Why is the return year shorter than the sidereal year

The sidereal year is the time it takes for the Earth to revolve 360 degrees around the Sun, which is the true revolution of the Earth.

Cycle. The year of return is when the sun is at the Tropic of Capricorn.

Direct shot for a week's time. Or rather, the last time the sun shined.

The time difference between the direct Tropic of Cancer and the current direct sunlight hitting 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 because of the rotation of the Earth.

axes and ecliptic planes.

Earth's orbital plane) is to 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.

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.

Different metering systems, different calculation times, and different lengths of time.

Tropical year

Also known as the solar year, it refers to the time interval between the two consecutive passes of the vernal equinox, 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. The return year is a four-season cycle, and like the sidereal year, it is also the earth's orbital cycle, and the reason why they are different in time is because of the different time systems used, and the earth's differential rotation shortens the time of the return year.

Tropical year: Also known as the solar year, it refers to the time interval between the two consecutive passes of the vernal equinox, 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. The return year is a cycle of four seasons, and like the sidereal year, it is also the rotation period of the earth, and the reason why they are different in time is that the time system used is different, and the differential rotation of the earth shortens the time of the return year.

Year of the Sun, which refers to the time interval between the two consecutive passes of the sun through the vernal equinox, that is, the time elapsed by the sun's center from west to east along the ecliptic from the vernal equinox to the vernal equinox. It is too unjustifiable that the year of the sun is also known as the year of return, and the year of return is the day, that is, 365 days, 5 hours, 48 minutes and 46 seconds. This is based on the average of 121 regression years.

The result of the calculation. The length of each return year is not equal. Astronomers according to the solar system.

The rules of operation compiled the "perpetual calendar".

1. The reference object is different.

The sidereal year is based on a distant star and the Earth's orbit angle is 360 degrees, which is the true cycle of the Earth's revolution, with a duration of 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 starts from the spring equinox (the sun directly hits the equator) (taking the northern hemisphere as an example), passes through the summer solstice (directly hits the Tropic of Capricorn), the autumn equinox (hits the equator), the winter solstice (hits the Tropic of Capricorn), and then returns to the time taken for the next vernal equinox, the sun revolves a little more than 359 degrees, so it takes a little less time, and the duration is 5:48:46 on the 365th.

2. The time is different.

Due to the slight movement of the Earth's axis, the Earth's axis is not fixed, but does a very slow periodic motion in the opposite direction of the Earth's revolution, and this movement is called the Earth's axis precession. This precession shifts the vernal equinox westward by about 50 minutes and 29 seconds each year, a phenomenon known as the receding node, which makes the return year not turn 360 degrees, so the duration is shorter.

Punctuality of the sidereal year:

Even in the eastern sky at dawn, it is impossible to see the sun and stars at the same time, so you have to wait.

It takes a week or two to see the phenomenon of movement. For example, in July in the Northern Hemisphere, Orion is not visible in the dawn sky, but in August it is visible. After a year, all the constellations rotate in the sky for one week.

A movement that will be noticed and easy to measure if you observe the sky regularly before dawn is the movement of the sunrise position in a north-south direction.

The return year, defined by this movement, is the basis of the Gregorian calendar, which is why many civilizations begin the year on the day when a particular star (such as Sirius) can be observed at dawn in the east. In the epic poet Hesiod's Work and the Days, the year of the year is determined by reference to the day when a particular star is first seen at dawn.

[Astronomy 9] What is precession? What is the difference between a sidereal year and a return year? The precession and nutation of the earth.

First, the nature is different.

1. The sidereal year refers to the time interval actually required for the earth to circle the sun, that is, the time required 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.

2. Tropical year: also known as the solar year, it refers to the time interval between the two consecutive passes of the vernal equinox by the flat sun, that is, the time experienced by the center of the sun from west to east along the ecliptic from the vernal equinox to the vernal equinox.

Second, the adoption system is different.

1. The return year is a calendar year, and the salient feature is that the time of the return year is based on astronomers according to the solar system.

The rules of operation are calculated in advance, and the time of regression is the true solar time on the surface of the earth.

System. 2. The sidereal year adopts a clock time system. The difference between true solar time and horological time is one year.

This is called precession. <>

Third, the trajectory of the movement is different.

1. The star year of the Epistle Hall is based on a fixed point on the celestial sphere (such as a distant star) as a reference.

The period of motion is the revolution of the earth.

The average period.

2. The return year is the time interval between the solar center passing through the vernal equinox (or autumn equinox, winter solstice or summer solstice) twice in a row on the ecliptic, that is, the sun shines directly on the Tropic of Cancer twice in a row.

or Tropic of Capricorn). Therefore, the return year is also known as the "solar year" and "seasonal year".

1. The metering system is different.

The tropical year, also known as the solar year, belongs to the solar time measurement system and is the time experienced by the Sun's flat yellow longitude change of 360°. The sidereal year, which belongs to the sidereal time measurement system, is the time experienced by the Sun's apparent position on the ecliptic that is 360° different from the star's relative position.

2. The length of time is different.

In the year 2000, the average length of the return year (i.e. the flat return year) was si day. In the year 2000, the average length of a sidereal year (i.e. a flat year of a circle) was si-day.

The sidereal year is 20 minutes and seconds longer than the return year, which is due to the precession of the Earth's axis of rotation.

3. The calculation time is different.

The return year is based on the vernal equinox, and the time when the sun travels one week from the vernal equinox and returns to the vernal equinox is the vernal equinox year. Sidereal year: The time elapsed by the Earth relative to a distant star in orbit around the Sun 360°.

The reference points for the year of return are the stars and the equinox. The return year, also known as the solar year, refers to the time interval between the two consecutive passes of the vernal equinox by the mean 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. The return year is a four-season cycle, which is the same as the bright and blind sidereal year, and the reason why they are different in time is that the different time systems adopted by the earth shorten the time of the return year.

The reference points for the year of return are the stars and the equinox. The return year, also known as the solar year, refers to the time interval between the two consecutive passes of the vernal equinox by the mean 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. The return year is a cycle of the four seasons, the same as the sidereal year, and the reverence is also the earth's orbital cycle, and the reason why they are different in time is that the different time systems adopted by the gods are used, and the different rotations of the earth shorten the time of the return year.

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.

It is difficult to have **, just to explain why the swing of the earth's axis will cause the spring equinox to move westward is difficult enough, you must have a good spatial thinking ability.

Because of the rotation of the earth itself, it is a gyroscope, and the inherent characteristic of the gyroscope is that its axis will oscillate slowly, which is called "gyroscope precession". And this kind of oscillation of the earth's axis has a proper noun, called "precession".

Because of the precession, the intersection of the equator and the ecliptic is not fixed, but moves westward every year, and the ascending node of the two intersections of the equatorial ecliptic is the vernal equinox. The return year is the cycle in which the sun reaches the vernal equinox twice.

Because the vernal equinox moves westward, and the sun travels from west to east on the ecliptic in the background of the starry sky, that is, the sun does not have to travel 360 degrees on the ecliptic to meet the vernal equinox again and complete a return year, so the 360 sidereal year will be longer than the return year.

The return year is the time when the vernal equinox is the starting point and then returning to the vernal equinox, because the receding of the vernal equinox point will reduce the time of the spring equinox point every year, so the return year is short.