Precession causing perihelion to happen later | Cosmology & Astronomy | Khan Academy | Summary and Q&A

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July 14, 2011
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Precession causing perihelion to happen later | Cosmology & Astronomy | Khan Academy

TL;DR

Precession changes the direction of Earth's axis of rotation over a 26,000-year period, while obliquity changes the tilt of Earth's axis over long periods of time, affecting the severity of the seasons.

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Questions & Answers

Q: What is the difference between precession and obliquity?

Precession refers to the change in the direction of Earth's axis of rotation over a 26,000-year cycle, while obliquity refers to the fluctuation of Earth's axial tilt between 22 and 24.5 degrees over tens of thousands of years.

Q: How does precession affect our calendar?

Precession causes a shift in the direction of our axis of rotation, resulting in changes in the position of the winter and summer solstices within our calendar. However, our calendar is still based on the maximum tilt towards or away from the sun, so the dates of the solstices remain the same.

Q: How does obliquity impact the severity of the seasons?

Obliquity affects the severity of the seasons as a greater tilt towards the sun leads to a larger disparity between summer and winter. When Earth is less tilted, the difference between the seasons is smaller.

Q: Is our calendar influenced by the exact point in space or the tilt towards or away from the sun?

Our calendar is based on the maximum tilt towards or away from the sun, not the exact point in space. The dates of the solstices remain the same, even though the perihelion (closest point to the sun) and aphelion (farthest point from the sun) change over time.

Summary & Key Takeaways

  • Precession changes the direction of Earth's axis of rotation over a long period of time, resulting in the shift of the winter and summer solstices within our calendar.

  • Obliquity, the tilt of Earth's axis, fluctuates between 22 and 24.5 degrees over tens of thousands of years, impacting the severity of the seasons.

  • Our calendar is based on the maximum tilt towards or away from the sun, rather than the exact point in space, causing shifts in the solstices over time.

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