Hi Everybody!!
Spring officially arrived today right on time. In real time it is March 20, which is the vernal equinox. Below I have shared info from Wikipedia about the Equinox. You can also hit Google Search Button to discover more in this category. (The Google Search is also decorated in a cute growing Spring Doodle!) Your photostudy is of the new blooms around the grounds. Last night, the frogs began singing on the creek. It is amazing every year how new life springs forth everywhere with no "Permission" from Man!
Enjoy!

http://en.wikipedia.org/wiki/Equinox

Equinox

From Wikipedia, the free encyclopedia

An equinox occurs twice a year, around 20 March and 22 September. The word itself has several related definitions. The oldest meaning is the day whendaytime and night are of approximately equal duration.^[2] The word equinoxcomes from this definition, derived from the Latin aequus (equal) and nox (night). The equinox is not exactly the same as the day when period of daytime and night are of equal length for two reasons. Firstly, sunrise, which begins daytime, occurs when the top of the Sun's disk rises above the eastern horizon. At thatinstant, the disk's center is still below the horizon. Secondly, Earth's atmosphere refracts sunlight. As a result, an observer sees daylight before the first glimpse of the Sun's disk above the horizon. To avoid this ambiguity, the word equilux is sometimes used to mean a day on which the periods of daylight and night are equal.^[3]^{[note 1]} Times of sunset and sunrise vary with an observer's location (longitude and latitude), so the dates when day and night are of exactly equal length likewise depend on location.

The other definitions are based on several related simultaneous astronomicalevents, and refer either to the events themselves or to the days on which they occur. These events are the reason that the period of daytime and night are approximately equal on the day of a solstice.

An equinox occurs when when the plane of Earth's Equator passes the center of the Sun. At that instant, the tilt of Earth's axisneither inclines away from nor towards the Sun. The two annual equinoxes are the only times when the subsolar point—the place on Earth's surface where the center of the Sun is exactly overhead—is on the Equator, and, conversely, the Sun is at zenith over the Equator. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox.

At an equinox, the Sun is at one of the two opposite points on the celestial sphere where the celestial equator(i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: classically, the vernal point (RA = 00^h 00^m 00^s and longitude = 0º) and the autumnal point (RA = 12^h 00^m 00^s and longitude = 180º).

The equinoxes are the only times when the solar terminator is perpendicular to the Equator. As a result, the Northern and Southern Hemispheres are illuminated equally.

File:Earth-lighting-equinox EN.png

From Wikipedia, the free encyclopedia

During an equinox, the Earth's North and South poles are not tilted toward or away from the Sun, and the duration of daylight is theoretically the same at all points on Earth's surface.

Date

When Julius Caesar established his calendar in 45 BC he set 25 March as the spring equinox. Because a Julian year (365.25 days) is slightly longer than an actual year the calendar drifted with respect to the equinox, such that the equinox was occurring on about 21 March in AD 300 and by AD 1500 it had reached 11 March.

This drift induced Pope Gregory XIII to create a modern Gregorian calendar. The Pope wanted to restore the edicts concerning thedate of Easter of the Council of Nicaea of AD 325. (Incidentally, the date of Easter itself is fixed by an approximation of lunar cycles used in the Hebraic calendar, but according to the historian Bede the English name "Easter" comes from a pagan celebration by the Germanic tribes of the vernal (spring) equinox.) So the shift in the date of the equinox that occurred between the 4th and the 16th centuries was annulled with the Gregorian calendar, but nothing was done for the first four centuries of the Julian calendar. The days of 29 February of the years AD 100, AD 200, AD 300, and the day created by the irregular application of leap years between the assassination of Caesar and the decree of Augustus re-arranging the calendar in AD 8, remained in effect. This moved the equinox four days earlier than in Caesar's time.

Names

Vernal equinox and autumnal equinox: these classical names are direct derivatives of Latin (ver = spring and autumnus =autumn). These names are based on the seasons, and can be ambiguous since seasons of the northern hemisphere andsouthern hemisphere are opposites, and the vernal equinox of one hemisphere is the autumnal equinox of the other.
Spring equinox and fall equinox or autumn equinox: these are more colloquial names based on the seasons, and are also therefore ambiguous across hemispheres.
March equinox and September equinox: names referring to the times of the year when such equinoxes occur. These are without the ambiguity as to which hemisphere is the context, but are still not universal as not all people use a solar-based calendar where the equinoxes occur every year in the same month (as they do not in the Islamic calendar and Hebrew calendar, for example), and the names are not useful for other planets (Mars, for example), even though these planets do have seasons.
Northward equinox and southward equinox: names referring to the apparent motion of the Sun at the times of the equinox. The least culturally biased terms.
Vernal point and autumnal point are the points on the celestial sphere where the Sun is located on the vernal equinox andautumnal equinox respectively. Usually this terminology is fixed for the Northern hemisphere.
First point (or cusp) of Aries and first point of Libra are names formerly used by astronomers and now used by navigators and astrologers. Navigational ephemeris tables record the geographic position of the First Point of Aries as the reference for position of navigational stars. Due to the precession of the equinoxes, the astrological signs of the tropical zodiac where these equinoxes are located no longer correspond with the actual constellations once ascribed to them. The equinoxes are currently in the constellations of Pisces and Virgo. In sidereal astrology (notably Hindu astrology), by contrast, the first point of Aries remains aligned with Ras Hammel "the head of the ram", i.e. the Aries constellation.

Length of equinoctial day and night

Contour plot of the hours of daylight as a function of latitude and day of the year, showing approximately 12 hours of daylight at all latitudes during the equinoxes

On the day of the equinox, the center of the Sun spends a roughly equal amount of time above and below the horizon at every location on the Earth, so night and day are about the same length. The word equinox derives from the Latin words aequus (equal) and nox (night). In reality, the day is longer than the night at an equinox. Day is usually defined as the period when sunlight reaches the ground in the absence of local obstacles. From the Earth, the Sun appears as a disc rather than a point of light, so when the center of the Sun is below the horizon, its upper edge is visible. Furthermore, the atmosphere refracts light, so even when the upper limb of the Sun is 0.4 degrees below the horizon, its rays curve over the horizon to the ground. In sunrise/sunset tables, the assumed semidiameter (apparentradius) of the Sun is 16 minutes of arc and the atmospheric refraction is assumed to be 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon, its center is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects make the day about 14 minutes longer than the night at the Equator and longer still towards the Poles. The real equality of day and night only happens in places far enough from the Equator to have a seasonal difference in day length of at least 7 minutes, actually occurring a few days towards the winter side of each equinox.