The time when the center of the sun in its apparent motion along the ecliptic crosses the celestial equator is called the equinox. At this time, the Earth is in a position relative to the Sun, when both hemispheres, from the equator to the poles, heated relatively the same. This happens twice a year: the vernal equinox and the autumnal equinox.
The vernal equinox occurs when the Sun moves from the Southern Hemisphere sky in the north and this is usually 20 or 21 March. The autumnal equinox occurs on 22 or 23 September, when the Sun moves from the northern hemisphere to the southern. These days, for all places of the earth (excluding parts of the poles) day almost equal night.
The vernal equinox in the past decade fell to 21 March twice — in 2003 and 2007. In other years the vernal equinox occurred on March 20. In 2011, the vernal equinox occurs on March 21 at 02 hours 21 minutes Moscow time.
From the day of the vernal equinox seasons by hemispheres change in the Southern Hemisphere occurs astronomical autumn, and in the North — astronomical spring and continues until the day of the summer solstice (June 21). After the vernal equinox always comes already spring warmth, no matter how cold it was before.
On the day of the vernal equinox well known by the ancient scholars of China, India and Egypt. In ancient times, the vernal equinox, considered a great holiday.
In religion, in ancient times, the vernal equinox, also was given great importance. Date of Easter, which is celebrated every year at different times, measured from the vernal equinox as follows: March 21 — the first new moon — the first Sunday, and it was thought that the holiday.
It all began in the year 325 AD, when the Council of Nicaea, where the Julian calendar was adopted for the entire Christian world. By order of the Council of Nicaea, the equinox was obliged to "forever" falls on March 21, as it was in the year of the cathedral, but at the end of the XIV century. Christian church suddenly discovered that the vernal equinox has long been not the same as the 21 March, and more than that, every 128 years comes first for another day, and when the error notice, the difference was up to 10 days: the Julian calendar was the time of the equinox March 21 attack , but in reality it is advancing on March 11. This is indicated by many astronomers, and the clergy are not just going to reform, but each time it was delayed for various reasons.
In 1582, Pope Gregory XIII issued a special bull, on which days the expense has been moved forward by 10 days after Thursday and Friday October 4, 1582 presumes no 5 and October 15.
Training reform at the direction of Gregory XIII implemented astronomers Christopher Clavius and Luigi Lilio. The new calendar called the Pope was called Gregorian.
Many people saved the day of the vernal equinox as a holiday in the calendar. For example, in Persian it is called Nowruz, which means "new day". Rooted in the tradition of ancient farmers in the Middle East and Central Asia, the festival has become an integral part of the culture of many peoples professing Islam. In the CIS, it is celebrated as a national Tatars, Kazakhs, Bashkirs, Kyrgyz, Tajiks, Uzbeks, and many other nations. In some countries, declared a national holiday Nowruz and holiday.
In Japan, the vernal equinox is called Syumbun no Hi. It is celebrated on March 21, and in leap years on March 20. Another name for the holiday — Tunit, which means "average day." This name is associated with the fact that the spring equinox is in the middle of the week, called Higan, which means "the other side".
At this time the Japanese visit the graves of their deceased relatives, as in Japanese gardens blooming sakura, this portends the coming of spring.
In Russia most of all rejoice that the daylight hours will be added by the minute, and the long-awaited summer.