What is sidereal time, true solar time, mean solar time, universal time, and what is the local time?

Here are the explanations of the various concepts of time:

A day is defined as the time it takes for the Earth to rotate around one time, while sidereal time is a measure of time based on the sun's motion of the stars.

2.True Solar Time: True solar time measures the position of the sun in the sky using the sun as a reference point. Since the Earth's orbit around the Sun is elliptical, the length of time each day in true solar time will vary slightly.

3.Mean Solar Time: Mean solar time is also known as Greenwich mean time (GMT).

It is the average value of the measured time based on the meridian of the Greenwich Observatory in the United Kingdom. Mean solar time is widely used in standard time around the world.

4.Universal Time (UT): Universal Time is created to account for the time differences between different geographical locations.

It is based on Greenwich Mean Time, and the time is evenly distributed among different geographical locations according to the speed of the Earth's rotation and revolution.

5.Local time: Local time is a measure of time based on the meridian of a specific geographic location. When each geographical location has its own place, this is because the rotation speed of the earth will vary in different geographical locations.

These concepts of time are time systems based on the rotation and revolution of the earth as reference points, and are produced according to different needs.

Sidereal time is the time when the earth is observed by the star, due to the error in distance, it is generally measured in the earth year, the true solar time is the time when the sun is the point, and the time when the earth circles back to the point, and the universal time is the rotation of the earth.

The resulting day-night alternation time, local time is the time when day and night alternate at the same longitude, and the time in which the longitude is located is named in an important city, for example, Beijing time and Shanghai time are in the East Eighth District.

It is subject to the time of the capital Beijing, the territory of the United States.

It is separated by Canada, so there is Eastern Time and Western Time.

1. Stellar time: [star] passes through the time interval of the upper midheaven twice in a row.

2. Flat (true) solar time: The time interval between the [sun] passing through the upper middle heaven twice in a row.

3. Universal time: It is the standard Greenwich Mean Time at the [Greenwich] Observatory in London, England.

4. Local time: different moments occur due to different [longitude].

The Earth's rotation period has two periods, one is the solar day (i.e. 24 hours) with the Sun as a reference, and in one solar day, the Earth rotates 360°59; One is based on a star, and in a sidereal day, the Earth rotates only 360 times in 23 hours, 56 minutes, and 4 seconds. As shown in the figure, the angle I marked in the figure is the 59 more rotations of the earth in the solar day, which is actually the angle of the earth's revolution in a solar day.

To put it simply;

A "sidereal day" is the time it takes for the Earth to truly rotate once (23 hours, 56 minutes, and 4 seconds).

The "solar day" is the time it takes for the Earth to truly rotate once plus the time it takes to revolutionize (23 hours, 56 minutes, 4 seconds, 3 minutes and 56 seconds = 24 hours).

Simply put, a sidereal day is the time interval between two arrivals of the same star at the same position in the sky (usually the position of the local meridian); If you replace the star with the sun, it becomes a true solar day; Since the apparent motion of the sun is irregular (in fact, the speed at which the earth revolves around the sun is uneven), the true solar days of each day are not equal, so astronomers devised an imaginary celestial body, the flat sun, and the time interval between the flat sun reaching the same position in the sky is a mean solar day, and the average solar day is uniform.

The solar day is also called the earth day, the sidereal day is based on the star, and the solar day is based on the sun.

On a sidereal day, the Earth rotated 360 degrees in 23:56:4.

In one solar day, the Earth rotated 360 degrees and 56 minutes in 24 hours.

The difference between the two is that the Earth rotates around the Sun at the same time. If the Earth does not revolve, then it is the same with the Sun or the stars as a reference point.

But the earth rotates and rotates in the same direction, so when facing the sun twice at the same point, it is not only 360 degrees, but it should be 360 degrees and 56 minutes; If (assuming) the direction of revolution and the direction of rotation are opposite, then the same point is 359 degrees 04 minutes in the face of the sun's void twice;

If a distant star is used as a reference point, then the rotation of the earth can be ignored, and it can be approximated as the rotation in situ, so the time is shorter than the solar day.

So how do you calculate the time spent on the extra 56 points?

Knowing that the earth's revolution is a day, then the average angular velocity of the earth per day is 360 degrees day = this average velocity multiplied by the angle is considered the time of the world's pants.

The solar day is the interval between the Earth facing the Sun, while the sidereal day is the interval between the Earth facing a star in the starry sky, which is the true rotation period.

