Revolution and Earth's Orbit Around the Sun

Earth's Orbit Shape

• Earth travels around the Sun in an elliptical orbit, often described as almost a circle.
• Elliptical orbit: An oval path around the Sun.
• Sun's distance: Average distance is 93 million miles.
  • Closest (Perihelion): 91.5 million miles
  • Farthest (Aphelion): 94.5 million miles

Perihelion and Aphelion

• Perihelion: Closest to the Sun; occurs around January 3rd.
• Aphelion: Farthest from the Sun; occurs around July 4th.
• Seasons: Earth's proximity to the Sun does not cause the seasons.
  • Distance impact: Only a 2-3% difference in solar heat received.

Earth’s Yearly Orbit

• Year duration: 365.25 days (365 days and 6 hours).
• Leap Year: Every 4th year has an extra day (February 29) to account for the extra 6 hours annually.

Calendar and Months

• Roman origins of months:
  • March to June named after gods (Mars, Juno).
  • July and August named after emperors (Julius Caesar, Augustus Caesar).
  • September to December named numerically (7 to 10).
• Months' lengths: Based on moon's orbit (28 days), adjusted to fit the solar year.
  • Leads to months alternating between 30 and 31 days, with February being an exception.

Earth’s Axis and Plane of Ecliptic

• Plane of Ecliptic: Plane in which Earth and planets orbit the Sun.
• Earth's Axis Tilt: Tilted at 23.5 degrees relative to the ecliptic.
  • Causes variation in sun exposure and seasons.
• Polaris Alignment: Earth's axis points towards Polaris (North Star) continuously.

Parallelism of Earth's Axis

• Definition: Earth's axis maintains a constant direction throughout its orbit.
• Impact: Results in varying sun exposure between hemispheres, creating seasons.
  • Northern Hemisphere: Summer when sun's rays fall vertically.
  • Southern Hemisphere: Winter during the Northern Hemisphere's summer, and vice versa.

Reasons for Seasons

• Sun’s Rays: Vertical rays provide concentrated heat; oblique rays spread heat over a larger area.
• Tropic of Cancer and Capricorn: Key latitudes (23.5° N and S) for direct sun rays.
• Heat distribution: Major contributor to seasonal changes, not Earth's distance from the Sun.