If Earth is tilted, why is Polaris always above the same spot?

  • Why is Polaris, the North Star, always above (or near) the North Pole? If Earth is tilted, Polaris' path should be in winter 23 degrees away from its path in summer, or not?


    Don't forget distance. Is the only point of difference as compared to the situation involving sun.

    I hope this doesn't confuse the issue, but it should be noted that Polaris isn't *precisely* in the same location, even over the course of a day. As wikipedia explains: "In 2018 Polaris is 0.66° away from the pole of rotation ... and so revolves around the pole in a small circle 1.3° in diameter." But we can imagine a "true" pole star that would be precisely still, in which case the question stands.

    Remember, the seasons are different in each hemisphere (they are caused by the hemisphere being faced more towards or away from the sun at different times during the orbit).

  • JohnHoltz

    JohnHoltz Correct answer

    3 years ago

    You are correct that the axis of the Earth's rotation is tilted with respect to the plane of its orbit by 23 degrees. But it is incorrect that the direction that the axis points changes by a large amount (it should be 2*23 degrees) over a 6 month time span.



    Incorrect orientation of axis



    Your assumption: If axis it pointed at Polaris at (1), then it should be pointed at a different star at (2).



    The axis remains pointed in the same direction throughout the entire year because the laws of physics are that the axis of a spinning object remains pointed in the same direction unless a torque acts on the body to change its orientation. There are torques acting on the Earth (namely the Sun and Moon), but it takes 13000 years to change the direction from "one way to the opposite way", not 6 months.



    Correct orientation of axis



    Correct: The orientation of the Earth's spin axis remains pointed at the same star throughout the year (ignoring the slow, 26000 year precession cycle).


    Thank you so much! Now I understand why the stars are seen on the same paths.

    And also to note that if the axis changed in only 6 months, we would be perpetually stuck in the same seasons.

    For further reading on the "ignoring" bit: over thousands of years the pole star *does* change; see axial precession.

    @gerrit interesting article on The Long Now about axial precession and the calendar installation at the Hoover Dam: http://blog.longnow.org/02019/01/29/the-26000-year-astronomical-monument-hidden-in-plain-sight/

    Give my regards to your graphic designer. Top notch work there.

    We would also for example not have *spring, summer, autumn and winter* if #1 was the case.

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Content dated before 7/24/2021 11:53 AM