The real period of the earth's rotation

Earth rotation: the rotation of the earth from west to east around its axis of rotation, counterclockwise from the North Pole and clockwise from the South Pole. The earth's rotation axis forms an angle of 66.34 degrees with the ecliptic plane and is perpendicular to the equatorial plane. The rotation of the earth is an important movement form of the earth. The average rotation angular velocity is 4. 167× 10-3 degrees/second, and the rotation linear velocity on the equator of the earth is 465 meters/second. It takes 23 hours and 56 minutes for the earth to rotate once, increasing or decreasing by three thousandths to four thousandths of a second every 10 year.

background information

In fact, Philolous, Heritas and others in ancient Greece have mentioned it.

Earth rotation effect diagram

There has always been speculation about the earth's rotation. In the book Dead Bodies during the Warring States Period in China, there is a saying that "the sky is wide on the left and the earth is divided on the right". The confirmation and acceptance of this natural phenomenon was put forward by Copernicus and Heliocentrism 1543.

Time concept editing

The earth's rotation is an important form of the earth's movement.

The average angular velocity is 7.292× 10-5 radians/second, and the linear rotation speed on the equator of the earth is 465 meters/second.

Greenwich Mean Time (GMT) says that one second is 8.6465438+ one tenth of a day, while the earth clock made by 1972 defines one second as the time required for the light emitted by cesium atoms to vibrate 9 19263 1770 times.

Compared with the cesium atom vibration number can maintain a certain speed, Greenwich mean time based on the earth's rotation has changed. Leap second is a concept of time to solve this problem.

Ω = 2π/(24 * 3600s) = 7.27/100000 radians/second.

When the earth rotates, it also rotates. It takes 23 hours, 56 minutes and 4 seconds to rotate once, which is about 0.986 degrees. According to the rotation speed of the earth, it is equivalent to 3 minutes and 56 seconds, time, rotation and revolution time ***24 hours. Every longitude 15 degrees, the local time difference is one hour.

Speed change editing

The observation results of National Institute of Standards and Technology (NIST) show that the earth's rotation speed, which has been slowing down for a long time, has accelerated from 1999. NIST timekeeper said that in order to adjust the Earth's time and atomic clock according to the Earth's rotation speed, during the 27 years from 1972 to 1999, the Earth's standard clock increased by **22 leap second time, but after 1999, the leap second was not increased due to the acceleration of the Earth's rotation speed.

The change of rotation speed After the beginning of the 20th century, an important discovery in astronomy was that the rotation speed of the earth was not uniform. It has been found that the rotation speed of the earth has the following three changes:

① Slow down for a long time. This change makes the length of a day increase by about 1 ~ 2 milliseconds in a century (about 1 second every 35,000 years), which makes the time based on the measurement of the earth's rotation period slow down by more than two hours since 2000. The main reason for the long-term slowdown of the earth's rotation is tidal friction. Scientists found that in the Middle Devonian 370 million years ago, there were about 400 days a year on earth. Therefore, the number of days per day is increasing, while the number of days per year is decreasing. It is estimated that in 200 million years, there will be only 300 days in a year, and a day will become 30 hours.

② Periodic change. From the analysis of astronomical time measurement in 1950s, it is found that the earth's rotation speed varies periodically in seasons, slower in spring and faster in autumn, and periodically in half a year. The annual variation range is about 20 ~ 25 ms, which is mainly caused by the seasonal variation of wind.

③ Irregular changes. There are still irregular changes in the earth's rotation, fast and slow. The reasons need to be further analyzed and studied.

The slow rotation of the earth is also closely related to human activities, especially the launch of artificial earth satellites, and its reaction force directly slows down the rotation of the earth. According to the principle of conservation of momentum, this factor should be the main reason for the slow rotation of the earth. Therefore, for the safety of the earth, satellites launched by humans should no longer rely on the momentum of the earth's rotation.

Rotation meaning editing

Alternate day and night

1. reason: the earth is not luminous and opaque, and the earth rotates.

