What is the spring equinox, which occurs this Saturday (23)?

This Saturday (23) the spring equinox takes place in the southern hemisphere of planet Earth, marking the end of winter and the beginning of spring, which began at 3:49 am.

The phenomenon also occurs in the northern hemisphere, but there, the date is called the autumnal equinox and opens the season of the same name.

At the equinoxes, which occur twice a year, day and night are exactly the same length: 12 hours each.

The phenomenon cannot be clearly perceived in regions close to the Equator which, in theory, already have 12-hour days and nights throughout the year.

However, the closer to the poles, in places like northern Canada, Norway and Russia, the duration of sunlight and darkness are equal on this day.

Precisely for this reason it is called equinox, a term that comes from the Latin word equinoxiumwhich means equality between day and night.

Why does the spring equinox occur?

The Earth rotates along an imaginary line that goes from the North pole to the South pole. It’s called the axis, and this rotation is what gives us day and night.

The axis is tilted 23.5 degrees, which causes one hemisphere of the planet to receive more sunlight than the other during half the year’s orbit around the Sun. This discrepancy in sunlight is what triggers the seasons.

The effect is maximum at the end of June and the end of December, when the solstices are experienced, when the time differences between day and night are greatest, especially near the poles.

Differences between day and night

Even at the equinox, there are small differences between light and dark perceived by people depending on where they are.

The “almost” equal hours of day and night are due to the complex way of measuring sunrise and the refraction of sunlight in our atmosphere. For example:

• In Ecuador: about 12 hours and 6 minutes (Quito, Nairobi, and Singapore are all close to the Equator);
• At 30 degrees latitude: about 12 hours and 8 minutes (Houston, Cairo and Shanghai);
• At 60 degrees latitude: about 12 hours and 16 minutes (Helsinki and Anchorage).

To get true equality between day and night, you have to wait days or even weeks after the official equinox. This day is called equilux and when it occurs depends on your latitude.

*With information from Forrest Brown, CNN Spanish

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