Originally, if the earth was fixed in the universe and did not revolve around the sun, it should indeed be rotated 360 degrees to face the sun again, but in fact, the earth is revolving around the sun, and after the earth's rotation of 360 degrees (sidereal day), the earth has moved some distance, and it has not been able to face the sun again, and it has to turn a little more, so the sidereal day is shorter than the solar day.

A return year is a solar day. During this period, the Earth rotates in a circle, which is exactly 1 more than the number of days (one revolution makes the annual rotation difference between the number of rotations and the number of days in the year by 1), which means that there are so many sidereal days in a year.

Therefore, the ratio of the length of the sidereal day to the solar day is: , this ratio is very important, if the denominator is the 24 hours of the solar day, then the sidereal day of the numerator is 23:56:04 seconds according to this ratio, that is, the sidereal day is 3 minutes and 56 seconds shorter than the solar day.

Let's start with the definition of solar day and sidereal day.

The solar day is the time interval when a certain place on the earth reaches the maximum altitude angle twice in a row, and the sidereal day is the time interval between two consecutive places on the earth facing a distant star (my own understanding may be different from the textbook), but the earth revolves around the sun, or in other words, the solar day only involves the rotation of the earth, not the revolution of the earth, while the sidereal day involves both the rotation of the earth and the revolution of the earth. As a result, there is a difference in the length of time between a solar day and a sidereal day.

Take a look at the diagram below.

When the Earth is at point A, point P on the Earth is facing both the Sun and the distant star. Start the timer. After the Earth has rotated almost once, it has reached point b in its orbit, and point p is again facing the distant star, which is a full sidereal day.

But you see, is the p-spot facing the sun again? Is it a solar day? Not yet.

Since the Earth is revolving around the Sun at the same time as it rotates, it has also moved some distance in its orbit in the time of a sidereal day, and it needs to turn a little more angle before it is facing the Sun again. When the Earth reaches position C, this point is reversed, and point P is facing the Sun again, and the time for a solar day has arrived. But at this time, the p-point is no longer directly opposite the star.

Right? A sidereal day is simply the time it takes for the Earth to go from point A to point B, which is 23 hours, 56 minutes and 04 seconds. A solar day is the time it takes for the Earth to travel from point A to point C in its orbit, which is 24 hours. Namely:

The time it takes for the Earth to travel from point B to point C is 3 minutes and 56 seconds. Thus, the time of a sidereal day is 23 hours, 56 minutes and 04 seconds, but the Earth needs to travel another 3 minutes and 56 seconds, and it takes exactly 24 hours to complete a solar day.

This is how the time difference between the solar day and the sidereal day comes about.

Both the solar day and the sidereal day are made up of two parts; 1. Rotation; 2. Revolution.

The Earth revolves only around the Sun. The Earth's orbital motion is like a pendulum swinging back and forth to distant stars. The revolution time swinging to the left is canceled out by the revolution time swinging to the right, and the time of the sidereal revolution is 0.

So there is only one component of a sidereal day, which is rotation.

Solar day = rotation (23 hours 56 minutes 4 seconds) + revolution (3 minutes 56 seconds) sidereal day = rotation (23 hours 56 minutes 4 seconds) + revolution (0 seconds).

Yes, that's the right way to put it.

A lunar day is the time it takes for the Moon to pass the same meridian circle twice in succession, with an average of 24 hours and 50 minutes.

A solar day is the time interval between two consecutive passes of the Sun on the same meridian, which is 24 hours.

A sidereal day is the time interval between two meridians facing the same star, and is the period in which the Earth truly rotates 360 degrees, which is 23 hours, 56 minutes, and 4 seconds.

Therefore, the cloudy day is the longest, about 50 minutes longer than the solar day. The sidereal day is the shortest, 3 minutes and 56 seconds shorter than the solar day.

Solar day. and sidereal days are composed of two components; Rotation + revolution.

The reason for the difference between the sidereal day and the solar day is that the earth revolves around the sun and not around the star. The Earth's orbit around the Sun is like a pendulum swinging left and right to the left and the time produced by the right swing canceling each other out to zero. So sidereal days are made up of only one component.

Solar day = rotation (23 hours 56 minutes 4 seconds) + revolution (3 minutes 56 seconds).

sidereal day = rotation (23:56:4 seconds) + revolution (0 seconds).

1. Stellar time: [star] passes through the time interval of the upper midheaven twice in a row.

2. Flat (true) solar time: Li Haoyin [sun] passes through the upper middle heaven twice in a row.

3. Socks slow down the world time.

It is the standard Greenwich Mean Time at the Greenwich Observatory in London, England.

4. Local time: different moments occur due to different [longitude].