Day 11

Sun – Earth SystemInvestigation 3 part 2

Review

• Review the following questions from “Wendy and Her Worldwide Weather Watchers”:

• When one location on Earth has 14 hours of daylight, is all the rest of the world having 14 hours of daylight as well?

• Is the longest day of the year the same length all over the world?

Review

• Is the shortest day of the year the same day all over the world?

• Are the longest days always in the summer?• Are the shortest days always in the winter?

• What ideas do you have to explain why daylight hours change over a year?

Sun-Earth Model

• Represent the Earth and the Sun

• How should I set up the model?

Sun-Earth Model

RevolutionThe movement of one object around another

The Earth revolves around the Sun

Takes 365 days or 1 year

Rotation

Earth has a North and South Pole

Axis is the imaginary line that if you connect the North and South Pole

The Earth turning on its axis

The axis is tipped over at an angle of 23.5˚

One turn on it axis takes 1 day or 24 hours

Rotation

• How do we know where it is day and where it is night on this globe?

Day

Night

How much of the globe is in daylight at any given time?

Always exactly half illuminated and half dark

North Star (called Polaris)

Always positioned directly over Earth’s North Pole

Used as a navigation aid to seafarers and explorers for centuries

Summary

• Is there a part of Earth that experiences only daylight or only darkness during the year?

Above the Arctic Circle

Below the Antarctic Circle

Equinox Two days during the year that day and night hours are equal

Comes from Latin meaning “equal night”

Vernal equinoxoccurs around March 21

Spring Equinox

Fall EquinoxAutumnal equinoxoccurs around September 21

Longest Day in the Northern Hemisphere?

• Which way is the North Pole tilted?– Toward the Sun

Solstices

Around June 21

The longest day of the year

Solstice means “sun stands still”

Summer Solstice

Around December 21

The shortest day of the year

Winter Solstice

• At fall equinox– North Pole is tilted

neither toward nor away from the Sun

– Sun is directly over the equator

– Half in daylight and half in darkness

• At summer solstice– North Pole is tilted

toward the Sun– Northern Hemisphere

receives more sunlight

• At summer solstice– North Pole is tilted

toward the Sun– Northern Hemisphere

receives more sunlight

• At summer solstice– North Pole is tilted

toward the Sun– Northern Hemisphere

receives more sunlight

• At winter solstice– North Pole is now

tilted away from the Sun

– Shortest day of the year

• At spring equinox– Sun is directly over the

equator– Day and night are

equal

• At spring equinox– Days are getting

longer– Exposure to light

is increasing, raising temperatures

• At fall equinox– Days are getting

shorter– Less exposure to

light, lower temperatures

• At winter solstice– Days are shortest– Less exposure to

light, lower temperatures

– Snow, ice, frost, etc

• At summer solstice– Days are longer– Longer exposure to

light produces the effects of summer

– Warmer temperatures, plant growth

Reading

• Read “Seasons” starting on page 17 of your green resource book.