Polaris Wasn’t Always the North Star: How Earth’s Wobble Shifts the Celestial Pole

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Polaris Wasn’t Always the North Star: How Earth’s Wobble Shifts the Celestial Pole

Polaris has been the constant guide for explorers and navigators in the northern hemisphere for thousands of years, hence its other name, the famous North Star. It is significant where it is located near the north rotational axis of Earth, and the whole sky appears to spin about it. But that’s not always been the case, and it won’t always be the case. The planet’s sluggish axial wobble, called precession, makes the pole trace a circle about every 26,000 years, bringing different stars into view over the ages.

How Earth’s 26,000-Year Axial Precession Shifts the North Star Over Time

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, gravitational forces from the sun and moon affect the rotation of Earth; these produce a bulge at the equator and axial precession. Every 26,000 years or so, this wobble makes a complete circle, and it makes the celestial pole move on a cycle, pointing to stars in sequence over time. Thuban, in the star constellation Draco, was the closest visible in the sky to the celestial pole some 4,700 years ago. The stars, such as Kochab and Pherkad, were the nearest to the pole about 3,000 years ago. Polaris now has the title, but not for very long.

The axis of the Earth will eventually change again, bringing new stars into prominence. In about 2,200 years, Errai in the constellation Cepheus will become the North Star. Alderamin, likewise in Cepheus, will have its turn some 5,000 years from now. Deneb, who will approach the pole once more about 9,800 CE, and Vega, a former pole star, returning in roughly 12,000 years, complete this cycle.
Many of these stars fit identifiable constellations, including Cepheus, Draco, and Ursa Minor. Modern stargazing apps incorporating augmented reality for

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navigation allow amateur astronomers to trace their positions.

As Polaris continues to shine overhead today, its reign is only temporary. Earth’s steady 26,000-year precessional cycle guarantees that other stars will eventually take its place, proving that even in the cosmos, change is constant.

 

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