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Axial parallelism

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Axial parallelism of the Earth

Axial parallelism is the characteristic of an orbiting body in which the direction of the axis remains parallel to itself throughout its orbit.

Examples

Earth's axial parallelism

Axial parallelism of the Earth is a primary reason for the seasons

The Earth's orbit, with its axis tilted at 23.5 degrees, exhibits approximate axial parallelism, maintaining its direction towards Polaris (the "North Star") year-round. Together with the Earth's axial tilt, this is one of the primary reasons for the Earth's seasons, as illustrated by the diagram to the right.[1][2][3][4][5]

Minor variation in the direction of the axis, known as axial precession, takes place over the course of 26,000 years. As a result, over the next 11,000 years the Earth's axis will move to point towards Vega instead of Polaris.[6]

Other

Axial parallelism of Saturn's rings, in a 17th century work by James Ferguson (Scottish astronomer)
Axial parallelism can be seen in the moon's orbital plane

Axial parallelism is widely observed in astronomy. For example, the rings of Saturn and the moon's orbital plane both show this characteristic. The axial parallelism of the moon's orbital plane is a key factor in the phenomenon of eclipses.

Explanation

Early gyroscopes were used to demonstrate the principle.[7] Prior to the invention of the gyroscope, it had been explained by scientists in various ways.[8] Early modern astronomer David Gregory, a contemporary of Isaac Newton, wrote:

To explain the Motion of the Celestial Bodies about their proper Axes, given in Position, and the Revolutions of them… If a Body be said to be moved about a given Axe, being in other respects not moved, that Axe is suppos'd to be unmov'd, and every point out of it to describe a Circle, to whose Plane the Axis is perpendicular. And for that reason, if a Body be carried along a line, and at the fame time be revolved about a given Axe; the Axe, in all the time of the Body's motion, will continue parallel to it self. Nor is any thing else required to preserve this Parallelism, than that no other Motion besides these two be impressed upon the Body; for if there be no other third Motion in it, its Axe will continue always parallel to the Right-line, to which it was once parallel.[9]

This gyroscopic effect is described in modern times as "gyroscopic stiffness" or "rigidity in space". The Newtonian mechanical explanation is known as the conservation of angular momentum.[10]

References

  1. ^ Petersen, J.; Sack, D.; Gabler, R.E. (2014). Fundamentals of Physical Geography. Cengage Learning. p. 18. ISBN 978-1-285-96971-8. Retrieved 2022-12-02.
  2. ^ Oliver, J.E. (2008). Encyclopedia of World Climatology. Encyclopedia of World Climatology. Springer Netherlands. p. 651. ISBN 978-1-4020-3264-6. Retrieved 2022-12-02.
  3. ^ Rohli, R.V.; Vega, A.J. (2011). Climatology. Jones & Bartlett Learning, LLC. p. 30. ISBN 978-1-4496-5591-4. Retrieved 2022-12-02.
  4. ^ Lerner, K. Lee; Lerner, Brenda Wilmoth (2003). World of earth science. Farmington Hills, MI: Thomson-Gale. p. 487. ISBN 0-7876-9332-4. OCLC 60695883. Although these distances seem counterintuitive to residents of the Northern Hemisphere who experience summer in July and winter in January—the seasons are not nearly as greatly affected by dis­ tance as they are by changes in solar illumination caused by the fact that Earth's polar axis is inclined 23.5 degrees from the per­ pendicular to the ecliptic (the plane of the solar system through or near which most of the planet's orbits travel) and because the Earth exhibits parallelism (currently toward Polaris, the North Star) as it revolves about the Sun. {{cite book}}: soft hyphen character in |quote= at position 193 (help)
  5. ^ Lerner, K. Lee; Lerner, Brenda Wilmoth (2003). World of earth science. Farmington Hills, MI: Thomson-Gale. p. 105 and 454. ISBN 0-7876-9332-4. OCLC 60695883. During revolution about the Sun, the earth's polar axis exhibits parallelism to Polaris (also known as the North Star). Although observing parallelism, the orientation of Earth's polar axis exhibits precession—a circular wobbling exhibited by gyroscopes—that results in a 28,000-year-long preces­ sional cycle. Currently, Earth's polar axis points roughly in the direction of Polaris (the North Star). As a result of precession, over the next 11,000 years, Earth's axis will precess or wobble so that it assumes an orientation toward the star Vega. {{cite book}}: soft hyphen character in |quote= at position 296 (help)
  6. ^ The Encyclopaedia Britannica: A Dictionary of Arts, Sciences and General Literature. R.S. Peale. 1890. p. 351. Retrieved 2022-12-02. Under the title of precession instruments, various pieces of apparatus, involving the gyroscope principle, have been in use for a number of years for illustrating the precession of the equinoxes, and the parallelism of the earth's axis as it revolves round the sun.
  7. ^ Ferguson, J. (1673). Astronomy Explained Upon Sir Isaac Newton's Principles ... A New Edition, Corrected. [With Plates.]. W. Strahan. p. 189. Retrieved 2022-12-02.
  8. ^ Gregory, D. (1715). The Elements of Astronomy, Physical and Geometrical. By David Gregory ... Done Into English, with Additions and Corrections. To which is Annex'd, Dr. Halley's Synopsis of the Astronomy of Comets . J. Nicholson ... sold. p. 59. Retrieved 2022-12-02.
  9. ^ Giordano, N. (2012). College Physics: Reasoning and Relationships. Cengage Learning. p. 299. ISBN 978-1-285-22534-0. Retrieved 2022-12-02.
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