Earth Video

Why do we have seasons?

Seasons

• What are our seasons like?

• What are seasons like in other parts of the world?

• What do you think causes the seasons?

• What are our seasons like?

• What are seasons like in other parts of the world?

• What do you think causes the seasons?

Vocabulary• Axis: the angle between an object's

rotational axis, and a line perpendicular to its orbital plane.

• Tilt: moving into a sloping position

• Seasons: Each of the four divisions of the year (spring, summer, autumn, and winter) marked by particular weather patterns and daylight hours, resulting from the earth's changing position with regard to the sun

• Axis: the angle between an object's rotational axis, and a line perpendicular to its orbital plane.

• Tilt: moving into a sloping position

• Seasons: Each of the four divisions of the year (spring, summer, autumn, and winter) marked by particular weather patterns and daylight hours, resulting from the earth's changing position with regard to the sun

Vocabulary• Summer Solstice: marks the onset of

summer, at the time of the longest day, about June 21 in the northern hemisphere and December 22 in the southern hemisphere

• Winter Solstice: marks the onset of winter, at the time of the shortest day, about December 22 in the northern hemisphere and June 21 in the southern hemisphere

• Summer Solstice: marks the onset of summer, at the time of the longest day, about June 21 in the northern hemisphere and December 22 in the southern hemisphere

• Winter Solstice: marks the onset of winter, at the time of the shortest day, about December 22 in the northern hemisphere and June 21 in the southern hemisphere

Vocabulary• Equinox: occurs twice a year, when the tilt

of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator

• Examples of Equinoxes: Spring and Autumn Equinox

• Equinox: occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator

• Examples of Equinoxes: Spring and Autumn Equinox

Earth’s rotation

• The Earth rotates on its axis (imaginary vertical line around which Earth spins) every 23 hours & 56 minutes.

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

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

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

• The Earth rotates on its axis (imaginary vertical line around which Earth spins) every 23 hours & 56 minutes.

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

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

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

Earth’s revolution

• It takes the Earth 365 days (or rotations) to travel or revolve around the Earth once.

• This is called a year.

• It takes the Earth 365 days (or rotations) to travel or revolve around the Earth once.

• This is called a year.

Why do we have seasons?• The Earth’s orbit

around the sun is NOT a perfect circle. It is an ellipse.

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

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

• The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse.

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

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

Ellipse

Why do we have seasons?• Seasons are the result of the

tilt of the Earth's axis.

• Earth’s axis is tilted 23.5°.

• This tilting is why we have SEASONS like fall, winter, spring, summer.

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

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

• Earth’s axis is tilted 23.5°.

• This tilting is why we have SEASONS like fall, winter, spring, summer.

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

Why do we have seasons?• Summer is warmer than winter (in each

hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter

• Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter

Turn Out The Lights

Why do we have seasons?

• Also the days are much longer than the nights during the summer.

• During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

• Also the days are much longer than the nights during the summer.

• During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

Seasons…in a nut shell

SolsticesSolstices• Solstices occur twice a year, when the tilt of the Earth's

axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.

• Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.

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

• Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.

• Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.

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

SOLSTICE

• During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours.

• During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.

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

• During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours.

• During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.

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

Equinoxes

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

• Equinox literally means "equal night".

• Sunlight strikes the earth most directly at the equator.

• This occurs twice a year.

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

• Equinox literally means "equal night".

• Sunlight strikes the earth most directly at the equator.

• This occurs twice a year.

Equinox

• The vernal (spring) equinox occurs March 21.

• The autumnal (fall) equinox occurs September 21.

• The vernal (spring) equinox occurs March 21.

• The autumnal (fall) equinox occurs September 21.

Seasons Interactive

• Interactive• Interactive

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

distance from the Sun throughout the year.

The seasons are the result of the tilt of the Earth's axis.

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

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

http://www.nmm.ac.uk/uploads/gif/seasons-full.gif

Mechanism of the Seasons Video

Dramatization of Earth’s Seasons

• I need two volunteers.• One will hold the “Earth”.• One will hold the “Sun”.

• Earth should be tilted at what degrees?• The Earth should rotate around the sun in

what shape?

• I need two volunteers.• One will hold the “Earth”.• One will hold the “Sun”.

• Earth should be tilted at what degrees?• The Earth should rotate around the sun in

what shape?

Dramatization of Earth’s Seasons

• Tell the Earth to stop when it is at summer.• Tell the Earth to stop when it is at winter.

• At which point is the Earth having the longest day?

• At which point is the Earth having the shortest days?

• Tell the Earth to stop when it is at summer.• Tell the Earth to stop when it is at winter.

• At which point is the Earth having the longest day?

• At which point is the Earth having the shortest days?

Review Questions• What causes the seasons?

• At what angle is Earth tilted on its axis?

• Is the Northern Hemisphere pointed toward the sun or away from the sun during summer?

• Which season do we have the longest days?

• What causes the seasons?

• At what angle is Earth tilted on its axis?

• Is the Northern Hemisphere pointed toward the sun or away from the sun during summer?

• Which season do we have the longest days?