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Autumnal equinox brings first day of fall to Earth's Northern Hemisphere

Google celebrated the 2021 autumn equinox with the release of this doodle of a spiky hedgehog awash in autumn colors.
Google celebrated the 2021 autumn equinox with the release of this doodle of a spiky hedgehog awash in autumn colors. (Image credit: Google)

September's equinox has arrived today, marking the beginning of astronomical autumn in the Northern Hemisphere and the first day of fall, where the nights will get longer than the days until the spring equinox in March 2022.

At 3:21 p.m. EDT (19:21 GMT) today, the planet will reach the exact point in its orbit when its axis doesn't appear tilted with respect to the sun, meaning the Northern and Southern Hemispheres receive an equal amount of sunshine during the 24-hour period within this day. 

For the rest of the year, the length of the day and night are unequal across the globe because the Earth's axis, tilted by 23.5 degrees with respect to the plane in which the planet orbits, is also tilted with respect to the sun. 

To celebrate this annual astronomical mark, Google released a doodle of a spiky hedgehog awash in autumn colors. 

Related: Asteroid three times the size of the Statue of Liberty zooms past Earth on fall equinox

As the planet completes its orbit around the star within the 365 (and a quarter) day period, the tilt of its axis, which leads from the North to the South Pole, brings seasonal changes to different parts of the globe. As those in the south welcome their summer season, the north plunges into the dark and cold winter months. 

But today, we are all equal, as all over the world the day will last exactly 12 hours. Observers located on the equator will see the sun exactly overhead at noon, travelling directly from north to south, according to NASA. For those located on the North Pole, today will be the last day they will see the sun's disc above the horizon until the spring equinox in March 2022.

For those of us in the Northern Hemisphere, the length of the night from now on will exceed the length of day. With shorter days, colder weather is set to arrive. For those in the Southern Hemisphere it will be the exact opposite. Days will be getting longer from now on ushering in the light and pleasant spring and summer seasons. 

Related: Twilight and the myths of the equinox and 6-month polar night

The next important astronomical mark, the winter solstice, will take place on Dec. 21. At 11:58 a.m. EST (1558 GMT), when the tilt of the Earth's axis with respect to the sun will result in the shortest day in the Northern Hemisphere. From then on, the length of the day in the Northern Hemisphere will slowly start to creep up, while in the Southern Hemisphere, the day will start getting shorter. 

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Tereza Pultarova

Tereza is a London-based science and technology journalist, aspiring fiction writer and amateur gymnast. Originally from Prague, the Czech Republic, she spent the first seven years of her career working as a reporter, script-writer and presenter for various TV programmes of the Czech Public Service Television. She later took a career break to pursue further education and added a Master's in Science from the International Space University, France, to her Bachelor's in Journalism and Master's in Cultural Anthropology from Prague's Charles University. She worked as a reporter at the Engineering and Technology magazine, freelanced for a range of publications including Live Science, Space.com, Professional Engineering, Via Satellite and Space News and served as a maternity cover science editor at the European Space Agency.