NAMES: ___________________________
DATE: ________________ ___________________________
PERIOD: __________
In a famous short film, entitled "A Private Universe," interviewers attend graduation at Harvard University and ask graduates and faculty members to explain what causes the changes of the seasons. The explanations, even at Harvard, reveal the remarkable depth of misunderstanding that surrounds this concept.
Many people interviewed believed that Earth is closer to the Sun during summer and farther away during winter. This belief is common, but it is not true. (Also, if this were what caused the seasons, the whole Earth would have summer at the same time and winter at the same time. This is not the case either - summertime in the northern hemisphere is wintertime in the southern hemisphere, and vice versa.)
In this module, you will see that the seasons are actually caused by the angle or directness of the Sun's rays.
Temperature and the Angle of the Suns Rays
In this activity, you will explore how the angle of a fixed-size plate affects the number of rays that strike it.
1. In the Gizmotm, click the PLATE tab. In the DESCRIPTION pane, be sure that Time A is selected. Then click on the TABLE tab. This is where the data from this experiment will be recorded.
1. Use the slider to set the Axis angle of the plate to 0�. (To set a slider to a specific number, type the number in the field to the right of the slider and click ENTER.) The plate is now directly facing the sun. Click Fire and watch the rays from the Sun strike the plate.
How many rays strike the plate when it is set at an angle of 0? __________
2. Click Reset ( ), change the angle to 20�, and click Fire.
How many rays strike the plate in this case? __________
3. With the TABLE tab still selected, click Reset and repeat the process for angles of 40�, 60�, and 80�. REMEMBER TO HIT ENTER EVERY TIME YOU CHANGE THE VALUE OF THE ANGLE!!!
How many rays strike the plate in each case?
40� __________
60� __________
80�. __________
4. Experiment with an Axis angle of 30� and ?30�.
How does the plate look different at an angle of 30 compared with an angle of ?30�? ________________________________________
How many rays strike the plate for each angle?
30� __________
?30� __________
2. Make sure that Time A is still selected in the DESCRIPTION pane. Click the EARTH tab. Earth is displayed with its surface broken up into a number of plates.
1. For what plates is it daytime? __________
For what plates is it nighttime? __________
How can you tell? (Hint: Notice where the Sun is located.)
________________________________________
2. Click the TABLE tab. With the Axis angle set to 0�, click Fire. Why did plates H, I, J, K, and L not experience any hits from the Sun's rays?
________________________________________
3. You should have seen that plates B, C, D, E, and F were hit by some of the Sun's rays.
Of these plates, which one was hit by the most rays? __________
Of these plates, which ones experienced the fewest hits? Explain why.
__________________________________________________
4. Average temperatures in a region are related to the number of hits experienced by that region.
Of plates B, C, D, E, and F, which one lies in a region that would be experiencing the warmest temperatures? __________
5. Select Show axis. The Earth rotates once a day around the axis shown in the Gizmo.
Twelve hours after the moment shown, how many hits from the Sun's rays would plates B, C, D, E, and F receive? __________
How many hits from the Sun's rays would plates H, I, J, K, and L receive?
H __________
I __________
J __________
K __________
L __________
Explain. __________________________________________________
Causes of the Seasons
In this activity, you will see that the cause of the seasons is the tilt of Earth's axis.
1. Click Reset and make sure that Time A is selected in the DESCRIPTION pane. Click EARTH to display the EARTH pane. Select Show axis to display Earth's axis. Set Angle to 23� to represent the actual tilt of Earth on its axis. (You can also click the Earth axis angle button to do the same thing.) Assume north is at plate A, at the top of the axis.
1. Which plate is at the location of the South Pole? __________
Which plates lie on the equator? (The equator circles the middle of the earth, and runs perpendicular to the Earth's axis of rotation. Keep in mind that, because the axis is angled, so is the equator.) ____________________
2. Display the TABLE pane and click Fire. Which plate experiences the greatest number of hits? (Click on the BAR CHART and GRAPH tabs to see the same information displayed in different ways.) ____________________
3. Because plate D is on the equator, plates C and E represent similar latitudes. The center of plate C is about 30� north of the equator and the center of plate E is at about 30� south of the equator. On average, over a full year, plates C and E experience similar climates.
As it is currently shown in the Gizmo, which plate is experiencing more hits from the rays of the Sun, plate C or E? __________
Which of those two plates is experiencing warmer-than-average conditions? __________
Which is experiencing colder-than-average conditions? __________
4. Based on your previous answer, what season is plate E experiencing?
____________________
What season is plate C experiencing? ____________________
5. Would you say that the Earth is positioned like this in June or in December? Explain.
____________________________________________________________
6. Is it summer or winter where plate K is located? __________
How about where plate I is located? Explain. (Hint: Think of how the Earth would look in twelve hours, after it rotates a half-turn.)
____________________________________________________________
7. You should have found that it is summer where plate E is located. Explain why this means that it is summer in the entire southern hemisphere.
____________________________________________________________
2. With the EARTH pane still visible, click Reset. Be sure that Show axis is selected, and the Axis angle is set to 23�. Click the DESCRIPTION tab. Under Gizmo Status, two options are shown. Time A means now, and Time A + 6 months means six months from now.
1. Select Time A in the DESCRIPTION pane. Look at the configuration of Earth with respect to the Sun. Now select Time A + 6 months in the DESCRIPTION pane.
How is the Earth positioned when compared to how it was six months before? __________________________________________________
Was there any change in the tilt of Earth on its axis? __________
Explain. __________________________________________________
2. With Time A + 6 months selected, display the TABLE pane (or BAR CHART pane or GRAPH pane). Click Fire.
Which plate experiences the greatest number of hits? __________
Is this plate in the northern or the southern hemisphere? __________
How many hits does the corresponding plate in the opposite hemisphere experience? __________
3. What season is the northern hemisphere experiencing with Earth in this position? ____________________
What season is the southern hemisphere experiencing? __________
4. In six more months, how would the previous answers change?
____________________________________________________________
5. The Gizmo does not give you a Time A + 12 months option. Explain why this is not necessary.
____________________________________________________________