Sun Altitude Angle What is the meaning of the declination angle and the solar hour angle

1.The solar altitude angle is the angle at which the sun's rays hit the ground.

2. The declination angle, also known as the declination of the sun, is the angle between the equatorial plane of the earth and the line between the sun and the center of the earth, which is equivalent to the intersection angle of the yellow and red latitude, which is 23 ° 26. The declination angle moves in the range of +23 °27 and -23 °27 on an annual cycle, becoming a sign of the season. The maximum declination reaches +23 °27 on June 21 or 22 every year, which is called the summer solstice, and the sun is located directly above the Tropic of Cancer at noon on this day, which is the day with the longest sunshine time in the northern hemisphere and the shortest sunshine time in the southern hemisphere.

The sun does not see the sun all day in the Antarctic Circle, while the sun does not set in the Arctic Circle, resulting in relatively hot weather in the Northern Hemisphere and colder weather in the Southern Hemisphere. The declination then gradually decreases to 21 or 22 September, which is equal to zero hour, and the time of day and night is equal to the autumnal equinox around the world. The winter solstice is the winter solstice when the declination decreases to a minimum of -23 °27 on December 21 or 22, when the sun shines obliquely in the northern hemisphere, with short days and long nights in the southern hemisphere.

When the declination angle returns to zero, it is the vernal equinox, which is March 21 or 22, and the angle of 3 solar hours is the hour angle of the center of the solar surface. Take the earth as an example, on the earth, at the same time, for people of the same longitude and different latitudes, the corresponding time angle of the sun is the same. The angle of rotation of the earth per unit time is defined as the hour angle w, which stipulates that the noon angle is 0, the morning hour angle is negative, and the afternoon hour angle is positive.

The Earth rotates 360 degrees in one rotation, which corresponds to 24 hours, i.e. the corresponding hour angle of 15 degrees per hour.

Sun altitude angle.

The height of the sun (actually the angle) is the most important factor that determines the amount of solar heat energy received by the earth's surface.

The declination angle is also known as the declination of the sun.

is the angle between the plane of the Earth's equator and the line connecting the Sun and the center of the Earth.

The solar time angle is the time angle of the center of the solar surface, that is, the angular distance from the celestial sphere meridian circle of the observation point along the celestial equator to the time circle where the sun is located.

The relationship between the solar altitude angle and the latitude: the solar altitude angle = 90° - the absolute value of the difference between the local latitude and the latitude of the direct point of the sun.

The solar altitude angle is calculated as h=90°-|where h is the solar altitude angle, the geographic latitude of the observation place is denoted by , and the solar declination (equal to the latitude of the direct point of the sun) is denoted by δ. Therefore, the solar altitude angle = 90° - the absolute value of the difference between the local latitude and the latitude of the point where the sun shines directly.

General law of the angle of solar elevation:

1. Sunrise and sunset, the angle of the sun's elevation in the same place is constantly changing in a day.

2. The altitude of the sun on the morning and dusk line is 0°, indicating that it is experiencing a day and night cycle; The height of the Sun is greater than 0° everywhere in the day hemisphere, indicating daylight; The altitude of the sun is less than 0° everywhere in the night hemisphere, indicating night.

3. In the area between the Tropic of Cancer, the sun reaches its annual maximum when the sun shines directly, not on the summer solstice in the hemisphere.

4. The maximum value (summer solstice day of the hemisphere) and the minimum value (winter solstice day of the hemisphere) once a year on the Tropic of Cancer; The area between the Tropic of Cancer has a maximum twice a year (when the sun is in direct sunlight) and a minimum (the winter solstice in that hemisphere), but twice a year at the equator.

5. In areas outside the Tropic of Capricorn, the maximum value (summer solstice day of the hemisphere) and the minimum value (winter solstice day of the hemisphere) are held once a year.

The relationship between the solar altitude angle and the latitude: the solar altitude angle = 90°-|Local latitude The latitude of the point where the sun shines directly|.

The altitude angle of the sun at noon, the latitude of the direct point of the sun, and the latitude of the earth, any two of these three variables can be found to find the third. For example, the solar elevation angle at noon on the summer solstice (23°26 N) in Beijing (40°N) a, a=90°-(40°-23°26)=73°26.

The solar elevation angle is the angle between the sun's rays in a place and the surface slice that is connected to the center of the earth through that place. When the solar altitude angle is 90°, the solar radiation intensity is the highest. The greater the degree to which the Sun obliquely hits the ground (i.e., the smaller the solar altitude angle), the less intense the solar radiation.

The law of change. 1. The law of latitude change: the latitude and longitude where the direct sun point is located decreases to the north and south.

It can be inferred that the latitude difference from the direct point of the sun is one degree, and the altitude angle of the sun at noon decreases by one degree. (It can be further concluded that the altitude angle of the sun at a certain noon is known, and there are generally two parallels equal to this degree).

For example, if the sun shines directly at 20°N, the elevation angle of the Sun at noon in the world will gradually decrease from 20°N to the north and south, and the solar elevation angle at noon at 19°N is equal to 89°.

That is, the height of the sun at noon at 19°n = 90° - (direct point of the sun - latitude of the place) = 90° - (20° - 19°) = 89°

2. The law of seasonal changes: the direct sun point gradually increases when it moves, and gradually decreases when it moves (the direct sun point is relative to the latitude of a certain place). For example:

For regions at 31°N, the solar elevation angle increases at noon from December 22 (winter solstice) to June 22 (summer solstice), and decreases at noon from June 22 (summer solstice) to December 22 (winter solstice).