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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.