2. Period: 1 solar day, that is, 24 hours.

3. The meaning of the termination line: the dividing line between the day and night hemisphere, including the morning line and the dark line. Definition of terminator line: ① Rotation method: along the direction of the earth's rotation, from night to day, it is the morning line; It is a blurred line from day to night. ② Time method: The local time on the equator is 6 o'clock, corresponding to the morning line; The local time on the equator is 18, which corresponds to the dark line. ③ Azimuth method: morning line on the east side and dark line on the west side of the night hemisphere; During the day, there is a dark line on the east side of the hemisphere and a morning line on the west side.

Local time and time zone

1. local time

The concept of local time: taking the local meridian plane as the starting plane, the time determined by celestial bodies at any time is called local time.

Reason: Sunrise is seen earlier in the East than in the West, earlier in the East and later in the West.

Calculation method: the time of the sought position = the time of the known position (longitude between two places ÷ 15) × 1 hour (the sought position east of the known position is indicated by "+",and vice versa.

2. Time zone and time zone

Meaning of time zone: Time zone refers to areas with the same time system.

Division of time zones: The global * * * is divided into 24 time zones, which are based on the prime meridian, from 7.5 W east to 7.5 E, and are divided into one time zone, which is called the middle time zone or the zero time zone. To the east of the zero-time zone, it is divided into East Zone 1 to East Zone 12 in turn; The west of the middle time zone is divided into west 1 zone to west 12 zone, and the east 12 zone and the west 12 zone are combined into a time zone with longitude of 7.5, that is, twelve zones.

Meaning of time zone: For the convenience of timing, the local time of the central meridian of each time zone is regarded as the common time of the instant zone of the whole time zone.

Time zone calculation: the time zone difference of the searched location = known location × 1 hour (calculation of the time zone where a location is located: the quotient of the longitude of the location ÷ 15 is rounded to an integer, which is the number of time zones, and the east and west time zones are determined according to the longitude; Calculation of time zone difference: if the two places belong to the eastern time zone or the western time zone, the time zone difference is the difference between the two places; If the two places belong to the eastern time zone and the western time zone, the time zone difference between the two places is the sum of the two time zones; Selection of "+"and "-":If the calculation place is located in the east of the known place, use "+"and vice versa.

Relationship between local time and time zone: Generally, the time read from the illumination map is the local time. When the solar altitude angle is the largest at noon in an area, it must be 12 local time. Because the time zone comes from local time, it is the place of the central meridian of a time zone, and the two are closely related. The time difference between the two places can be hours, minutes and seconds, and the time difference between the two places can only be hours.

3. International international date line

Concept: internationally, the meridian of 180 between east and west regions is regarded as the international international date line, which is called international date line for short.

Characteristics of the date line: the date line is the beginning of a new day and the end of an old day on the earth, and the replacement of dates on the earth begins from this line. The date line is not a straight line, but it has some twists and turns and does not extend completely according to the longitude 180. this is

In order to facilitate the residents of nearby countries and regions, Japan's border demarcation avoids passing through land.

Date change when crossing international date line: At any moment, the East 12 area is always 24 hours earlier than the West 12 area, that is, one day earlier. Therefore, from the east 12 area to the east, the date will be shortened by one day; From the west 12 area to the west, the date is increased by one day. At the same time, there are 12 districts in the east and west, but the dates are one day apart.

Deflection of an object moving horizontally along a surface

The rotation of the earth will also cause objects moving horizontally in any direction on the earth to deviate from the original direction. Based on the moving direction of the moving object, the horizontal object in the northern hemisphere leans to the right and the southern hemisphere leans to the left.

The reason why horizontal objects deflect on the surface is that all objects have inertia and try to keep their own speed and direction. As mentioned above, the horizontal direction on the earth is based on latitude and longitude, the longitudinal direction is the north-south direction and the latitude direction is the east-west direction. However, due to the rotation of the earth, the latitude and longitude, as the standard of north-south and east-west directions, deviated with the autobiography of the earth. Therefore, the horizontal motion of objects that really keep the same direction, if represented by the direction on the earth, is relatively deflected.

The Sunday motion of celestial bodies

The Sunday motion of celestial bodies is a reflection of the earth's rotation. People call the systematic apparent motion of the sun, moon and stars on the celestial sphere from east to west as the celestial Sunday apparent motion. [ 1]

Ontology motion editing

The position of the earth's rotation axis on the earth's body is constantly changing, which is called the pole shift, or simply the pole shift. 1765 L Euler proved that if there is no external force, the rotation axis of the rigid earth will swing freely around the shape axis with a period of 305 sidereal day. It was not until 1888 that people confirmed the existence of the pole shift from the observation of latitude changes. In 189 1, S.C. Zhang Dele of the United States further pointed out that the pole shift includes two main periodic components: one is a free swing with a period of about 14 months, also known as Zhang Dele swing; The other is forced oscillation with a period of 12 months.

