Equinox 2020: When is meteorological autumn? When is the astronomical start of autumn?

The yearly seasons are divvied up between two solstices and two equinoxes. In layman terms, the autumnal and spring equinox mark the start of the two seasons in September and March respectively. Similarly, the summer and winter solstice in June and December mark the start of summer and winter.

What is the autumnal equinox?

As our planet races around the Sun, the North and South Poles tilt back-and-forth at a 23.5-degree angle.

When the North Pole is most tilted towards the Sun, we experience the summer solstice in the Northern Hemisphere.

At the same time, the Southern Hemisphere experiences winter as less sunlight directly falls on this half of the globe.

The opposite is true when the North Pole tilts away from the Sun – the winter solstice happens.

In between these two solstices, when the North and South Pole are perpendicular to the Sun, we experience an equinox.

According to the Royal Observatory Greenwich, the Northern and Southern Hemisphere are equally illuminated on these days.

And as a result, we experience roughly the same amount of daytime and nighttime.

The Observatory said: “It’s the moment at which the plane of Earth’s equator passes through the centre of the Sun’s disk, or the moment that the Sun passes the celestial equator.

“On these dates, there are approximately equal hours of daylight and darkness.”

When is the meteorological autumn?

On these dates, there are approximately equal hours of daylight and darkness

Royal Observatory Greenwich

There is some debate over when the seasons start.

Some believe the movements of the planet dictate then summer, autumn, spring and winter start.

But there is another school of thought, which suggests the equinoxes and solstices fall during their respective seasons.

The Royal Observatory said: “Astronomically, the four seasons centre around the equinoxes and solstices.

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“However, there is disagreement between those who see the equinox/solstice as the start of the season and those who hold that it represents the middle of the season.”

Meteorologists divide the seasons into three calendar months.

Using this method, autumn started on September 1 and will end on December 1, the start of winter.

Spring will then begin on March 1 and end on June 1, the first day of summer.

When is the astronomical autumn?

If we follow the seasons based on the planet’s movements, then autumn will start this year on the September equinox.

The equinox will peak this year on September 22, 2020, at 2.30pm BST, when viewed from London.

The winter solstice will then happen on December 21 at 10.02pm BST.

The spring equinox will fall on March 20 at 9.37am BST.

And the summer solstice will fall on June 20 at 10.43pm BST.

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