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Why do we Why do we have have seasons? seasons? (The Science Queen Website) (The Science Queen Website)

Why do we have seasons? (The Science Queen Website)

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Page 1: Why do we have seasons? (The Science Queen Website)

Why do we Why do we have seasons?have seasons?

(The Science Queen Website)(The Science Queen Website)

Page 2: Why do we have seasons? (The Science Queen Website)

Earth’s rotationEarth’s rotation

• The Earth rotates on its The Earth rotates on its axis every 23 hours & 56 axis every 23 hours & 56 minutesminutes

• One day on Earth is one One day on Earth is one rotation of the Earth.rotation of the Earth.

• Day on Earth is when our Day on Earth is when our side of the Earth faces the side of the Earth faces the sun.sun.

• Night on Earth is when the Night on Earth is when the side of Earth we are on side of Earth we are on faces away from the sun.faces away from the sun.

• The Earth rotates on its The Earth rotates on its axis every 23 hours & 56 axis every 23 hours & 56 minutesminutes

• One day on Earth is one One day on Earth is one rotation of the Earth.rotation of the Earth.

• Day on Earth is when our Day on Earth is when our side of the Earth faces the side of the Earth faces the sun.sun.

• Night on Earth is when the Night on Earth is when the side of Earth we are on side of Earth we are on faces away from the sun.faces away from the sun.

Page 3: Why do we have seasons? (The Science Queen Website)

Earth’s revolutionEarth’s revolution

• It takes the Earth It takes the Earth 365 rotations to 365 rotations to travel or revolve travel or revolve around the Sun around the Sun once. once.

• This is a year.This is a year.

• It takes the Earth It takes the Earth 365 rotations to 365 rotations to travel or revolve travel or revolve around the Sun around the Sun once. once.

• This is a year.This is a year.

Page 4: Why do we have seasons? (The Science Queen Website)

Earth’s TiltEarth’s Tilt

• Seasons are not caused Seasons are not caused by how close the Earth by how close the Earth is to the sun. is to the sun.

• In fact, the Earth is In fact, the Earth is closest to the sun closest to the sun around January 3 and around January 3 and farthest away from the farthest away from the sun around July 4.sun around July 4.

• Seasons are not caused Seasons are not caused by how close the Earth by how close the Earth is to the sun. is to the sun.

• In fact, the Earth is In fact, the Earth is closest to the sun closest to the sun around January 3 and around January 3 and farthest away from the farthest away from the sun around July 4.sun around July 4.

Ellipse Ellipse

Page 5: Why do we have seasons? (The Science Queen Website)

Earth’s TiltEarth’s Tilt

• Seasons are the result of the 23.5° tilt of the Earth's axis.

• This tilting is why we have seasons.

• The number of daylight hours is greater for the hemisphere, that is tilted toward the Sun.

• Seasons are the result of the 23.5° tilt of the Earth's axis.

• This tilting is why we have seasons.

• The number of daylight hours is greater for the hemisphere, that is tilted toward the Sun.

Page 6: Why do we have seasons? (The Science Queen Website)

Seasons?Seasons?• Summer - the Sun's rays are hitting the Summer - the Sun's rays are hitting the

Earth at a direct angle - warmerEarth at a direct angle - warmer• Winter - the Sun's rays are hitting the Earth Winter - the Sun's rays are hitting the Earth

at a more extreme angle - coolerat a more extreme angle - cooler

• Summer - the Sun's rays are hitting the Summer - the Sun's rays are hitting the Earth at a direct angle - warmerEarth at a direct angle - warmer

• Winter - the Sun's rays are hitting the Earth Winter - the Sun's rays are hitting the Earth at a more extreme angle - coolerat a more extreme angle - cooler

Page 7: Why do we have seasons? (The Science Queen Website)

Seasons?Seasons?

• Summer - the Sun's rays are hitting the Summer - the Sun's rays are hitting the Earth at a direct angle – long daysEarth at a direct angle – long days

• Winter - the Sun's rays are hitting the Winter - the Sun's rays are hitting the Earth at a more extreme angle – short Earth at a more extreme angle – short daysdays

• Summer - the Sun's rays are hitting the Summer - the Sun's rays are hitting the Earth at a direct angle – long daysEarth at a direct angle – long days

• Winter - the Sun's rays are hitting the Winter - the Sun's rays are hitting the Earth at a more extreme angle – short Earth at a more extreme angle – short daysdays

Page 8: Why do we have seasons? (The Science Queen Website)

Seasons…in a nut shellSeasons…in a nut shell

Page 9: Why do we have seasons? (The Science Queen Website)

SolsticeSolsticeSolsticeSolstice• Solstice - the tilt of the Earth's axis is d directly Solstice - the tilt of the Earth's axis is d directly

toward or away from the Suntoward or away from the Sun• Winter solstice is the shortest day of the year. It Winter solstice is the shortest day of the year. It

occurs on December 21 (N. Hemi) and marks the occurs on December 21 (N. Hemi) and marks the beginning of winter.beginning of winter.

