Spring and autumn equinox

The phrase explaining what is the day of the equinox, implies at least an elementary knowledge of astronomical terms, because the equinox itself is a phenomenon studied by this science.

Necessary knowledge of astronomical terms

Our luminary makes its movement along the ecliptic, which is, in a non-scientific language, the plane of the earth's orbit. And the moment when the sun, making its way along the ecliptic, crosses the celestial equator, which is a large circle of air and airless space, parallel to the earth's equator (their planes coincide, and they are both perpendicular to the axis of the world), is called the equinox. Terminator (this is also an astronomical concept, which has nothing to do with Schwarzenegger) is a line that divides any celestial body into a sunlit part and a "night" one. So, on the day of the equinox, this terminator passes through the geographic poles of the Earth and divides it into two equal half-ellipses.

A characteristic feature of the name

In the name itself lies the notion that on the day of the equinox, night and day are equal among themselves. Scientifically, the night is always a little shorter, and the sun rises and sits not exactly exactly in the east and west, but slightly to the north. But all the same, from childhood we know that June 22 is not only the day of the beginning of the war and school graduation balls (as was the case in Soviet times), but also the day of the summer equinox. However, December 22 is also called the days of the summer and winter solstice. This happens because the sun in these periods of time is either at the highest point above the horizon, or at the lowest, and most distant from the celestial equator. That is, on the day of the equinox, the light and dark parts of the day are practically equal.

The number characteristic of the dates of the equinoxes and solstices

In the days of the solstices, one of them, either day or night, as much as possible exceeds the other. The days of the equinox and solstice are noteworthy also because they serve as the beginning of the seasons. Very noteworthy are these dates, and always one of the family members says that, they say, today is the longest or shortest day, or that today is the day equal to the night. And this distinguishes him from the succession of days that follow one another. Almost always the date of these moments is 22, but there are leap years, and other moments and phenomena of astronomy that affect the shift of the date by 21 or 23. Months March, June, September and December are those on which the days of the equinox and solstice fall.

Holidays that came from ancient times

Of course, they are known since ancient times. Our ancestors observed them and connected their lives with these dates, dozens of witnesses will take it. The ancient Slavs have a certain holiday associated with each of these days, and it lasts, as a rule, for a week (Christmas carols, Rusal, Shrovetide week). So, for the winter solstice there is Kolyada, a holiday later timed to Christmas. Velikden, or Komoditsa, she is Maslenitsa - these names signify the spring equinox, the birth of a young sun. From this day begins the astrological solar year, and our luminary passes into the Northern Hemisphere from the South. Maybe, therefore, on March 20, there is a celebration of astrology. Kupala (other names are Ivan-day, Solntsevorot), or summer confrontation, is a great summer feast of the ancient Slavs, fanned by legends, glorifying the brave people going this night to look for the flower of the fern. Ovsien-Tausen, the day of the autumnal equinox, after which the winter slowly begins to enter into its rights, and the nights grow longer. Therefore, our ancestors in Svyatovit (another name) lit candles - the most beautiful was put on the place of honor.

The special climatic zone of the Earth

All these dates served as reference points for the commencement of certain activities necessary for life - seasonal farming, construction or winter stocks. The days of the spring and autumn equinox are also characterized by the fact that the sun gives its light and heat to both the Northern and Southern Hemispheres equally, and its rays reach both poles. These days it is above the territory of such a climatic zone of the Earth as the tropics (in translation from Greek means a turning circle). In different directions from the equator to 23 with a small degree, parallel to it are the northern and southern tropics. A characteristic feature of the area between them is that over them twice a year the sun reaches the zenith - once on June 22 over the northern tropic, or the tropic of Cancer, the second time - over the South, or the tropic of Capricorn. This happens on December 22. This is typical for all latitudes. North and south of the tropics at the zenith, the sun does not ever exist.

One consequence of the displacement of the direction of the earth's axis

In the days of the equinox and the solstice, it intersects with the celestial equator at the points in the constellations of the Pisces (spring) and the Virgin (autumn), and in the days of the largest and smallest distance from the equator, that is, in the days of the summer and winter solstice, in the constellations of Taurus and Sagittarius respectively. From the zodiacal constellation Gemini in Taurus, the point of the summer solstice moved in 1988. Under the influence of the attraction of the Sun and the Moon, the earth's axis slowly shifts its direction (precession is another astronomical term), as a result of which the points of intersection of the star with the celestial equator are displaced. Spring dates differ from autumn numbers, and if September falls on 22-23th, then the question "When is the day of the vernal equinox?" Will be answered on March 20. It must be stipulated that the dates for the Southern Hemisphere will be reversed - the fall will be spring, because there everything is vice versa.

The role of the zodiacal constellations

As mentioned above, the equinox points are the points of intersection of the celestial equator with the ecliptic, and they have their own zodiacal symbols corresponding to the constellations in which are found: spring - Aries, summer - Cancer, autumn - Libra, winter - Capricorn. It should be noted that the time interval between the two identical equinoxes is called a tropical year, the amount of sunny days in which differs from the Julian calendar by approximately 6 hours. And only thanks to the leap year, which repeats once in 4 years, the date of the next equinox, which is running ahead, returns to the previous number. With the Gregorian year the difference is negligible (tropical - 365.2422 days, Gregorian - 365.2425), because this modern calendar is arranged so that even in the long run, the dates of solstices and equinoxes fall on the same numbers. This is because the Gregorian calendar provides for a pass of 3 days once in 400 years.

One of the most important practical tasks of astronomy is to establish the date of the equinox

The dates range from 1 to 2, not more than, days. So how to determine the coming years, when the equinox day? It is noticed that as a result of the presence of small fluctuations, the earliest dates, that is, the 19th, occur in leap years. Naturally, the latest (22) fall directly to the previous ones by a leap one. Very rarely there are earlier and later dates, the memory of them is stored in the centuries. So, in the distant 1696 the vernal equinox happened on March 19, and in 1903 - the autumnal on September 24. Such deviations will not be seen by contemporaries, because the recurrence of the 1696 record will be in 2096, and at the very least the equinox (September 23) will happen no earlier than 2103. There are nuances associated with local time - deviation in the figure from the world happens only when the exact date falls at 24:00. After all, west of the point of reference - the zero meridian - a new day has not yet come.