Autumn Equinox: 8 things to know about the first day of autumn

The autumn equinox is upon us: on Saturday, September 22, the northern and southern hemispheres will experience a fair amount of light. For those of us in the northern hemisphere, it marks the beginning of autumn and the daylight hours continue to shorten until the winter solstice in December. For those south of the equator, it's the beginning of spring.

Technically speaking, the equinox occurs when the sun is directly in line with the equator. This will happen at 9:54 pm Eastern time Saturday.

Below you will find a short scientific guide on the most equal night of the season.

1) Why do we have equinoxes?

The autumn and spring equinoxes, the seasons, and the changing hours of daylight throughout the year are all due to one fact: the Earth rotates on an inclined axis.

The tilt – probably caused by a massive object that hit the Earth billions of years ago – means that for half of the year, the North Pole is directed to the sun (like in the picture below). For the other half of the year, the South Pole receives more light. That's why we have seasons.

The NASA

Here is an accelerated demonstration of the phenomenon that has occurred throughout the year from space. In the video, you can see how the line separating the day of the night oscillates between the poles of the year.

NASA / Meteosat / Robert Simmon

And here's another cool way to visualize the seasons. In 2013, a resident of Alberta, Canada, took this pinhole photo of the sun course throughout the year and shared it with the EarthSky astronomy website. You can see the dramatic change of the sun's arc from December to June.

(You can easily create a similar image at home.All you need is a box, photo paper, duct tape and pin instructions here.)

2) How many hours of day will I have on Saturday?

The equinox literally means "equal night". And during the equinox, most places on Earth will see about 12 hours of day and 12 hours of night.

But not all places will know exactly the same amount of daylight. For example, Saturday, Fairbanks, Alaska, will see 12 hours and 16 minutes of daylight. Key West, Florida, will see 12 hours and 7 minutes. The differences are due to the refraction of sunlight (curved) when it enters the Earth's atmosphere at different latitudes.

You may notice that both of these locations have hours of clarity greater than 12 hours. Are not the day and the night equal? The time of day is slightly longer than the night on the equinox because of the way we measure the length of a day: from the first indication of the sun above the day to day. horizon until the last survey before it falls below the horizon. evening. As the sun is slow to get up and go to bed, it adds a few extra minutes of day.

Check out TimeAndDate.com for the number of hours of sunshine you will get during the equinox.

3) Can I really balance an egg only at its end during the equinox?

AFP / Getty Images

You may have been told, as a child, that at the equinox, it is easier to balance an egg vertically on a flat surface than other days of the year.

The practice was born in China as a tradition on the first day of spring in the Chinese lunar calendar, early February. According to the South China Morning Post, "The theory says that at this time of year, the moon and the earth are exactly in alignment, the celestial bodies generating the perfect balance of forces needed to make it possible".

It's a myth. The amount of light we receive during the day has no power over the gravitational pull of Earth or our ability to balance things. You can balance an egg at the end of each day of the year (if you are well balanced).

4) When do the leaves start to change color?

Karen Bleier / AFP / Getty Images

As days start to shorten, deciduous (green-leaved) trees signal their leaves to stop producing chlorophyll, the green pigment responsible for leaf color and photosynthesis.

According to the National Arboretum of the United States, as color change is more dependent on light than temperature, it occurs at virtually the same time, year after year.

Temperature and weather conditions may, however, affect the intensity of fall colors and their lifespan. They can also subtly affect when the leaves begin to change. And drought can change the speed at which leaves turn. For example, the drought in Maine has made the trees in the state turn orange a bit early.

Because of all the variables involved, it can be difficult to accurately predict when fall colors will peak and how long they will last in a particular area. But here's an admirable effort: The SmokyMountains.com site (a tourism promotion site in Smoky Mountains) has created this interactive map (click on the link to play with) to determine fall colors by county.

5) What is actually in "pumpkin spice"?

"Pumpkin Spice" is not a spice but a mix of spices. And it does not contain pumpkin.

This Epicurious recipe includes cinnamon, ginger, allspice, nutmeg and cloves. It's fall.

6) Is there an old monument that is doing something fresh during the equinox?

During the winter and summer solstices, crowds flock to Stonehenge in the UK. During the solstices, the sun rises or sets according to the layout of the 5,000-year-old monument. And while some people come to Stonehenge for the fall equinox, the real place is Mexico.

This is because on the equinox, the pyramid of Chichen Itza, on the Yucatan peninsula, presents a wonderful spectacle. Built by the Maya about 1,000 years ago, the pyramid is designed to project a shadow on the equinox highlighting the body of Kukulkan, a feathered serpent god. A snake-headed statue is located at the bottom of the pyramid, and at sunset on the day of the equinox, sunlight and shadow show the snake's body joining the head.

It's easier to see in a video. Check it below.

7) Are there equinoxes on other planets?

Yes! All the planets of our solar system turn on an inclined axis and therefore have seasons. Some of these inclinations are minor (such as mercury, which is inclined at 2.11 degrees). But others look more like the Earth (23.5 degrees) or are even more extreme (Uranus is tilted at 98 degrees!).

Below, a beautiful composite image of Saturn on its equinox captured by the Cassini spacecraft (RIP) in 2009. The gas giant is tilted 27 degrees from the sun and the equinoxes on the planet are less frequent than on Earth. Saturn sees an equinox about once every 15 years (because it takes Saturn 29 years to complete an orbit around the sun).

Cassini Imaging / NASA team

During Saturn's equinox, his rings become unusually dark. This is because these rings are only about 30 feet thick, and when light hits them, there is not much surface to think about.

8) I clicked on this article accidentally and I just want a breathtaking image of the sun

Observatory of Solar Dynamics, NASA

The image above was taken by NASA's Solar Dynamics Observatory, a spacecraft launched in 2010 to better understand the sun.

Last summer, NASA launched the Parker solar probe, a spacecraft that will arrive within 4 million kilometers of the sun's surface (much closer than any other spacecraft before). The objective is to study the atmosphere, the weather and the magnetism of the sun and to understand why the solar corona (its atmosphere) is much hotter than its surface. Yet even at several million kilometers, the probe will have to withstand temperatures of 2500 degrees Fahrenheit.

It's essential to understand the sun: Brad Plumer wrote for Vox about what happens when the sun breaks and sends weather to our space to wreak havoc on Earth.