• The Summer Solstice is the longest day of the year. The Summer Solstice is the longest day of the year. It occurs on June 21 (N. Hemi) and marks the It occurs on June 21 (N. Hemi) and marks the beginning of summer. beginning of summer.

• Solstice - the tilt of the Earth's axis is d directly Solstice - the tilt of the Earth's axis is d directly toward or away from the Suntoward or away from the Sun

• Winter solstice is the shortest day of the year. It Winter solstice is the shortest day of the year. It occurs on December 21 (N. Hemi) and marks the occurs on December 21 (N. Hemi) and marks the beginning of winter.beginning of winter.

• The Summer Solstice is the longest day of the year. The Summer Solstice is the longest day of the year. It occurs on June 21 (N. Hemi) and marks the It occurs on June 21 (N. Hemi) and marks the beginning of summer. beginning of summer.

Tyrrhenian Sea and Solstice Sky Credit & Copyright: Danilo Pivato

Page 10: Why do we have seasons? (The Science Queen Website)

SOLSTICESOLSTICE

• The North Pole has a 24-The North Pole has a 24-hour nighthour night

• The South Pole has a 24-The South Pole has a 24-hour day.hour day.

• Sunlight strikes the earth Sunlight strikes the earth most directly at the Tropic of most directly at the Tropic of Capricorn.Capricorn.

• The North Pole has a 24-The North Pole has a 24-hour nighthour night

• The South Pole has a 24-The South Pole has a 24-hour day.hour day.

• Sunlight strikes the earth Sunlight strikes the earth most directly at the Tropic of most directly at the Tropic of Capricorn.Capricorn.

http://k12.ocs.ou.edu/teachers/reference/solstice.gif

Page 11: Why do we have seasons? (The Science Queen Website)

EquinoxEquinox

• The day lasts 12 hours The day lasts 12 hours and a night lasts 12 hours and a night lasts 12 hours at all latitudes.at all latitudes.

• Equinox literally means Equinox literally means "equal night"."equal night".

• Sunlight strikes the earth Sunlight strikes the earth most directly at the most directly at the equator. equator.

• The day lasts 12 hours The day lasts 12 hours and a night lasts 12 hours and a night lasts 12 hours at all latitudes.at all latitudes.

• Equinox literally means Equinox literally means "equal night"."equal night".

• Sunlight strikes the earth Sunlight strikes the earth most directly at the most directly at the equator. equator.

http://k12.ocs.ou.edu/teachers/reference/equinox.gif

Page 12: Why do we have seasons? (The Science Queen Website)

EquinoxEquinox

• This occurs twice a year. This occurs twice a year.

• The vernal (spring) The vernal (spring) equinox occurs March equinox occurs March 21 (N. Hemi).21 (N. Hemi).

• The autumnal (fall) The autumnal (fall) equinox occurs equinox occurs September 21 (N. Hemi)September 21 (N. Hemi)..

• This occurs twice a year. This occurs twice a year.

• The vernal (spring) The vernal (spring) equinox occurs March equinox occurs March 21 (N. Hemi).21 (N. Hemi).

• The autumnal (fall) The autumnal (fall) equinox occurs equinox occurs September 21 (N. Hemi)September 21 (N. Hemi)..

Page 13: Why do we have seasons? (The Science Queen Website)

The Earth's seasons are not The Earth's seasons are not caused by the differences in the caused by the differences in the

distance from the Sun distance from the Sun throughout the year.throughout the year.

Page 14: Why do we have seasons? (The Science Queen Website)

The seasons are the result The seasons are the result of the tilt of the of the tilt of the

Earth's axis.Earth's axis.

I know this is a repeat, but it is important I know this is a repeat, but it is important that you understand this idea. Many that you understand this idea. Many

Americans, including Harvard graduates, Americans, including Harvard graduates, do not know what causes seasons!do not know what causes seasons!

Page 15: Why do we have seasons? (The Science Queen Website)

ReviewReviewLook closely at where the Sun is hitting the Look closely at where the Sun is hitting the

Earth during each season:Earth during each season:

http://Search.Lycos.com/setup.asp?r=5&src=clear2&query=weather+savvy