(CNN) — Twice a year, everyone on Earth is seemingly on equal footing — at least when it comes to the distribution of light and dark.
But during equinoxes, everyone from pole to pole gets to enjoy a 12 / 12 split of day and night. Well, there’s just one rub — it isn’t as perfectly “equal” as you may have thought.
There’s a good explanation (SCIENCE!) for why you don’t get precisely 12 hours of daylight on the equinox. More on that farther down in the article.
Here are the answers to your fall equinox questions:
Where does the word ‘equinox’ come from?
Precisely when does the fall equinox happen?
Why does fall equinox happen?
The Earth rotates along an imaginary line that runs from North Pole to South Pole. It’s called the axis, and this rotation is what gives us day and night.
The effect is at its maximum in late June and late December. Those are the solstices, and they have the most extreme differences between day and night, especially near the poles. (That’s why it stays light for so long each day during the summer in places such as Scandinavia and Alaska.)
But since the summer solstice three months ago in June, you’ve noticed that our days have been progressively becoming shorter in the Northern Hemisphere and the nights longer. And now here we are at the fall equinox!
What did our ancestors know about all this?
A ‘superhenge’ discovered near Stonehenge in England is believed to have been built 4,500 years ago. CNN’s Erin McLaughlin reports.
Here are just a few of the sites associated with the equinox:
What are some festivals, myths and rituals still with us?
All around the world, the fall equinox has weaved its way into our cultures and traditions.
Great Britain’s beloved harvest festivals have their roots in fall equinox since pagan times.
Autumn leaves put on a show at Showa Kinen Park in Tokyo.
courtesy Takashi Hososhima, creative commons
Are the Northern Lights really more active at the equinoxes?
Yes — they often put on more of a show this time of year.
It turns out the autumnal equinox and spring (or vernal equinox) usually coincide with peak activity with the aurora borealis.
So why isn’t the equinox exactly equal?
It turns out you actually get a little more daylight than darkness on the equinox, depending on where you are on the planet. How does that happen? The answer is a bit complicated but fascinating.
This bending of light rays “causes the sun to appear above the horizon when the actual position of the sun is below the horizon.” The day is a bit longer at higher latitudes than at the equator because it takes the sun longer to rise and set the closer you get to the poles.
So on fall equinox, the length of day will vary a little depending on where you are. Here are a few breakdowns to give you an idea:
— At the equator: About 12 hours and 6 and half minutes (Quito, Ecuador; Nairobi, Kenya; and Singapore are all close to the equator)
— At 30 degrees latitude: About 12 hours and 8 minutes (Houston, Texas; Cairo, Egypt; and Shanghai, China)
— At 60 degrees latitude: About 12 hours and 16 minutes (Helsinki, Finland, and Anchorage, Alaska)