equator, the morning and dusk lines distinguish between 6:00 and 18:00. I hope you will adopt.

I'm a liberal arts student. It is difficult to describe in words, and you can sum up the experience by doing more questions and analyzing the answers yourself.

In areas where polar day and night occur, except for the lowest latitude, there is no intersection between the morning and dusk lines and the latitudes of the polar day and night regions. The parallels of the polar day and night just appeared, and the morning and dusk lines and these two parallels each had an intersection point, that is, the tangent point. In the Wuji diurnal and nocturnal regions, there are 2 intersections between the morning and dusk lines and the latitude lines.

Tangent refers to the lowest point of intersection between the morning and dusk lines and the parallels, which is the latitude of 66 degrees and 34 minutes.

It's a weft. In addition to the spring and autumn equinoxes, the morning and dusk lines of bai sum up to the two parallels (zhi polar circle to what point dao, excluding the poles) phase.

Switchback (one answer from north to south, the same number of latitudes). So, it doesn't say anything special. For example, on the summer solstice, the sun shines directly on the Tropic of Capricorn, the morning and dusk lines are tangent to the Arctic and Antarctic circles, the polar day within the Arctic Circle, and the polar night within the Antarctic Circle.

Also, as mentioned above, the number of tangent latitudes and the number of direct latitudes are mutually congruent, and so on.

To be precise, the meridian of the tangent point between the morning and dusk lines and the latitude coil is located at 12 o'clock at the meridian place of the day hemisphere, and at 24 o'clock or 0 o'clock when it is located at the meridian point of the night hemisphere.

Since the morning and dusk lines are tangent to the weft coils, the tangent points are in the middle of the morning and dusk lines, bisecting the morning and dusk lines. Therefore, the tangent time in the night hemisphere is 24 o'clock or 0 o'clock, and the tangent time in the day hemisphere is 12 o'clock.

According to the definition of local time: the time when the highest altitude of the sun is specified as 12 o'clock in local time. and the same longitude is the same.

There are 360 degrees of longitude in the world, with a total of 24 hours. In this way, we can get: 0 o'clock longitude, 6 o'clock longitude, 12 o'clock longitude, 18 o'clock longitude (they are equidistant both from time to time and from the position of the meridian).

As can be seen from the figure, the tangent points (a, b) of the morning and dusk lines and the latitude line can be determined by the definition of local time to be 0 o'clock and 12 o'clock.

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It is commonly said that the so-called morning and dusk line refers to the intersection of day and night, not artificial. Therefore, in order to have the existence of the morning and dusk line, there must be the existence of night and day, and the morning and dusk line is a big circle, which must be tangent to a certain weft coil.

The morning and dusk line is the morning and dusk circle, which refers to the dividing line between the day and night hemispheres on the earth, and is the great circle of the earth. Spring and Autumn auspicious two equinoxes, the global day and night are of equal length; Winter and summer solstice, it has the largest angle with the meridian, the largest difference between the length of day and night in the world, due to the atmospheric refraction and the existence of the sun's apparent radius, it is slightly smaller than the big circle.

P.S. **:

The degree of latitude tangent to the line of morning and dusk is the degree of latitude of the point where the sun shines directly.

It is the degree of latitude tangent to the line of morning and dusk + the degree of latitude of the point where the sun shines directly 90 degrees.

For example, if a place is 80 degrees north latitude and a certain day is tangent to the morning and dusk line, then the latitude of the direct sun point on that day is 90 degrees 80 degrees north latitude 10 degrees north latitude.

On the spring and autumn equinoxes, the morning and dusk lines coincide with the meridians. On other days, the morning and dusk lines are oblique to the meridians and have intersections with all meridians. The morning and evening lines each span 180 degrees, as shown in the figure below.

I won't explain it clearly, because at the spring and autumn equinoxes the morning and dusk lines coincide with the meridians across the longitude of 0