Why is the 1 return year 20 minutes and 24 seconds shorter than the 1 sidereal year?

Because one is based on the sun and the other is on a star at infinity.

The sidereal year is the actual time interval required by the Earth to make one revolution around the Sun, and as the name suggests, it is the time it takes to observe from the Earth, starting from the same position as the Sun and a certain star, and then returning to this position when the Sun is observed.

Return year: The time it takes for the sun to make one circumference around the celestial sphere on Earth, that is, the time it takes for the center of the Sun to travel from the vernal equinox to the vernal equinox, is also known as the solar year.

Due to the gravitational influence of the Moon, the Sun and the planets, the axis of rotation of the elliptical Earth, which is more prominent at the equator, moves slowly around the ecliptic (the corresponding vernal equinox retreats westward along the ecliptic at an annual equinox rate, moving westward by 1 degree in about 71 years, or about one week in about 25,800 years), that is, precession. The vernal equinox moves slowly westward on the ecliptic, about every year, that is to say, the position of this vernal equinox when the earth turns back is not the position of its last equinox, and this position moves towards it for a distance, so the path of movement is shorter, and the period is shorter than the real period, about 20 minutes and 40 seconds shorter per year, which is the difference between the sidereal year and the return year.

The sidereal year, which is the time it takes for the earth to revolve 360 degrees around the sun, is the real meaning of the earth's orbital cycle.

The year of return is the time when the sun shines directly on the Tropic of Cancer for one week. In other words, the time difference between the last time the sun hit the Tropic of Cancer and this time the sun directly hit the Tropic of Cancer is called a return year. It's a year in the usual sense.

These two times are not the same.

The meaning of the sidereal year is easy to understand. Let's explain it again in the year of the return. We know that because the Earth's axis of rotation and the ecliptic plane (the plane of the Earth's orbit) have an angle.

The presence of this angle causes the direct rays of the sun to move back and forth between the Tropic of Capricorn. Start shooting straight at the Tropic of Capricorn, then slowly move south, shoot to the equator, and then shoot to the Tropic of Capricorn. Then return, shoot to the equator, shoot to the Tropic of Cancer, complete a cycle, a cycle.

The angle between the ecliptic plane (caused by revolution) and the axis of rotation leads to the change of seasons, and the change of seasons produces years. So what we usually call a year is a return year.

--Actually, there are still some people who don't understand ---

Additional note: We usually say that the revolution leads to the change of seasons. That's right. But if there is no angle between the axis of rotation and the orbital surface, there are no seasons. )

So, why is the regression year smaller than the sidereal year? Why is the time difference between the two direct sunlight hitting the Tropic of Cancer equal to the time of the revolution of 360 degrees? Or is it because of the rotation of the Earth.

Because in addition to the rotation of the earth, in addition to the axis of rotation and the ecliptic plane have angles. The axis of rotation itself is still moving in a circle. And the direction of this circular motion is opposite to the direction of the Earth's rotation.

Year of Return: The time elapsed by the center of the sun's apparent circle twice in succession at the equinox. Also known as the "Year of the Sun". The return year is about 20 minutes and 23 seconds shorter than the sidereal year, and the return year is 5:48:46 on the 365th lunar day.

Sidereal year The time it takes for the Earth to make one revolution around the Sun. Used only in astronomy. It is equal to a mean solar day, or 6 hours and 9 minutes and seconds on 365 days.

Precession Because the direction of the Earth's axis of rotation rotates slowly around the ecliptic, the vernal equinox (the ecliptic node) is constantly moving westward relative to the same point of the ecliptic, and the velocity is about 25,800 years of arc seconds, which is about 25,800 years. The sidereal year is the Earth's orbital period and is relatively constant. The return period of the direct point of the sun is shorter than that of the sidereal year due to the precession, and the sidereal year is about 20 minutes and 23 seconds longer than the return year.

Hence the sidereal year is longer than the return year.

1 return year = days, i.e. 365 days, 5 hours, 48 minutes and 46 seconds.

1 sidereal year = day, i.e. 365 days, 6 hours, 9 minutes and 10 seconds.

