The universe is composed of celestial bodies, and the celestial bodies are in eternal motion, and the eternal motion between celestial bodies is one of the basic conditions for maintaining the universe, and the movement of celestial bodies in the universe is extremely complex. For example, the earth we live on is doing complex movements, on the one hand, the earth itself is rotating, and at the same time doing orbital movement around the sun, and it is also doing a revolving motion around the center of the milky way with the entire solar system, of course, the entire milky way is also in motion.
The rotational motion of the Earth
The movement of the earth is a complex synthesis of all movements, of which the rotation and rotation of the earth are the two most basic movements, and today we will talk about the rotational movement of the earth. The rotation of the earth refers to the earth around the center of the solar system of the celestial body the sun to do a rotational motion, the orbital plane of the earth's rotation is called the ecliptic plane, the orbital plane of the eight planets of the solar system is almost all on one plane, which is the coplanarity of the orbit of the eight planets.
Schematic diagram of the orbits of the eight planets
The orbit of the Earth's rotation is an approximately perfectly circular elliptical orbit, the Sun is located on one focal point of the ellipse, and the average radius of the Earth's orbit around the Sun is about 150 million kilometers, called an astronomical unit. Of course, since the Earth's orbit is an elliptical orbit, the distance from the Sun changes in the process of rotation, and the closest distance to the Sun is about 147 million kilometers, which is called perihelion; the farthest distance from the Sun is about 152 million kilometers, which is called the aphelion.
Schematics of perihelion and aphelion points
The perihelion of the Earth's rotation arrives around the beginning of January each year, when the Earth's rotation is the fastest, while the aphelion arrives around the beginning of July every year, when the Earth's rotation is the slowest. The time required for the rotation of the earth is the cycle of the rotation, that is, one year, of course, how we observe the rotation of the earth, we also have to choose the reference. Using distant stars as a reference object, the true period of the Earth's rotation is 365 days, 6 hours, 9 minutes and 10 seconds, which is called a stellar day.
Schematic diagram of the orbit of the eight planets
In addition, if the direct point of the sun is moved as a reference, the resulting orbital period is called a regression year, and the time is 365 days, 5 hours, 48 minutes and 46 seconds. The Earth's orbit also has angular velocity and linear velocity, the Earth orbits the Sun in a year, that is, 360 °, the angular velocity of the Earth's orbit is about 59′ per day. The total length of the Earth's orbit is about 940 million kilometers, and the linear velocity of the Earth's rotation is about 29.8 kilometers per second, that is, about 30 kilometers per second, and about 2.57 million kilometers per day.
Schematic diagram of the yellow-red intersection angle
Since the ecliptic plane of the orbital plane of the Earth's orbit and the equatorial plane of the Earth's rotation do not coincide, but there is an angle between them, we call it the yellow-red intersection angle, and the current degree of the yellow-red intersection angle is about 23.5°. Due to the existence of the yellow-red angle, it leads to the movement of the direct solar point, that is, once in a year, the direct solar point returns and turns between the Tropic of Cancer, resulting in a two-second to two-day.
Schematic diagram from 2 minutes to 2 days
When the direct point of the sun moves from south to north, the day when it passes through the equator, it is the vernal equinox day, mostly around March 21; when the direct point of the sun moves from north to south, the day when it passes through the equator, it is the autumn equinox day, mostly around September 23; when the direct point of the sun moves north to the northernmost position, it is the summer solstice day, mostly around June 22; when the direct sun point moves south to the southernmost position, it is the winter solstice day, mostly around December 22. Due to the movement of the direct point of the sun, a series of geographical significance such as the change of the length of the earth's day and night, the change of the height of the noon sun, and the division of the four seasons and the five belts have been generated.