Lecture on Spinning in the Universe

Introduction

• Everything is spinning: Earth, Sun, Solar System, Galaxy.
• Raises the question: Why is everything spinning?

Earth's Rotation

• Earth rotates around its axis at 1,040 miles per hour (465 m/s).
• Planets inherently rotate.

Formation of the Solar System

• 4.5 billion years ago: Solar system formed from helium and hydrogen clouds (nebula-like).
• Variations in density led to coalescing of gases, likely triggered by nearby supernova.
• As gravity increased, particles fell together and began to spin.

Direction of Spin

• Rotation is generally counter-clockwise, conserving angular momentum.
• Most celestial bodies, including Earth, Mars, and the Sun, rotate counterclockwise.
  • There is no 'up' in space, but counterclockwise is the common rotational direction.

Physics of Rotation

• As gases gravitate together, they form a "tossed pizza dough" shape (ball in the center, disc outward).
• This shape is prevalent due to the laws of physics.

Collapse and Fragmentation

• Interstellar clouds rotate, collapse, and fragment, forming suns, planets, and asteroids.
• Original gaseous angular momentum persists.
• Inertia maintains rotation over time.

Changes in Rotation

• Rotation slows over time. Example: Day will be 2 milliseconds longer in 100 years.
• Catastrophic events can alter rotation.
• Unique Cases:
  • Venus rotates clockwise; possibilities include axis flip or reversed rotation due to its atmosphere and proximity to the sun.
  • Uranus was knocked on its side, affecting its rotation.

Galactic Rotation

• Galaxies spin both clockwise and counterclockwise relative to Earth.
• Spiral galaxies often spin with arms trailing, but exceptions exist.
  • Example: Hubble spotted galaxy NGC 4622 with arms leading its rotation due to interaction with another galaxy.

Conservation of Energy

• Energy conservation is key; rotation persists unless disrupted.
• Analogy to figure skater: Faster spin with arms in, slower with arms out.

Conclusion

• Universe-wide spinning reflects basic physics principles.

Questions

• The lecture closes with a prompt for further scientific inquiry.