QUIZ REVIEW:
Changes in Day Length and Sunlight Angle
The changes in day length and the angle of incoming sunlight signal the annual progression of the seasons.
These changes are attributed to four primary characteristics of Earth in its relationship with the sun:
Orbit: Earth orbits around the sun, completing one revolution each year.
Rotation: Earth spins on its axis, completing one rotation each day.
Axial Tilt: The Earth's axis is tilted relative to its orbital plane, maintaining an inclination of 23.5 degrees from the vertical.
Polarity: The Earth's axis always points in the same direction relative to the stars, a characteristic known as polarity.
Key Dates and Equinoxes/Solstices
Four significant days mark the seasonal transitions:
March Equinox: Occurs around March 20.
June Solstice: Occurs around June 21.
September Equinox: Occurs around September 22.
December Solstice: Occurs around December 21.
In viewing an animation illustrating these changes:
Start on the March equinox.
The June solstice shows the North Pole leaning most directly toward the sun.
By the December solstice, the North Pole leans most directly away from the sun.
Fundamental Cause of Seasonal Change
The primary reason for the change of seasons is the latitude receiving vertical rays of the sun.
When again viewing the animation:
Observe the latitude receiving the vertical rays of the sun.
The Earth's inclination is consistent throughout the year.
On each of the four special days:
The sun's rays are perpendicular to the Earth's surface at varying latitudes.
The animation displays latitudes receiving vertical rays and the lengths of day across these latitudes.
Latitude and Sunlight
On the March Equinox:
The equator receives the vertical rays of the sun.
On the June Solstice:
The tropic of Cancer receives the vertical rays.
On the September Equinox:
The equator receives the vertical rays again.
On the December Solstice:
The tropic of Capricorn receives the vertical rays.
Day Length Variations
Day length changes based on latitude. Observations from the animation show:
The equator maintains equal day and night lengths throughout the year.
Other latitudes experience variations in day length.
The circle of illumination marks the dividing line between day and night, influencing day length at different latitudes.
On the March Equinox:
Equal day and night lengths across Earth.
As Earth moves to its June position:
Day length increases in the Northern Hemisphere and decreases in the Southern Hemisphere.
The June Solstice marks the longest day of the year in the Northern Hemisphere and the shortest in the Southern Hemisphere.
Following the September Equinox:
Day length is again equal worldwide.
On the December Solstice:
The Northern Hemisphere experiences the shortest day, while the Southern Hemisphere experiences the longest day.
Effects Near the North Pole
Observations from the North Pole show:
On the March Equinox:
The sun rises and remains above the horizon continuously for the subsequent six months.
Following the March Equinox:
The Arctic region with twenty-four hours of daylight expands weekly.
On the June Solstice:
Continuous daylight extends from the North Pole to the Arctic Circle.
After the June Solstice:
The period of continuous daylight decreases weekly until the September Equinox, when the sun sets at the North Pole and remains below the horizon for six months.
Following the September Equinox:
The region of continuous darkness increases weekly until the December Solstice,
When it extends from the North Pole to the Arctic Circle.
After the December Solstice:
The darkness decreases weekly until the March Equinox, when the sun once again rises at the North Pole.