what are equinoxes ?
Answers
- The equinox is defined as a day that occurs twice per year when the sun crosses the equator and the night and day are the same length. A day in March that is the beginning of spring and a day in September that is the beginning of fall.
- when the sun crosses the plane of the earth's equator, making night and day of approximately equal length all over the earth and occurring about March 21 (vernal equinox, or spring equinox ) and September 22 (autumnal equinox )
- At the equinox, Earth's two hemispheres are receiving the sun's rays equally. Night and day are often said to be equal in length. In fact, the word equinox comes from the Latin aequus (equal) and nox (night).
...equinox
ˈईक्विनॉक्स्
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noun
plural noun: equinoxes
one of the two times in the year (around 20 March and 22 September) when the sun is above the imagined line round the centre of the earth (equator) and day and night are of equal length
वर्ष के वे दो अवसर (20 मार्च और 22 सितंबर के आसपास) जब सूर्य भूमध्य रेखा के ऊपर होता है और दिन और रात बराबर होते हैं; विषुव.....
An equinox is commonly regarded as the instant of time when the plane (extended indefinitely in all directions) of Earth's equator passes through the geometric center of the Sun's disk.[3][4] This occurs twice each year, around 20 March and 23 September. In other words, it is the moment at which the center of the visible Sun is directly above the equator.
The Sun at the moment of the March equinox in 2019, when the center of the solar disk contacts the celestial equator (the imaginary line on the celestial sphere above Earth's equator) from south to north.
The equinoxes are created by the 23.5 degrees tilt of the Earth's geographical (rotational) pole (as opposed to the magnetic pole). Observed from the Earth, the sun appears to climb and descend in the sky as the Earth completes its one-year orbit around the sun. From the equinox (the sun over the equator at 0 degrees tilt), the sun appears to rise (or descend) into the relevant hemisphere. The highest latitudes of the sun directly overhead are marked on the Earth by the two Tropics, Cancer and Capricorn, which therefore mark the middle points of the summer and the winter. These points are called the winter and summer solstices and are seen from Earth as the points when the sun is highest and lowest in the sky. The equinox is the middle point of the sun's position between the two solstices. The equinoxes therefore mark the middle point between the two solstices when the sun is directly above the Earth's equator, i.e. in neither hemisphere, ergo the beginning of the spring and the autumn seasons; and the point at which day and night are approximately equal. Those countries that use Daylight Saving Time will reset their clock about this time to compensate for the ever changing daylight time.
The word is derived from the Latin aequinoctium, from aequus (equal) and nox (genitive noctis) (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the Sun, atmospheric refraction, and the rapidly changing duration of the length of day that occurs at most latitudes around the equinoxes. Long before conceiving this equality, primitive equatorial cultures noted the day when the Sun rises due east and sets due west, and indeed this happens on the day closest to the astronomically defined event.
In the Northern Hemisphere, the March equinox is called the vernal or spring equinox while the September equinox is called the autumnal or fall equinox. In the Southern Hemisphere, the reverse is true. The dates slightly vary due to leap years and other factors.[5]
Since the Moon (and to a lesser extent the planets) causes Earth's orbit to slightly vary from a perfect ellipse, the equinox is officially defined by the Sun's more regular ecliptic longitude rather than by its declination. The instants of the equinoxes are currently defined to be when the apparent geocentric longitude of the Sun is 0° and 180°.[6]
The Sun on the equinox as seen from the site of Pizzo Vento, Fondachelli-Fantina,