We have a good time the September equinox as the primary day of autumn for the Northern Hemisphere, and first day of spring for the Southern Hemisphere.
What’s it? It’s a milestone in Earth’s orbit across the sun. At an equinox, the sun seems straight above Earth’s equator. On the September equinox, it’s crossing from north to south.
When is it? The September equinox will fall at 6:50 UTC (1:50 a.m. CDT) on September 23, 2023.
Notice: The identify equinox comes from the Latin aequus (equal) and nox (night time). On the equinox, days and nights are mentioned to be equal in size for everybody throughout the globe. And it’s true. They’re roughly equal.
Read more: Why aren’t day and night exactly equal on the equinox?
Earth’s tilt causes it
The earliest people spent extra time outdoors than we do. They used the sky as each a clock and a calendar. And so they might simply see that the sun’s path throughout the sky, the size of daylight and the placement of the dawn and sundown all shift in a daily method all year long.
The equinoxes and solstices occur as a result of Earth tilts on its axis by 23 1/2 degrees. Due to the Earth’s tilt, the Northern and Southern Hemispheres commerce locations in receiving the sun’s gentle and heat most straight. The solstices point out our best (or least) tilt towards the sun, in both hemisphere. The equinoxes fall halfway between the solstices.
And, certainly, Earth’s two hemispheres obtain the sun’s rays about equally round equinox time.
However Earth by no means stops transferring in orbit across the sun. And today of roughly equal daylight and night time will change shortly, as we transfer towards the December solstice.
Perhaps you’ve observed that the size of daylight modifications extra shortly from day to day across the equinoxes than across the time of the solstices?
An excellent day to search out due east and due west
The day of an equinox is an efficient day for locating the instructions due east and due west out of your favourite place to observe the sky. The sun rises due east and units due west on the equinoxes. It’s true irrespective of the place you reside on Earth. Why? As a result of all of us see the identical sky.
In all places on Earth, besides on the North and South Poles, you might have a due east and due west level in your horizon. And every level marks the intersection of your horizon with the celestial equator, the imaginary line above the true equator of the Earth.
On the equinoxes, the sun seems overhead at native solar midday as seen from Earth’s equator, because the illustration beneath reveals. The sun is on the celestial equator. The celestial equator intersects due east and due west for everybody across the globe. So the sun rises and units due east and due west on the equinox.
So go outdoors round sundown or dawn on the day of an equinox. And see the placement of the sun on the horizon with respect to acquainted landmarks. In the event you do that, you’ll be capable to use these landmarks to search out these cardinal instructions within the weeks and months forward, lengthy after Earth has moved on in its ceaseless orbit across the sun.
Indicators of the September equinox in nature
The indicators that summer time is gone – and winter is coming – are in every single place now, on the northern half of Earth’s globe. Within the Northern Hemisphere, daybreak comes later, and sundown earlier. Additionally, discover the arc of the sun throughout the sky. It’s shifting southward now. And birds and butterflies are migrating south, together with the trail of the sun.
The shorter days are bringing cooler climate. A chill is within the air. In New York Metropolis and different modern locations, some individuals have stopped carrying white. Creatures of the wild are placing on their winter coats.
Throughout us, timber and crops are ending this yr’s cycle of progress. Maybe they’re responding with superb autumn leaves, or a final burst of bloom earlier than winter comes.
Within the night time sky, Fomalhaut – our Autumn Star – is making its method throughout the heavens every night time.
September equinox photographs from EarthSky’s group
Backside line: The September equinox is right here! It’ll arrive at 06:50 UTC on September 23, 2023. The sun can be precisely above Earth’s equator, transferring from north to south. Autumn for the Northern Hemisphere. Spring for the Southern Hemisphere. Right here’s all you’ll want to know.
Read: Year’s fastest sunsets at equinox
