LEARNING GOALSLEARNING GOALS

• I will be able to graph and analyze sunlight data.

• I will discuss seasonal variation in day length as a consequence of axis tilt, rotation, and revolution.

GRAPH QUESTIONSGRAPH QUESTIONS• What does the graph reveal about the

amount of daylight over a year in Berkley?– Days get longer from January to June,

shorter from June to December• When do people in Berkley have their

longest day? Shortest?– Longest= June, Shortest= December

• When do people in Berkley have about 12 hours of daylight?– March and September

GRAPH QUESTIONSGRAPH QUESTIONS• How many hours of daylight do

people in Berkley have on their longest day? On their shortest day?–Longest= 14+, Shortest= 9+

• In what season do people in Berkley have their longest day? Their shortest day?–Longest= Summer, Shortest= Winter

GLOBAL DAYLIGHTGLOBAL DAYLIGHT• 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?

• Is the longest 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?

READING:READING:“Wendy and Her “Wendy and Her

Worldwide Weather Worldwide Weather Watchers”Watchers”

page 12page 12

Wendy and Her Worldwide Weather Watchers

****ANSWER ALL QUESTI ONS I N COMPLETE SENTENCES. USE THE QUESTI ON TO ANSWER THE QUESTI ON. 1. Which locations have the greatest number of hours of daylight on J une 21? The f ewest hours of daylight? Greatest=______________________________________________________________________________________________________________________________________________________________________________________________________________Fewest=____________________________________________________________________________________________________________________________________________________________________________________________ ___________________ 2. Which locations have the longest hours of daylight on December 21? The shortest hours of daylight? Longest=_______________________________________________________________________________________________________________________________________________________________________________________________________________Shortest=___________________________________________________________________________________________________________________________________________________________________________________________ ___________________ 3. Alpena, Michigan, is located 45 degrees north of the equator. How much daylight do you estimate they have on J une 21? On December 21? J une 21=_________________________________________________________________ December 21=_____________________________________________________________ 4. Boulder, Colorado, has a latitude of 40 degrees North. Wellington, New Zealand, has a latitude of 41 degrees South. Which city has the longest amount of daylight on J une 21? How do you know? _____________________________________________________________________________________________________________________________________________________________________________________________________________________

Seasons and Seasons and SunSun

GLOBAL DAYLIGHTGLOBAL DAYLIGHT• 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?

• Is the longest 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 What ideas do you have to explain why daylight to explain why daylight

hours change over a hours change over a year?year?

SUN-EARTH MODELSUN-EARTH MODEL• How should I set up the model?• Where should the Sun be and where

should Earth be?

REVOLVEREVOLVE• The movement of one object

around another.

• Earth revolves around the sun.

• How long does it take for Earth to make one revolution around the Sun?

–1 year or 365 days

AXISAXIS• Earth has a North Pole and a South Pole. These are the north and south ends of an imaginary axle, called an axis, on which Earth rotates.

ROTATIONROTATION• Earth turns like a top,

and this turning motion is called rotation.

• Earth does not spin straight up and down, but is tipped over at a significant angle of 23.5 degrees.

LET’S THINK…LET’S THINK…• How long does it take for Earth to

rotate (turn around once) on its axis?–1 day, or 24 hours

• How do we know where it is day and where it is night on these globes?–The side illuminated by the Sun is day,

the dark side is night.• How much of the globe is in daylight

at any given time?–The globe is always exactly half light,

and half dark. ALWAYS!

NORTH STARNORTH STAR• There is a star in the

night sky called Polaris, or the North Star. It is positioned directly over Earth’s North Pole. Earth’s North Pole always points to the North Star- summer, fall, winter, spring, day, and night.

NORTH STARNORTH STAR• That’s why the North Star has been a navigation aid to seafarers and explorers for centuries.

NORTH STARNORTH STAR• In our Sun-Earth system,

we need a North Star. You will have to visualize the North Star through this wall and way, way off in the distance. The North Pole of our model Earth will always point at the North Star as it revolves around our model Sun.

KEY QUESTIONKEY QUESTION• Why do hours of daylight differ depending on time of year and location on Earth?

• Use our model to help us figure it out.

KEY QUESTIONKEY QUESTION• Position Earth and the Sun on

the same plane.• Keep Earth’s North Pole pointed

at the North Star at all times.• Place Earth at various positions

around the Sun.• Rotate Earth on its axis at each

position, and observe the time in the light and the time out of the light.

DEMONSTRATION!DEMONSTRATION!For each stop, think about For each stop, think about

these questions.these questions.• Which region of Earth is getting the

greatest number of hours of daylight now?

• Which is experiencing the most hours of darkness?

• When Earth is at this point in its revolution, what season is it in the Northern Hemisphere (our town)?

SUMMARYSUMMARY• Is there a part of Earth that

experiences only daylight or only darkness?–Yes, above the Arctic Circle and

below the Antarctic Circle• Is there ever a time when the day and

night are equal everywhere on Earth?–Yes

• How many times does this happen during a revolution?–Twice!

EQUINOXEQUINOX• There are 2 days during the year that

day and night hours are equal. These days are called equinoxes. Equinox comes from Latin, meaning “equal night”. One equinox, the spring or vernal equinox, occurs around March 21.

• When do you think the other equinox occurs?–Around September 21, in the fall. This

equinox is the fall or autumnal equinox.

SOLSTICESOLSTICE• When is the longest

day of the year in the Northern Hemisphere?

• Which way is the North Pole tilted, toward the Sun or away from the Sun?

SOLSTICESOLSTICE• The longest day of the

year is the summer solstice. Solstice means “Sun stands still”.

• When is the shortest day of the year in the Northern Hemisphere?

• The shortest day of the year is the winter solstice.

SUN-EARTH SYSTEMSUN-EARTH SYSTEM

• Turn to this page in your lab books.

READING:READING:“Seasons”“Seasons”

page 17page 17

WORD BANK• Rotation- Earth turning around

on its axis. One rotation=24 hours.

• Revolution- One object moving around another. One Earth revolution around the Sun=365 ¼ days.

• Axis- Imaginary line from North to South pole on which Earth rotates. Tilted at 23.5 degrees.

WORD BANK• Polaris (North Star)- Star directly

over Earth’s North Pole. Always points North.

• Equinox- Day and night hours are equal.–Spring Equinox=March 21–Fall Equinox=September 21

• Summer Solstice- Longest day of the year. June 21

• Winter Solstice- Shortest day of the year. December 21

Seasons Simulation

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