Natural Sciences


The equinox occurs when day and night have the same duration , thanks to the fact that the Sun is above the Equator at certain times of the year. If we drew this astronomical phenomenon, we could perfectly divide the earth into two halves, one with sunlight and the other completely at night. The word originates from the Latin aequinoctĭum , which means “equal night.”

The equinoxes should not be confused with the summer and winter solstices , which are a different phenomenon: it occurs on the longest day of the year and the shortest day, respectively. In many places, the solstice is better known than the equinox, since festivals and rituals are held, especially on the winter solstice, which occurs on December 21.

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Equinox facts and characteristics

Normally, the equinox occurs twice a year, between March 20 and 21 and September 22 and 23 . During this phenomenon, the Sun reaches its highest point in the sky at 90 ° to a person on the earth’s surface. This also means that, on that day, the parallel of declination of the Sun and the celestial equator concur.

Regardless of what happens outside our planet, for humans this event has a simple meaning: the spring and autumn seasons begin in the countries that maintain the climate seasons and according to the hemisphere where they are.

For example, in the northern hemisphere, the March equinox means that spring begins, and that of September, the autumn begins. On the other hand, in the southern hemisphere, the March equinox welcomes fall and the September equinox to spring.

Equinox characteristics:

  • The sun’s rays penetrate the intertropical zone with intensity , causing light and heat to reach the southern and northern hemispheres in the same way.
  • Unlike the solstice, the equinox lasts for a few days .
  • Although it does not always occur on the same day every year, because not all years are the same length, it can be determined when the next equinoxes will occur. For example, in 2021 it will occur on 03/20 and 09/22.

Examples of equinoxes

  • 2018: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/23.
  • 2019: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/23.
  • 2020: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/22.
  • 2022: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/23.
  • 2023: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/23.
  • 2025: Spring (north) and Autumn (south) 03/20. Autumn (north) and Spring (south) 09/22.

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