How the spring equinox marks the changing seasons


Brits may still be feeling the cold, but no longer as the first day of spring is fast approaching, marking the return of longer days, new flowers and warmer weather.

The March Equinox (called the Fall Equinox in the Southern Hemisphere) has long been celebrated as a time of rebirth in the Northern Hemisphere.

Spring festivals and holidays such as Easter and Passover are the primary celebrations in many cultures as the Sun’s path lines up with the Earth’s equator.

When is the first day of astronomical spring?

Astronomical seasons are determined by the tilt of the Earth as it revolves around the Sun. These seasons revolve around the equinoxes and the solstices.

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The vernal or spring equinox therefore marks the first day of astronomical spring; this year it falls on Saturday, March 20 in the northern hemisphere.

The season will continue until the summer solstice, which will take place on Monday, June 21, 2021.

Why is it called the “equinox” of spring?

Since night and day have almost exactly the same duration – 12 hours – all over the world, the event is called the equinox, which literally means “equal night” in Latin (equi – equal and nox – night).

In reality, however, the equinoxes do not have exactly 12 hours of daylight. The solstices and equinoxes mark key stages in the Earth’s astronomical cycle.

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In a year, there are two equinoxes (spring and autumn) and two solstices (summer and winter). This year’s fall equinox takes place on Tuesday, September 22.

The dates of the equinoxes and solstices are not fixed due to the Earth’s elliptical orbit of the Sun. They are the closest in January and the furthest in July (aphelia).

The equinox marks the changing of the seasons, as the balance of light changes to extend days or nights. Whether that means snowstorms or heat waves depends on the hemisphere.

It is also possible to see the Sun rise and set directly in the East and West, while it appears off-center at other times of the year.

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What happens at the equinox?

The Earth’s axis always tilts at an angle of about 23.5 ° to the ecliptic, that is, the imaginary plane created by the Earth’s orbit around the Sun.

On any other day of the year, the northern hemisphere or the southern hemisphere tilts a little towards the sun, but at both equinoxes, the tilt of the Earth’s axis is perpendicular to the sun’s rays. The equinox occurs at the exact moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north.



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