What Is Precession? Why Is It Important To Know?

Everyone assumes that the constellations are fixed, and that everything you see in the sky, especially the pole stars will be a permanent fixture. That is actually not the case!

 What is Precession?

It’s rather simple, Earth has an axial wobble as it spins. Have you ever spun a top? As the top is spinning, have you noticed that the poles of the top are never perfectly straight, the poles wobble. Now imagine that kind of a wobble on a planet with an approximate 24,000 mile circumference, spinning around 1,000 mph.

This isn’t a wobble that you notice during your lifetime, but as we dive further into this article, this wobble has been observed thanks to many millennia’s worth of observations and recordings of the sky by astronomers over the years. This wobble repeats every 26,000 years.

 Pole Stars Are Not Permanent!

We live at a time when the North Celestial Pole (NCP) is less than a degree from Polaris, so it makes it very easy to use it as a pole star as to the naked eye it never appears to move.

Just by looking at the two animations above, you can see that the Earth’s celestial poles gradually shift, and thus stars that have roles as pole stars only take on that job on a temporary basis. Eventually, the NCP will move away from Polaris and another star will take on the role.

This is a diagram of the cycle for the NCP, and what years the NCP will be at. Negative years are BC, and positive years are AD.

During the time of Ancient Egypt, the pole star was Thuban, a star in Draco. Polaris’ role as a pole star actually began shortly before the Middle Ages, and will have that role until after the 31st century AD.  After that, it’ll be another 20,000 years before Polaris becomes the North Star.

One interesting note is that 12,000 years from now, Vega will be the North Star, and because it’s one of the brightest stars at night, to northern stargazers, it will actually make the “north star – brightest star” myth come true during its tenure. Sirius, the true brightest star in the night sky, will have shifted further south and become almost exclusively a southern hemisphere attraction. 

Southern Constellations Shift Further North (and Vice Versa)

Orion is currently closer to the celestial equator in the sky, and is reasonably high in the midwinter sky from northern latitudes,  but in time it will gradually shift further south, and in 15,000 AD, Orion’s belt will be very low, and prominent stars below the belt won’t be visible above the horizon, unless you travel to the southern hemisphere!

On the flip side,  Crux – The Southern Cross, and stars like Alpha and Beta Centauri in Centaurus will gradually shift further north and become easily visible in mid northern latitudes.

The Precession Causes Your True Zodiac Signs To Shift!

We call it, “Precession of the Equinoxes.” The date of reference is Vernal Equinox or around March 21. When Babylonian astrologers assigned “star dates” in 500 BC, they based them off the position of the Sun and what constellation it was in front of, not knowing they would shift naturally. Back then, Vernal Equinox landed in Aries, but now it’s actually in Pisces – this means the Sun is in front of Pisces during Vernal Equinox.

Read this article to read more about it. I hate to tell you (no, I don’t actually), but your true zodiac sign  is most likely inaccurate, and you have Earth’s precession to blame! 

Summer Stars Will Become Winter Stars!

Northern stargazers always associate Orion’s Belt with the winter, and Scorpius during the Summer, but thanks to this precession, while the ecliptic will be the same, as the Sun keeps shifting its position on respective dates every year, that means eventually your Winter Stars will be visible in Summer and vice versa!

Can you imagine seeing Sagittarius and Scorpius higher in the sky during the winter months? Can you imagine Taurus, Gemeni, and Orion being lower in the southern sky during the evening on summer nights? In 12,000 years, that is the sky that viewers will be seeing!

It’s important to understand precession, as it illustrates and reminds us that what you see in the sky may seem permanent, but it really isn’t! Generations all separated millennia apart will see slightly different skies!

Don’t forget that the constellations as we see them today may look slightly different over 10,000 years from now! 

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