The actual observed Chandler swing is the free swing predicted by Euler. But because the earth is not an absolute rigid body, Zhang Dele's swing period is about 40% longer than predicted by Euler. Zhang Dele's swing amplitude changes slowly from 0.06 "to 0.25", and its period changes from 4 10 to 440 days. Another major component of the pole shift is the annual forced oscillation with an amplitude of about 0.09 ",which is relatively stable, mainly due to the seasonal changes of the atmosphere and polar ice and snow.

Secular polar motion can be obtained by removing the periodic components in the pole shift. The average speed in secular polar motion is about 0.003 "/ year, and the direction is about 70 west longitude.

Spatial motion editing

The polar radius of the earth is about 1/300 shorter than the equatorial radius, and at the same time,

Foucault pendulum

Foucault pendulum

The equatorial plane of the earth's rotation, the ecliptic plane of the earth's revolution around the sun and the white plane of the moon's revolution around the earth are not on the same plane. Because of these factors, the rotation axis of the earth has complex motion in space under the gravity of the moon, the sun and the planets. This movement is usually called precession and nutation. Precession movement shows that the earth's rotation axis rotates around the ecliptic axis, and it takes about 26,000 years to draw a cone in space. Nutation is the superposition of many complex periodic motions on precession motion. The earth's axis always points to Polaris and never changes. In the orbit of the sun, when the motion time is equal, the arc areas of the earth and the sun are equal.

Proofreading method editing

Shell method

The earth is constantly rotating, and objects moving horizontally on the ground will inevitably shift to the right (northern hemisphere) or to the left (southern hemisphere). According to this phenomenon, people can prove that the earth is rotating by analyzing the direction of the projectile.

Gravity method

The earth keeps spinning. Due to the inertial centrifugal force, the acceleration of gravity on the ground must be the smallest at the equator and the largest at the poles. The earth can't be a right sphere, but a rotating ellipsoid with slightly protruding equator and slightly flat poles. The results of gravity survey and circular arc survey confirm the correctness of these views and also confirm the rotation of the earth from one side.

Measurement method

The earth rotates all the time, because the rotation speed increases with height. In the process of falling from a height, objects will inevitably have a higher rotation speed to the east and will inevitably fall to the east. To prove this, someone once did an experiment in a deep well. The test results show that objects falling from the center of the wellhead always collide with the east wall of the mine at a certain depth, which proves the rotation movement of the earth from another side.

Rotation editing

Polar motion

The movement of the earth's axis on the ground is called the pole shift.

There are two main reasons for the pole shift. One is that the earth axis deviates from the inertial axis, and the period is about 14 months. The other is caused by the seasonal operation of the atmosphere, and its cycle is one year. There are other secondary reasons, and the amplitude of the pole shift generally does not exceed 15 meters.

As a result of the pole shift, the latitude and longitude on the earth have changed.

troops

The change of the position of the celestial pole on the celestial sphere is called precession.

1. regularity:

The precession of the earth's axis is a conical motion, and its regularity is as follows:

The axis of the cone is perpendicular to the earth's orbital plane and points to the pole of the ecliptic.

The radius of a cone is the intersection of yellow and red.

The direction of motion is from east to west, which is opposite to the rotation direction of the earth.

The movement speed is 50 seconds and 29 minutes per year, and the cycle is 25,800 years.

2. Performance:

The periodic motion of celestial pole causes the change of Polaris.

The equatorial plane of the earth and the celestial equator have undergone systematic changes.

Vernal equinox moves westward at the speed of 50 seconds and 29 minutes on the ecliptic every year. (precession)

Make the tropic year less than the sidereal year.

3. Reason:

First, the shape of the earth.

Because the earth is an obvious oblate sphere, the additional gravity of the uplift part

earth rotation

earth rotation

Always a little bigger than the other side. The difference between the two always exists on the side near the sun and the moon.

Second, Huang Chijiao.

