Seasons: Earth, Moon, and Sun

Learning Target

• Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons.

Success Criteria

• Students understand the patterns that determine the causes of the seasons.
• Students understand the patterns that determine the causes of day and night.

Questions to Ponder

• Suppose you were stranded on a desert island without a calendar or clock. How would you know when a day, a month, or a year had passed?
• How could you tell what time of year it was?

Gizmo Warm-up

• Thousands of years ago, people told time by looking at the sky. You may not think about it, but you probably do this as well. For example, you know a day has passed when the Sun rises, it grows light outside, and then Sun sets again. In the Seasons: Earth, Moon, and Sun Gizmo, you will learn how you can relate the passage of time to different astronomical events.

Drag the Simulation speed slider all the way to the left.

Click Play and observe the SIMULATION pane.

• What happens?
• Click on the 2D VIEW tab. What do you see?
• Click on the DAY GRAPH tab. What do you see?
• Click on the SHADOWS tab. What do you see?

Activity A: Days, months, and years

Get the Gizmo ready:

• Click Reset
• Select the 2D VIEW tab.

Question: What astronomical events coincide with the passage of a day, month, or year?

1. Observe: Click Play. Observe how the position of the red dot in the SIMULATION pane relates to the cycle of night and day on the 2D VIEW tab. What astronomical event causes day and night?
   • Every time Earth finishes one rotation on its axis, a complete cycle of day and night occurs. In the SIMULATION pane, Earth’s axis is represented by the red line that goes through the center of the planet.
2. Describe: Months are another unit of time based on an astronomical event. Click Reset, and move the Simulation speed slider to the right a quarter of the way. Click Play, and observe the movements of Earth and the Moon for one month. (Note: You can use the calendar in the upper right corner of the 2D VIEW tab to determine when a month has passed.)
   • Describe the movements of Earth and the Moon over the course of a month.
   • What astronomical event corresponds to the passage of one month?
   • It takes approximately 28 days for the Moon to revolve around Earth. Revolution is the elliptical motion of a body traveling around another body in space.
3. Diagram: Click Reset. Set the Simulation speed to maximum. Click Play, and observe the movement of Earth over the course of one year. In the diagram below(Diagram A), draw how the position of Earth changes.
   • What astronomical event corresponds to the passage of 1 year?
   • How long does it take Earth to revolve around the Sun?

Activity B: Sun’s path

Get the Gizmo ready:

• Click Reset.
• Set the Simulation speed to minimum.

Question: What causes the Sun to appear to move in a path across the sky?

1. Observe: Select the 2D VIEW tab. Click Play, and watch the apparent motion of the Sun across the sky. In the diagram below (Diagram B), draw an arrow to show the Sun’s direction and path. Mark the highest altitude the Sun reaches with an X. Altitude is the distance an object appears to be above the horizon. The horizon is the line along which the sky and the Earth appear to meet.
2. Make a rule: On the 2D VIEW tab, E stands for east and W stands for west. Knowing this, you can conclude that the Sun rises in the __________ and sets in the __________.
3. Analyze: The Sun’s azimuth is the direction of the Sun in the sky. Azimuth is measured in degrees. Look at the diagram below (Diagram C.)
   • What is the Sun’s approximate azimuth when it rises?
   • What is the Sun’s approximate azimuth when it sets?
4. Summarize: Select the SHADOWS tab. Click Play, and observe the Azimuth. How does the Sun’s azimuth change over the course of the day?
5. Describe: Click Reset. Select the 2D VIEW tab. On the SIMULATION pane, the red dot on Earth represents where the observer who is seeing the scene on the 2D VIEW tab is standing. Describe the position of the red dot in the SIMULATION pane at midnight.
6. Observe: Click Play. When the Sun begins to rise on the 2D VIEW, click Pause. How has the position of the red dot changed?
7. Observe: Click Play again. When the Sun begins to set on the 2D VIEW, click Pause. How has the position of the red dot changed?
8. Draw conclusions: What causes the apparent motion of the Sun across the sky: the movement of Earth or the movement of the Sun? Explain.
9. Predict: A shadow is caused when an object blocks sunlight. For example, when your body blocks sunlight, you may see a shadow of yourself on the ground. How do you think the shadow of an object, such as a flagpole, would change over the course of the day as the Sun appears to move across the sky?
10. Observe: Click Reset. Select the SHADOWS tab, and click Play. Observe the Overhead and Projection view of the Shadow of a stick. What do you notice?
11. Compare: As you watch the shadow move, observe how its length changes in comparison to the Altitude of the Sun.
    • Describe the length of the shadow when the Sun is at its highest altitude.
    • Why does the Sun’s altitude affect shadow length?

