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axis of rotation
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Diagram showing Earth's axis of rotation tilted at about 23.5 degrees, illustrating precession as the axis traces a circular path over 26,000 years, shifting alignment from Polaris, the current North Star, to Vega. Labels indicate the plane of Earth's orbit and the changing orientation of the axis over time. A diagram illustrating rotation around a fixed axis, with a purple irregular object centered on three labeled axes (x, y, z) and a small orange mass rotating at a distance Ri from the z-axis at an angle theta.
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axis of rotation

physics and mathematics
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Diagram showing Earth's axis of rotation tilted at about 23.5 degrees, illustrating precession as the axis traces a circular path over 26,000 years, shifting alignment from Polaris, the current North Star, to Vega. Labels indicate the plane of Earth's orbit and the changing orientation of the axis over time.
Earth's axis of rotation Earth's axis of rotation itself rotates, or precesses, completing one circle every 26,000 years. Consequently, Earth's North Pole points toward different stars (and sometimes toward empty space) as it travels in this circle. This precession is so slow that it is not noticeable in a person's lifetime, though astronomers must consider its effect when studying ancient sites such as Stonehenge.

The axis of rotation is a fundamental concept in physics and mathematics, representing the straight line around which a rigid body moves in circles. This axis is fixed in space, and the body's resistance to rotational motion is known as rotational inertia.12

Key aspects include:
* Definition: The line through all fixed points of a rotating body, with all other points moving in circles around it.1
* Inertia: A body resists changes in its rotational motion, similar to how mass resists changes in linear motion.2
* Moment of Inertia: This quantity, denoted by I, expresses a body's rotational inertia and depends on how mass is distributed relative to the axis of rotation. Mass farther from the axis contributes more significantly to the moment of inertia.2
* Mathematical Representation: Angular momentum (L) is related to angular velocity (ω) by L = Iω, and torque (τ) is related to angular acceleration (α) by τ = Iα.2

The Earth, for example, completes one rotation around its axis approximately every 24 hours. In crystallography, a rotation axis refers to a symmetry element within a crystal structure.34

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4 Britannica Sources
  1. axis of rotation
  2. mechanics - Rotation about a fixed axis
  3. rotation axis
  4. rotations

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