The phrase explaining what the day of the equinox is implies at least a basic knowledge of astronomical terms, because the equinox itself is a phenomenon studied by this particular science.
Required knowledge of astronomical terms
Our luminary makes its movement along the ecliptic, which is, speaking in unscientific terms, 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 both of them are perpendicular to the axis of the world), is called an equinox. The terminator (this is also an astronomical concept that has nothing to do with Schwarzenegger) is a line that divides any celestial body into a part illuminated by the sun and into a "night" part. So, on the day of the equinox, it is this terminator that passes throughgeographic poles of the Earth and divides it into two equal semi-ellipses.
Characteristic of the name
The name itself contains the concept that on the day of the equinox, night and day are equal to each other. From a scientific point of view, the night is always a little shorter, and the sun rises and sets not exactly in the east and west, but a little to the north. But all the same, from childhood we know that June 22 is not only the day the war began and school graduation balls (this was the case in Soviet times), but also the day of the summer equinox. However, December 22 is also called the summer and winter solstices. This happens because the sun in these periods of time is either at the highest point above the horizon, or at the lowest, and farthest from the celestial equator. That is, on the day of the equinox, the light and dark parts of the day are almost equal to each other.
Number characteristic of the dates of the equinoxes and solstices
On the days of the solstices, one of them - either day or night - maximally exceeds the other. The equinoxes and solstices are also notable for the fact that they serve as the beginning of the seasons. These dates are very remarkable, and always one of the family members says that, they say, today is the longest or shortest day, or that today the day is equal to the night. And this distinguishes him from a series of consecutive days. Almost always, the date of these moments becomes the 22nd, but there are also leap years, and other moments and phenomena of astronomy that affect the date shift by the 21st or 23rd. The months of March, June, September and December are those that fallequinoxes and solstices.
Holidays that came from ancient times
Of course, they have been known since ancient times. Our ancestors observed them and connected their lives with these dates, dozens of witnesses will accept this. For the ancient Slavs, a certain holiday is associated with each of these days, and it usually lasts a week (Carols, Rusalia, Maslenitsa week). So, on the winter solstice, Kolyada falls, a holiday later timed to coincide with Christmas. Velikden, or Komoyeditsa, she is Shrovetide - these names mark the spring equinox, the birth of the young sun. From this day, the astrological solar year begins, and our luminary passes into the Northern Hemisphere from the Southern. Maybe that's why March 20 is the holiday of astrology. Kupala (other names are Ivan-day, Solstice), or summer confrontation, is a great summer holiday of the ancient Slavs, fanned by legends that glorified brave people who go that night to look for a fern flower. Ovsen-Tausen, the day of the autumn equinox, after which winter slowly begins to come into its own, and the nights become longer. Therefore, our ancestors in Svyatovit (another name) lit candles - the most beautiful was put in a place of honor.
Earth's Special Climate Zone
All these dates served as starting points for the start of certain activities necessary for life, whether seasonal farming, building or storing for the winter. Spring and autumn equinoxesThey are also characterized by the fact that the sun gives off its light and heat equally to both the Northern and Southern hemispheres, and its rays reach both poles. These days it is located above the territory of such a climatic zone of the Earth as the tropics (translated from Greek means a turning circle). In different directions from the equator to 23 and a few degrees, parallel to it are the northern and southern tropics. A characteristic feature of the area enclosed between them is that the Sun reaches its zenith above them twice a year - once on June 22 over the northern tropic, or the tropic of Cancer, the second time over the southern, or tropic of Capricorn. It happens on December 22nd. This is typical for all latitudes. North and south of the tropics at its zenith, the Sun never appears.
One of the consequences of the shift in the direction of the earth's axis
On the days of the equinox and solstice, it intersects with the celestial equator at points located in the constellations of Pisces (spring) and Virgo (autumn), and on the days of the greatest and least distance from the equator, that is, on the days of the summer and winter solstices, - in the constellations of Taurus and Sagittarius, respectively. The summer solstice moved from the zodiac constellation Gemini to Taurus 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 also shift. Spring dates differ from autumn dates, and if September falls on the 22nd-23rd, then the question “When is the day of springequinoxes? The answer will be: March 20th. It should be noted that for the Southern Hemisphere the dates will change places - autumn will become spring, because everything is the other way around there.
The role of the zodiac constellations
As noted above, the equinox points are the points of intersection of the celestial equator with the ecliptic, and they have their own zodiac symbols corresponding to the constellations in which they are located: spring - Aries, summer - Cancer, autumn - Libra, winter - Capricorn. It should be noted that the period of time between two equinoxes of the same name is called a tropical year, the number of solar days in which differs from the Julian calendar by approximately 6 hours. And only thanks to the leap year, which repeats once every 4 years, the date of the next equinox, running forward, 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 in such a way that even in the long term, the dates of the solstices and equinoxes fall on the same numbers. This happens because the Gregorian calendar provides for a 3-day skip once every 400 years.
One of the most important practical tasks of astronomy is to establish the date of the equinox
Dates vary from 1 to 2, no more than days. So how to determine for the coming years when the day of the equinox? It is noticed that as a result of the presence of small fluctuations, the earliest dates, thenis the 19th, falls on leap years. Naturally, the latest (22) falls directly on the preceding leap years. Very rarely there are earlier and later dates, the memory of them is kept for centuries. So, back in 1696, the spring equinox fell on March 19, and in 1903, the autumn equinox on September 24. Contemporaries will not see such deviations, because the 1696 record will be repeated in 2096, and the latest equinox (September 23) will occur no earlier than 2103. There are nuances associated with local time - the deviation in the figure from the world only happens when the exact date falls on 24:00. After all, to the west of the reference point - the zero meridian - a new day has not yet arrived.