Activity C: Sunrise and sunset times

Get the Gizmo ready:

• Click Reset.
• Select the DESCRIPTION tab.
• Set the Simulation speed to minimum.

Question: What factors affect sunrise and sunset times?

1. On your own: Latitude is a location’s distance north or south of the equator. You can use Google™ or another search engine to look up your town’s latitude. What is the latitude of your town? Use the Latitude slider on the DESCRIPTION tab to set the Gizmo to your town’s latitude.
2. Collect data: Select the GRAPH tab and check that Day graph is selected. Click Play, and observe. The solar intensity curve goes up at sunrise and goes down at sunset. Click Reset. Use the red date slider at lower right to set the date to March 21. Click Play, and then click Pause after the sun sets. Use the Day graph (found below - copy into your notebook) to record the approximate sunrise and sunset times in the table below. (Note: The Gizmo does not take Daylight Saving Time into account.)

Click Reset, and repeat the activity above for the other dates listed in the table. Then calculate the hours of daylight for each of the four dates.

1. Compare: How do sunrise times, sunset times, and hours of daylight change over the course of the year?
2. Analyze: Equinoxes are dates on which the daytime lasts as long as the nighttime. Solstices are the dates of the longest and shortest daytimes of the year.
   • Which two dates are equinoxes?
   • How does the amount of daylight during the summer solstice (June 21) compare to that on the winter solstice (December 21)?
3. Diagram: Click Reset. Move the date slider to each of the equinox and solstice dates. Examine how moving the date slider makes the position of Earth on the SIMULATION pane change. In the diagram below (Diagram D - copy into your notebook), mark Earth’s position and the position of Earth’s axis on each date. Shade in the part of Earth not lit by the Sun.
4. Compare: Use the SHADOWS tab to compare the Altitude of the Sun on the summer and winter solstices. Draw the highest altitude the Sun reaches on each of those two dates in the graphs below (copy into your notebook). On which date does the Sun reach the highest altitude?
5. Collect data: Use the observations you have made to answer the following question: What do you think causes the changes in sunrise and sunset times over the course of the year?
6. Hypothesize: How do you think latitude affects sunrise and sunset times?

Back to Teams...

1. Read Pages 76-77 in the PBIS Astronomy Text.
2. Answer the following questions:
   • What astronomical events coincide with the passage of a day, month, or year?
   • What causes the Sun to appear to move in a path across the sky?
   • What factors affect sunrise and sunset times?

The Big Ideas

• Although you cannot feel it, the planet you live on is hurtling through space at approximately 107,000 kilometers (66,000 miles) per hour.
• Earth’s movements are the basis of our units of time.
  • 24 hours equals one Earth day, or the time it takes Earth to rotate on its axis.
  • 365 days equals one Earth year, or the time it takes Earth to revolve around the Sun.
• Careful observation will show you that the Sun’s apparent path across the sky is not identical over the course of a year. In the northern hemisphere, the Sun’s azimuth seems to move southward in the winter and northward in the summer. The reason for this has to do with the tilt of Earth’s axis.
  • In the summer, the top of the axis is tilted towards the Sun. In the Northern Hemisphere, this causes longer daylight hours and the Sun to appear at a higher altitude in the sky.
  • In the winter, the top of the axis is tilted away from the Sun. In the Northern Hemisphere, this causes shorter daylight hours and the Sun to appear at a lower altitude in the sky. The shortest day of the year at northern latitudes is the winter solstice, which usually falls on December 21. That same date is the summer solstice at southern latitudes. Thus, December 21 is the longest day of the year south of the equator.