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The Seasons

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Insolation

Earth is tilted at an angle of about 23.5˚, so as it moves around the Sun, different parts of Earth receive different amounts of sunlight.

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Angle of Insolation - The angle at which sunlight hits Earth’s surface.

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The angle of insolation is the primary reason why different latitudes have temperature differences.

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  • At lower latitudes, the angle of insolation is higher, sunlight will be more intense, and the temperature will increase.

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  • At higher latitudes, the angle of insolation is lower, sunlight will be less intense, and the temperature will decrease.

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Note: The max angle of insolation is 90˚ (direct ray) when the Sun is at the Zenith. This can only happen between the tropics.

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Lower Temperatures

Higher Temperatures

Zenith (Direct)

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Why Do We Have Seasons?

There are two main reasons we have different seasons on Earth.

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Earth’s Tilt: Earth is tilted at an angle of about 23.5˚. This tilt causes different parts of Earth to receive more direct sunlight during different times of the year.

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Earth’s Revolution: As Earth orbits the Sun, the Sun appears higher or lower in the sky throughout the year, which changes the amount of sunlight that each hemisphere receives.

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Summer Solstice

Arctic Circle 66.5˚N

Tropic of Cancer 23.5˚N

Tropic of Capricorn 23.5˚S

Equator 0˚

Antarctic Circle 66.5˚S

Date

June 21st

Northern Axis Direction

Toward the Sun

Direct Rays (Zenith)

Tropic of Cancer 23.5˚ N

Orbit Position

Aphelion

Day Length

~14 Hours in NYS

Sunrise Direction

Northeast in NYS

Summer Solstice

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Fall (Autumnal) Equinox

Date

September 23rd

Axis Direction

Equidistant

Direct Rays (Zenith)

Equator 0˚

Day Length

12 Hours Everywhere on Earth

Sunrise Direction

Due East Everywhere on Earth

Fall Equinox

Arctic Circle 66.5˚N

Tropic of Cancer 23.5˚N

Tropic of Capricorn 23.5˚S

Equator 0˚

Antarctic Circle 66.5˚S

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Winter Solstice

Date

December 21st

Northern Axis Direction

Away from the Sun

Direct Rays (Zenith)

Tropic of Capricorn 23.5˚ S

Orbit Position

Perihelion

Day Length

~9 Hours in NYS

Sunrise Direction

Southeast in NYS

Winter Solstice

Arctic Circle 66.5˚N

Tropic of Cancer 23.5˚N

Tropic of Capricorn 23.5˚S

Equator 0˚

Antarctic Circle 66.5˚S

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Spring (Vernal) Equinox

Date

March 21st

Axis Direction

Equidistant

Direct Rays (Zenith)

Equator 0˚

Day Length

12 Hours Everywhere on Earth

Sunrise Direction

Due East Everywhere on Earth

Spring Equinox

Arctic Circle 66.5˚N

Tropic of Cancer 23.5˚N

Tropic of Capricorn 23.5˚S

Equator 0˚

Antarctic Circle 66.5˚S

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Top Down View of The Earth

The diagrams below show a top-down view of the Earth during each of different solstice and equinox days.

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Arctic Circle 66.5˚N

Arctic Circle 66.5˚N

Arctic Circle 66.5˚N

North Pole

North Pole

North Pole

Winter Solstice

Equinox Days

Summer Solstice

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All The Seasons Together!

Winter Solstice

Summer Solstice

Fall Equinox

Spring Equinox