Earth-Sun Relationships #6 video lecture

Key Characteristic of Earth's Revolution

  • The Earth revolves around the sun in a slightly elliptical orbit rather than a perfect circle.

Scale Issues in Representation of Space

  • Space is so vast that true scale representations are unmanageable.
  • For context, if the sun is represented as a grapefruit, the nearest star would be thousands of miles away, making accurate diagrams impractical.

Earth’s Rotation

  • Rotation Direction: The Earth rotates on its axis from west to east.
    • Northern Hemisphere: Spins counterclockwise.
    • Southern Hemisphere: Spins clockwise.

Distance to the Sun

  • Average distance to the Sun is often quoted as 93 million miles, but this distance varies due to the elliptical orbit.
    • The Earth gets as close as 91.5 million miles (perihelion) and as far as 94.5 million miles (aphelion).
  • **Terminology:
    • Perihelion:** Closest distance to the Sun, occurring in January.
    • Aphelion: Farthest distance from the Sun, occurring on July 4th.

Seasons and Earth-Sun Relationship

  • Seasons: Incorrectly perceived by many to be linked to Earth’s distance from the sun.
    • In reality, it is axial tilt and orientation that define seasons, not the distance.
  • Example: In the Southern Hemisphere, July 4th is winter, while it's summer in the Northern Hemisphere.

Characteristics of Earth’s Orbit

  1. Elliptical Orbit: The first key characteristic.
    • Defined by Kepler’s laws.
  2. Plane of the Ecliptic: The plane in which the Earth orbits the sun, approximately flat over the course of the year.
  3. Angle of Inclination: The axis is tilted at 66.5 degrees from the plane of the ecliptic and this angle is constant throughout the year.
  4. Constant Axial Orientation: The Earth’s axial tilt does not change direction throughout the year.
    • It currently points toward the North Star (Polaris).

Finding Polaris

  • Polaris is located at the end of the Little Dipper, and it serves as a guide for navigation in the Northern Hemisphere.
  • Finding Polaris: Use the Big Dipper's pointer stars to locate it.

Conclusion

  • Understanding Earth's revolution involves recognizing its elliptical orbit, axial tilt, and how these factors contribute to seasonal changes and navigation.
  • Memorizing key terms such as perihelion, aphelion, angle of inclination, and the significance of Polaris for location and navigation is crucial for comprehension in geography and astronomy courses.