Earth is a cosmic object involved in the continuous movement of the universe. It rotates around its axis, travels millions of kilometers in an orbit around the Sun, along with the entire planetary system, slowly goes around the center of the Milky Way galaxy. The first two movements of the Earth are clearly noticeable to its inhabitants by the change in daily and seasonal illumination, changes in temperature, and the characteristics of the seasons. Today, in the focus of our attention are the characteristics and period of the Earth's revolution around the Sun, its influence on the life of the planet.
General information
Our planet is moving in a third orbit far from the star. On average, 149.5 million kilometers separate the Earth from the Sun. The length of the orbit is approximately 940 million km. The planet overcomes this distance in 365 days and 6 hours (one stellar or sidereal year is the period of the Earth's revolution around the Sun relative to distant bodies). Its speed during its movement in orbit reaches an average of 30 km / s.
For the earth observer, the revolution of the planet around the star is expressed in a change in the position of the sun in the sky. It moves one degree per day eastward with respect to the stars.
The orbit of planet Earth
The trajectory of our planet is not an ideal circle. It is an ellipse with the Sun in one of its tricks. This form of the orbit “forces” the Earth to either approach the star or move away from it. The point at which the distance from the planet to the Sun is minimal is called perihelion. Aphelion is a part of the orbit where the Earth is as far from the star. Nowadays, the first point is reached by the planet around January 3, and the second on July 4. At the same time, the Earth does not move around the Sun at a constant speed: after passing the aphelion, it accelerates and slows down, overcoming perihelion.
The minimum distance separating the two space bodies in January is 147 million km, the maximum - 152 million km.
Satellite
Together with the Earth, the Moon moves around the Sun. When observed from the north pole, the satellite moves counterclockwise. The orbit of the Earth and the orbit of the moon lie in different planes. The angle between them is approximately 5º. This mismatch significantly reduces the number of lunar and solar eclipses. If the planes of the orbits were identical, then one of these phenomena would occur once every two weeks.
The orbit of the Earth and the orbit of the moon are arranged in such a way that both objects rotate around a common center of mass with a period of about 27.3 days. At the same time, the tidal forces of the satellite gradually slow down the movement of our planet around its axis, thereby slightly increasing the length of the day.
Effects
The axis of our planet is not perpendicular to the plane of its orbit. This slope, as well as movement around the luminary, leads to certain changes in the climate throughout the year. The sun rises above the territory of our country at a time when the north pole of the planet is tilted to it. The day is getting longer, the temperature is rising. When the north pole deviates from the luminosity, cooling is replaced by cooling. Similar climate changes are also characteristic of the southern hemisphere.
The seasons change at the equinox and solstice, characterizing a certain position of the earth's axis relative to the orbit. Let us dwell on this in more detail.
The longest and shortest day
The solstice is a moment in time when the planetary axis is most inclined towards the star or in the opposite direction. The orbit of the Earth's movement around the Sun has two such sections. In mid-latitudes, the point at which the sun shines at noon rises higher with each passing day. This continues until the summer solstice, which falls on June 21 in the northern hemisphere (the longest day). Then the place of the midday stay of the star begins to decline until December 21-22. These days in the northern hemisphere is the winter solstice. In the middle latitudes, the shortest day comes, and then it begins to arrive. In the southern hemisphere, the axis tilt is opposite, so the winter solstice falls here in June and the summer solstice in December.
Day equals night
The equinox is the moment when the axis of the planet becomes perpendicular to the plane of the orbit. At this time, the terminator, the border between the illuminated and the dark half, passes strictly at the poles, that is, day is equal to night. There are two such points in orbit. The vernal equinox falls on March 20, the autumn equinox - on September 23. These dates are valid for the northern hemisphere. In the south, like the solstices, the equinoxes change places: in March it is autumnal, and in September - spring.
Where is warmer?
The circular orbit of the Earth - its features in combination with the tilt of the axis - has another consequence. At that moment, when the planet passes closest to the Sun, the south pole is looking in its direction. In the corresponding hemisphere, summer is at this time. The planet at the time of passage of perihelion receives 6.9% more energy than when it overcomes aphelion. This difference is precisely in the southern hemisphere. During the year, it receives a little more solar heat than the north. However, this difference is insignificant, since a significant part of the "additional" energy falls on the water expanses of the southern hemisphere and is absorbed by them.
Tropical and sidereal year
The period of the Earth's revolution around the Sun relative to the stars, as already mentioned, is approximately 365 days 6 hours 9 minutes. This is a sidereal year. It is logical to assume that the change of seasons fits into this segment. However, this is not entirely true: the time of the Earth's revolution around the Sun does not coincide with the full period of the seasons. It is the so-called tropical year, lasting 365 days 5 hours and 51 minutes. They measure it most often from one spring equinox to another. The reason for the twenty-minute difference between the duration of the two periods is the precession of the earth's axis.
Calendar year
For convenience, it is considered that there are 365 days in a year. The remaining six and a half hours are added up per day for four turns of the Earth around the Sun. To compensate for this and in order to prevent an increase in the difference between the calendar year and the sidereal year, an “additional” day is introduced, February 29th.
The only satellite of the Earth, the moon, has some influence on this process. It is expressed, as noted earlier, in slowing down the rotation of the planet. Every hundred years, the length of the day increases by about one thousandth.
Gregorian calendar
The usual account of the day was introduced in 1582. The Gregorian calendar , unlike the Julian one, for a long time allows the “civil” year to correspond to the full cycle of season changes. According to it, every four hundred years, months, days of the week and dates are exactly repeated. By duration, the year in the Gregorian calendar is very close to the tropical.
The reform was aimed at returning the vernal equinox to its usual place - on March 21. The fact is that from the first century AD to the sixteenth, the real date, when the day is equal to night, moved to March 10. The main motivation for revising the calendar was the need to correctly calculate Easter Day. For this, it was important to keep March 21 as a day close to the real equinox. The Gregorian calendar copes with this task very well. A shift in the date of the vernal equinox by one day will occur no earlier than in 10,000 years.
If we compare the calendar and tropical years, then more significant changes are possible here. As a result of the peculiarities of the Earth’s movement and the factors influencing it, in about 3200 years a discrepancy will accumulate with a one-day change of seasons. If at this time it will be important to maintain the approximate equality of the tropical and calendar years, then reform will again be required, similar to that which was carried out in the 16th century.
The period of the Earth's revolution around the Sun, thus, correlates with the concepts of a calendar, sidereal and tropical year. Methods for determining their duration have been improved since antiquity. New data on the interaction of objects in outer space allow us to make assumptions about the relevance of the modern understanding of the term “year” in two, three, or even ten thousand years. The time of the Earth's revolution around the Sun and its connection with the change of seasons and calendar is a good example of the influence of global astronomical processes on human social life, as well as the dependencies of individual elements within the global system of the Universe.