To measure time intervals, natural time units associated with astronomical phenomena are used. Time itself is divided into large and small intervals. The latter include seconds, minutes, hours and days: they are associated with the rotation of our Blue Planet around its axis. Large intervals of time are associated with the rotation of the planet around the Sun. The calculation of years is based on the tropical year - this is the time period during which the planet makes a complete revolution around the Sun from its position at the zenith above the tropics until the next same position. One tropical year is equal to 365 days, 5 hours and 48 minutes.
Julius Caesar in 45 BC introduced the Julian calendar, which had 365.25 days, which was eleven minutes longer than the tropical year. However, over time, a large time difference has accumulated. To remedy this, in the sixteenth century, Pope Gregory XIII introduced a different calendar that took into account the leap year. It eliminated the extra days that ran up according to the Julian calendar. The Gregorian calendar is still in use today, dividing time into years, months, weeks, and days.
Time points
To capture inhistory of any events, people needed a calendar. However, he needed a point of reference. In ancient Egypt, a unique calendar was created that counts the days of the year. All events taking place in the world that we date by any day and year, century, era, start from the same date (event) in the distant past. If this were not the case, then there would be confusion on Earth and people would not understand from what point exactly they should be counted: some now could have the year 7000, while other peoples could have the 1000th. Our era begins its countdown from the date of the birth of Christ. It is from this year that the countdown of years begins.
Tropical month
There are many concepts of time, and they are all different: there is local daily time, universal time, tropical year, tropical month and other time calculations.
The tropical month is determined by the Moon. By definition, this is the time interval during which the longitude of the moon increases by 360 degrees. A tropical month is 29.5 solar Earth days.
Even in ancient Babylon, astronomers followed the moon, its seven-day cycle. They saw all the changes taking place with the Earth's satellite. This is how weeks appeared, which became a real public historical property and are still used in counting time (we also have seven days in one week).
Tropical year
To measure longer periods of time, the tropical year is used. This is the length of time between two equal crossings of the Sun's celestial equator as it orbits. Tropical durationyears - 365, 2 solar days. However, this indicator is not constant: over the millennium, the duration changes by a couple of seconds.
The speed of movement along the orbit is also unstable. From March to September, the movement of the planet takes 186 days, and the second part of the orbital path takes 179 days. The repetition of the movement of our planet around the Sun is called the annual movement of the Earth, as a result of which there is a change in seasonality.
Other types of calculus
In addition to the tropical year, other systems have been developed for calculation, such as the earth year, consisting of 365 days, the lunar year - represented by twelve successive repetitions of the phases of the moon.
There is also such a thing as a sidereal year. This is the time interval for a complete revolution of a body around its central body or around the Sun or any other star. Our sidereal year is called the tropical year.
In astronomy there is a concept of the galactic year, which provides for the rotation of the Sun around the center of the Milky Way galaxy. This year takes 223-230 million years.
Earth year
The circulation of our planet around the star has several types of years: tropical year, draconian, stellar, anomalistic. Each of them has its own characteristics.
Anomalistic year is the time interval between a pair of consecutive points through which the Sun passes, passing along geocentric orbits. The anomalistic year is 365.23 solar days.
There is also such a thing as a draconian year. Herepresents the time interval between two successive passages of the star through the same part of the lunar orbit. The draconian year is 346.62 solar days.
Stellar year is the time corresponding to one revolution of the Sun in the sky relative to the fixed stars. This period takes 365.25 solar days.
On Earth, people are more accustomed to seeing the calendar year. On average, it is 365 days. It is based on rounded values for the tropical year. Those minutes and hours that are rounded up are included every four years in a leap year of 366 days. Such calculations help to avoid strong discrepancies in time and astronomical observations.
Tropical Year Counts
The tropical year begins its countdown from the selected point of ecliptic longitude and until the completion of the full cycle of the seasons and the return of the Sun to this very point. When performing calculations, the spring equinox is usually taken as the starting point. For accurate calculations, two planes are taken: the plane of the celestial equator and the plane of the ecliptic. These two lines have a point of intersection. When the Sun passes twice at this point, the year is considered to have passed.
If another point is taken as a reference point, then the tropical year will be different. This is due to the fact that there are many variations of the angular velocities of the luminary. In this form, those arc seconds that the star does not pass along the ecliptic in a tropical year will lead to time shifts, and gradually night and day will shift.
Mean tropical year
The duration of the solar year depends on the point of reference. Scientists did not immediately come to a unified method of counting time, although more and more they took the days of the equinox as a starting point. This is due to the fact that it was from this reference point that the measurement error was minimal.
The beginning of the tropical year may be slightly shifted, as planetary disturbances may occur during the passage of the Sun across the sky.
Throughout the history of observations, the tropical year has changed more than once. It has never been equal to 365 days, because it lasts longer: its duration is always 365 days and five hours, but minutes and seconds are always different.
Tropical Year Options
If the Earth moved smoothly in space, without disturbances, then the tropical year would always be a constant unit. However, this does not happen, and this period of time is always different: it is strongly influenced by perturbations in the orbital motion of the planet and nearby space bodies.
Scientists were able to identify the cyclical occurrence of disturbances equal to six minutes. They disappear from time to time. These indicators are taken into account when determining the annual cycle of the Earth.
Calendar year
As already mentioned, there are many varieties of time calculation. On Earth, the Gregorian calendar is used to calculate time. It has its own periodicity, equal to four hundred years. In each period, months, days and datesare repeated. The average for this calendar is 365.25 days, which is pretty much the same as a tropical year.
Ever since this calendar was used, the equinoxes have always remained in place, which helped in agriculture. Also, this type of calendar simplified the calculations of Easter and other church holidays.
According to scientists, the tropical year will be out of sync with the Gregorian calendar by three days, but this will not happen soon, but in eight thousand years.
So what is a tropical year and what is it equal to? We can say that this is the calculation of time to which we are accustomed. Our calendar is based on the tropical year, with 365 days and five hours. To keep our calendar in sync with the tropical year, one day is added every four years. This is a necessary measure, without which the temporal discrepancies would be large: in ten leap years, the year would have shifted by as much as forty days. However, this does not happen due to the introduction of a leap year into the calendar.
