Earth’s Orbit and Seasons

Earth’s Orbit

• Earth orbits the Sun.
• Takes one full year to complete its orbit.
• Earth rotates on its axis, tilted slightly like a spinning top.
• The tilt remains constant as Earth orbits the Sun.

Seasonal Changes

Winter in the Northern Hemisphere

• North Pole tips away from the Sun.
• Sunlight strikes at a shallow angle.
• Results in:
  • Cool winter weather.
  • Short days and long nights.

Transition to Spring

• As Earth orbits, it moves towards spring.
• Tilt is neither toward nor away from the Sun:
  • Day and night are of equal length.

Summer in the Northern Hemisphere

• North Pole tips toward the Sun.
• Sunlight strikes more directly, resulting in:
  • Warmer summer days.
  • Longer daylight hours.

Southern Hemisphere Seasons

• Opposite seasons:
  • When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere.

Impact of Seasons on Life

Primary Producers

• Plant life and photosynthesizers respond to seasonal changes.
• Known as primary producers; they depend on sunlight.
• Earth-orbiting satellites measure CO2 absorption by primary producers.

Seasonal Productivity

• Bright regions on maps indicate high CO2 absorption.
• Spring increases productivity:
  • Sunshine warms cold waters, leading to a surge in phytoplankton and microscopic photosynthesizers.
  • These form the base of the ocean food web.
• On land:
  • Forests become green in spring, brightening continents.
  • In winter, continents appear dark due to a lack of photosynthesis.