The Southern Hemisphere (SH) passed the autumn equinox at 1:30 am of the day March 20, 2016, the GMT. At the same time, the Northern Hemisphere (NH) passed the spring equinox.
The equinoxes (autumn and spring) and the solstices (summer and winter) are specific moments with day, month, hour and second accurate. It is not a period. So it is not correct to say “entered the solstice.” You can say we (the idea of a moment) the summer solstice (winter) and enter (the idea of a period that will extend) in the fall (spring).
What is equinox?
the word “equinox” ( aequinoctium ) comes from the Latin aequus (equal) and nox (night): equal nights. The day of the equinox is the day of the year when the number of sun hours is equal to the number of hours without sun or night. The day and night are the month number of hours. As we move to the middle of the year, for the winter, the nights get longer and shorter days. In summer it is the opposite: long and short nights days
Have you noticed that the date of the change of the seasons or falls on the same day one year to the next? In 2015 and 2016 the fall in HS, and spring in HN, began on 20 March. But in other years may be on the 19th until the 21st.
Curiosity
The sun rises exactly in the cardinal east point only twice a year on the day of the equinox of autumn and spring.
Why occur seasons?
the seasons occur because gradient central axis of the Earth. This axis makes an angle of 23.5 ° relative to the line of the Sun plan.
The date and time of the beginning and end of the seasons is a mathematical calculation made by astronomers and not by meteorologists. It is possible to know the date and time of the start of the seasons with many years in advance. But time and the weather did not meet the astronomical calculations. Not always the most intense cold occurs in the dead of winter and not always the strongest heat is in the summer.
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