Axial Precession

This is the third installment in my once-in-a-while newsletter, The Magical Universe. If you dig it, you can subscribe here!

Magical thing no. 3: Axial Precession!

I was reading about the star Vega recently, and I came across a sentence that sounded kind of strange. It said: “Vega was the northern pole star around 12,000 BCE and will be so again around the year 13,727.”

Huh. I thought “The North Star” was the north star. It’s called Polaris, that literally means “the pole star.” What could cause a star, whose position is so reliable that it has been used for navigation since Late Antiquity[link], to change its place?

Well, news to me, it turns out that while the earth is spinning on its axis like this:

It’s also doing THIS:


This movement is called Axial Precession, and it happens pretty slowly. Earth does one of these rotations every 26,000 years.  I know what you’re thinking, “Oh big whoop, another space thing is happening too slow to matter to me.” Well guess what, the implications of this are major…ly interesting.

To understand the impact this kind of movement has, we need to understand exactly how the seasons work. 

Relative to it’s rotation around the sun, the Earth’s axis is titled by 23.5 degrees. Like this: 

During Earth’s year-long journey around the sun, summer is determined by which hemisphere is angled toward the sun. In the image above, summer is in the northern hemisphere, as the sun’s rays are hitting the northern hemisphere directly. It’s winter in the southern hemisphere, because those sweet sweet heat rays are hitting it at an angle, making them indirect and less concentrated.

This is what a year looks like:

So the axis of the earth does a full procession every 26,000 years. That means the side of the earth that is nearest to the sun will be in the opposite position, at the same time of year, 13,000 years in the future. On July 1st, 15015, it will be the dead of winter in Toronto. 

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