Because of the ecliptic angle, the sun and the moon often exert gravity on the equatorial uplift outside the equatorial plane. In this way, the gravity difference above becomes a moment, which makes the earth axis close to the yellow axis and the celestial pole close to the yellow pole.

Third, the earth rotates.

Due to the above gravity difference, the angular momentum of the earth's rotation increases by an increment, which makes the direction of the earth's rotation deflect. This is the precession of the earth's axis, which is precession.

Reason editor

Suppose there is an ether in the universe. Because the existence of the ether is infinite and it is always moving, the earth and the sun are both in the ether. Both the earth and the sun will be forced by the ether and begin to move in the direction of the ether. The earth will be attracted by the sun when it is subjected to etheric force. Under the action of these two decisive forces, the earth will begin to rotate.

Gyroscope and Earth

Gyroscope and Earth

Various theories or hypotheses about the earth's rotation. Considering that the reason of the earth's rotation should be combined with the earth's revolution, there is no absolutely stationary object in the universe, and the massive celestial bodies subjected to various external forces must rely on rotation to maintain their balance in order to maintain their own movement. Small-mass particles must also rely on rotation to maintain their own movement balance because of their extremely fast movement speed. This can refer to the motion principle of gyro, and the rotating object has a high tolerance for external forces in motion.

According to the traditional view, the sun and planets are both formed in a huge primitive rotating nebula. When these primitive rotating nebula materials shrink by themselves under their own gravity, due to the conservation of angular momentum, the more they shrink, the greater their density and the faster their rotation speed. When the planet is formed, the rotational angular momentum of the nebula material becomes the rotational angular momentum. First of all, the solar system originated from a nebula, which is a hypothesis in itself, so the traditional explanation of the origin of the earth's rotation is uncertain. We should not regard this explanation as the golden rule. Secondly, this traditional explanation has many things that cannot be justified. According to this view, the protonebula should rotate in the same direction with basically the same angular velocity, which is why it forms such a shape.

earth rotation

earth rotation

The greater the mass, the faster its rotation speed, and all celestial bodies in the solar system should revolve and rotate in the same direction. However, the current situation of the solar system is not the case. First, the mass of the sun is about 750 times of the total mass of the planet, accounting for more than 99% of the mass of the whole solar system, but its angular momentum only accounts for 2% of the whole system. Although the planet's mass is small, its angular momentum is large; Second, most celestial bodies in the solar system rotate counterclockwise (including revolution and rotation), but Venus and a few satellites rotate clockwise.

Because there are many loopholes in the traditional explanation of the earth's rotation, some scholars have put forward some new explanations.

An American astronomer thinks that primitive planets don't rotate. The attraction of the sun to the primitive planet makes it protrude to the side of the sun. When the primitive planet revolves around the sun, the bulge deviates from the direction toward the sun, but the attraction of the sun to the bulge pulls it back to the direction toward the sun, thus forcing the planet to rotate. Of course, astronomers' explanations also have many problems. For example, why do most planets rotate counterclockwise, while Venus rotates clockwise and Uranus rotates while lying down?

Modern scientific research shows that the rotation of the earth is not static. The most prominent is our earth, whose rotation fluctuates obviously: in a year, the fastest rotation of the earth is in August, and the slowest rotation is in March-April. Rotation is not uniform in different centuries and years. For example, the earth's rotation was relatively fast in17th century, accelerated in 1930s and 40s, slowed down in 1960s and 1970s, and accelerated again in 1980s and 1990s.

The rotation of the earth is constantly changing, which shows that there is a kind of power that accelerates and decelerates the rotation of the earth. So, what is this driving force?

Some people say that the change of the earth's rotation is related to the South Pole. The huge glaciers in Antarctica are slowly melting, that is to say, the ice on the Antarctic continent is decreasing and its weight is decreasing. In this way, the earth lost its balance and affected its rotation speed. However, this change is one-way, and it is impossible to speed up and slow down the rotation of the earth.

Another explanation is that the monsoon affects the rotation of the earth. Some scientists have calculated that the air that the monsoon shifts from the mainland to the ocean and from the ocean to the mainland every year weighs 3 trillion tons. The transfer of such heavy matter from one part of the earth to another can affect the center of gravity of the earth, change the angular momentum distribution of the earth, and accelerate or decelerate the rotation of the earth.