Equinox

see also: Etymology of Equinox

The equinoxes of March and September are the two moments of the year when the Jour and the Nuit are roughly of the same duration. At the time of the equinoxes, the sun rises exactly to the Is and lie down exactly with the Western. In Astronomy, an equinox is the moment when the Sun reaches one of the two intersections between the ecliptic and the celestial equator: its variation is then null. The intersection corresponding to the equinox of March is the vernal Point .

Etymologiquement, the word equinox comes from Latin æquinoctium , of æquus “ égal ”, and Nox, noctis “ nuit ”.

One can be however astonished to note that the days preceding the vernal equinox see already a sunning higher than 12:00. However, the apparent Diameter of the sun (a little more than one half degree), which is visible the morning and the evening, as well as the Réfraction of the rays of the Sun in the atmosphere, lengthens the duration of the day of a little more than 5 minutes. The same phenomenon reproduces the days following the autumnal equinox.

In the two hemispheres, the vernal equinox marks the beginning of the Printemps and the autumnal equinox marks the beginning of the Automne: spring begins in March in the northern hemisphere and in September in the southern hemisphere. The equinox of March is also called vernal equinox (of Latin worm, veris “ printemps ”): it is the date where the Sun passes to the vernal Point. Also let us note that, at the time of the equinoxes, all the points of the Earth located on the same meridian line, north pole with the south pole, receive the sunlight during the day.

Dates of the equinox

The dates and hours of the equinoxes can be calculated on the site of IMCCE. Attention the hours indicated are in hours UTC. It is thus advisable to add the jet lag of your spindle (and the possible summer-time) to know the real date and the hour in your country.

For example, in 2011, the vernal equinox falls on March 20th, 2011 to 23:20 UTC. If one wants to know the date in a French calendar, it is necessary to add one hour (UTC+1 in winter) and thus it is on March 21st with 0:00 20 qu ' it will begin. It will be one March 21st and not a March 20th as announced by calculation. The same question arises for the majority of the dates of the majority of the astronomical sites.

But the equinoxes (as well as the solstices) are astronomical phenomena independent of the observers and there is interesting to notice, expressed in hours UTC or UT to remain universal, the variations of the date of the equinoxes in the calendar year since the creation of the Gregorian calendar (1582). This variation is caused by the difference in duration between the calendar year (365 or 366 days) and the Tropical year (approximately 365,2422 days).

The vernal equinox falls the 19,20 or March 21st. To, it always fell the 20 or on March 21st. Into the past, it fell on March 19th, 15 time in second half of the 17th century and 5 times at the end of the 18th century. It will fall on March 19th in 2044 again. To the 21e century, it will fall on March 21st only in 2003 and 2007. It will have to be awaited 2102, so that it falls down one March 21st. The autumnal equinox falls the 21,22,23 or September 24th. It in general falls the 22 or on September 23rd. It will fall on September 21st in 2092 and it will be the first time since the creation of the Gregorian calendar. That will reproduce in 2096, then it will be necessary to wait year 2464 so that it falls on September 21st again. It fell one September 24th, 2 time to the whole beginning the 19th century and 8 times at the beginning of the 20th century; it will fall again on this date into 2303 and it will be the last time.

See too

Simple: Equinox

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