Tropical year: The time interval between the two consecutive passes of the vernal equinox by the flat sun, that is, the time elapsed by the center of the sun from west to east along the ecliptic from the vernal equinox to the vernal equinox, also known as the solar year. The return year is a cycle of four seasons, and like the sidereal year, it is also the rotation cycle of the earth, and the reason why they are different is because of the different time systems used, and the differential rotation of the earth shortens the time of the return year.

Based on the length of time in each regression year from 1980 to 2100 A.D., 1 regression year = day, i.e. 365 days, 5 hours, 48 minutes and 46 seconds. This is calculated based on the average of 121 regression years. The length of each return year is not equal.

The sidereal year is the actual time interval required by the Earth to make one revolution around the Sun, that is, the time it takes to observe from the Earth, starting from the same position of the Sun and a certain star, and when the Sun is observed to return to this position, it is only used in astronomy. A sidereal year is equal to a mean solar day or 365 days at 6 hours, 9 minutes and 10 seconds. The sidereal year is measured in days, i.e. 365 days, 6 hours, 9 minutes and 10 seconds.

Tropical year: The time it takes for the sun to make one circumference around the celestial sphere from the ecliptic of the celestial sphere from the earth, that is, the time that the center of the sun travels from the vernal equinox to the vernal equinox, also known as the solar year. 1 return year = days 365 days, 5 hours, 48 minutes and seconds.

A return year is not the same as a sidereal year. A sidereal year is the time it takes for the Earth to revolve around 360 degrees, 1 sidereal year = day = 365 days, 6 hours, 9 minutes, 10 seconds, and it is applied to astronomy, not to the calendar.

The reason for the time difference between sidereal years and return years is that they take different timers.

The return year is the calendar year time synchronized with the true solar time formed by the earth and the sun, and the true solar time on the surface of the earth's crust (*natural timer) is affected by solid tides, and the angle of rotation varies from year to year, and the time of the return year is also different.

The sidereal year uses an artificial timer and is not affected by solid tides.

The reference object is different.

A sidereal year is a reference to a distant star that orbits the Earth at an angle of 360 degrees. It is the true cycle of the Earth's revolution. It took 365 days, 6 hours, 9 minutes and 10 seconds.

The return year is based on the vernal equinox, and the direct point of the sun moves back and forth between the Tropic of Cancer. A return year is the time taken from the spring equinox (the sun directly hitting the equator) (all in the northern hemisphere), passing through the summer solstice (direct to the Tropic of Cancer), the autumn equinox (direct to the equator), the winter solstice (direct to the Tropic of Capricorn), and then back to the next vernal equinox. Here the sun revolves a little more than 359 degrees, so it takes a little less time.

Time: 365 days, 5:48:46.

The reason is the slight change of the earth's axis, the earth's axis is not fixed, but is doing a very slow periodic movement, the direction is opposite to the direction of the earth's revolution, the period is 25,800 years, we call this movement the earth's axis precession. This precession causes the vernal equinox to move westward by about 50 minutes and 29 seconds (angle) every year, which we call the node retreat, which makes the return year not turn 360 degrees, so the time is shorter.

The frame of reference is different.

The sidereal year is based on distant stars, and the return year is based on the Sun.

This is because they refer to different objects.

A sidereal year is the time it takes for a star other than the Sun to revolve around the Earth, which makes the Earth's true rotation time; The return year is divided by reference to the return movement of the Sun on Earth, taking into account the movement of the Sun itself.

The sidereal year differs from the return year in time because they employ a different timer. The sidereal year employs an artificial timer. The return year features a natural timer.

Solid tides cause the earth's crust to rotate at an uneven rate, resulting in a different time for each return year.

The return year is calculated at a point on the earth, after one revolution around the sun, and then aligned with the sun.

A sidereal year is calculated as a point on the Earth, after one revolution around the Sun, and then aligns with a certain star (as a fixed point).

So the return year turned a little more.

The return year is a calendar year that is timed in true solar time produced by the earth's crust and the sun. The sidereal year, on the other hand, is clocked time. The cumulative one-year time difference between true solar time and clock time is precession.

The year of return is a calendar year that is taken in true solar time (natural timekeeper) on the surface of the earth's crust. And the sidereal year adopts an artificial timer.

Because they use different timers, the sidereal year uses a human timer, and the return year uses a natural timer. The time difference between the two timers accumulated by one year is precession.