Seasons Notes

Seasons on Earth

1. Reasons for seasons 

1. Earth’s axis is tilted 23.5 degrees from vertical 

1. The axis always points in the same direction 

2. 1st one hemisphere, & then the other is tipped toward the sun

1. Hemisphere tipped toward sun has longer periods of daylight, more direct sunlight, thus experiences summer 

2. Hemisphere tipped away from sun has winter, due to shorter days and less direct sunlight 

      3.   Areas near the equator do not have seasons 

1. No great changes in daylight periods or angle of sunlight 

June 20 -- Sun directly overhead 23.5° N, Tropic of Cancer

• First day of Summer in the Northern Hemisphere (NH), Summer Solstice

• Longest day of the year in the NH

• First day of Winter in the Southern Hemisphere (SH)

• Shortest day of the year in the SH

• Within the arctic circle (north pole) - 24 hours of light on this day only

• Within the Antarctic circle (south pole) - 24 hours of dark on this day only

• Length of daylight begins to decrease in the North

• Length of daylight begins to increase in the South

September 22

• Sun directly overhead the equator 

• Fall Equinox or Autumnal Equinox\

• First day of Fall in the Northern Hemisphere (NH)

• First day of Spring in the Southern Hemisphere (SH)

• Spring → “Vernal” Equinox

• Equal day and night everywhere - 12 hours of light and 12 hours of dark everywhere on the planet

December 21

• Sun directly overhead, 23.5° South - Tropic of Capricorn

• See June 20, switch hemispheres - everything is the same just switch hemispheres

• Shortest day

March 20

• See September 22nd, switch hemispheres - everything is the same just switch hemispheres

• NH's first day of spring