Today is the Start of Autumn and the Beginning of Longer Nights and Shorter Days

An Autumn days view

 

Are you excited for Autumn and Winter?

Meteorologists use a special biannual event called the equinox to mark the change in seasons. It occurs when the sun passes directly over the Earth’s equator and creates a day and night that are the same length.

The equinox happens on or around March 22 and on or around September 22 each year. In the southern hemisphere, the seasons are flipped and today’s equinox marks the start of longer days and shorter nights.

Why does the equinox happen?

Autumn Equinox

The Autumn Equinox is marked by a yearly celestial alignment

The equinox occurs because of the tilt of the Earth in relation to the sun. This is what causes the seasons.

The Earth’s tilt is 23.5 degrees relative to the plane of its orbit and means that, although one revolution of the planet takes 24 hours – it’s different depending on the time of year.

During the summer time, the Northern hemisphere is tilted towards the sun. So we get longer days as more light falls on this part of the surface.

In the winter time it’s the Southern hemisphere that gets the majority of the light.

Equinox Chart

“Equal night”

On the autumnal equinox, the Earth hits the turning point in its orbit where neither the North or the South poles are tilted towards the sun.

It means the amount of daylight and night time is the same at all points on the Earth’s surface.

The word equinox is Latin for “equal night”.

Meteorologists use it as the official turning point in the seasons because – although it can vary from year to year, it allows for the most accurate record-keeping.

It is celebrated around the world, notably at the Aztec monument Chichen Itza in Mexco.

During the equinox a sliver of light makes its way down the monument at sunset, drawing in crowds of onlookers.

Chichen Itza

What the experts say

“The Earth’s orbit is [only] about three percent out of round,” explains Jay Holberg, a senior research scientist at the lunar and planetary lab at the University of Arizona.

“So in the northern winter—in December—the sun is actually closest to the Earth by a small amount, and in the summer it’s actually farther away,” he told National Geographic .

Matthew Holman, an astrophysicist at Harvard University said: “The equinox is defined as the time of an event. It’s really not when the day and the night are of equal length,although that’s what we think of – it’s really that moment is when the sun is on the equator at local noon.”

Google doodle

Today’s Google Doodle celebrates the first day of autumn with the orange glow of autumn’s falling leaves.

In the doodle, a group of boulders watch as leaves are blown around in the breeze, before coming to rest on the ground.