Reasons for the Seasons (Lab Activity)

We started our Astronomy unit last week.  In middle school, astronomy consists learning about the movements of the Earth, Moon and Sun.  Our Ohio Science Standard states "The relative patterns of motion and positions of the Earth, Moon and Sun cause solar and lunar eclipses, tides and phases of the moon."  I really enjoy teaching this unit because there are many hands on demonstrations that we can do in class, and students can make observations on their own (they love doing this) that we can discuss in class.  

We began last week discussing the difference between Earth's Rotation (day vs night) and Earth's Orbit (revolution) around the sun.  By Wednesday, we were talking about Earth's orbit, the tilt of Earth's axis and the seasons.  On Thursday, students completed the lab, Reasons for the Seasons, in which they investigated the question:  How does the tilt of Earth's axis affect the light received by Earth as it revolves around the sun?

They used light bulbs (borrowed from the fifth grade teachers electricity unit supplies), foam balls that I found in our craft closet, toothpicks (I brought from home), protractors (borrowed from our math teacher), rulers, and pencils.

 Side note:   I really love completing lab investigations when I can find all of the supplies I need without spending any money.  

Students drew dots at the top and bottom of the foam balls to represent the poles and line around the center to represent the equator.  Next, they used a pencil to represent the axis and stuck it into the south pole of their foam balls.  They used stacks of books to find the right height for their light bulb sun and then used the protractor to measure a 23.5 degree angle, tilting their foam Earth away from the sun representing winter in the northern hemisphere.  

Next, students stuck a toothpick straight into the model Earth about halfway between the equator and the North Pole.  They observed and recorded the length of the toothpick's shadow in millimeters.  

Students then rotated their model Earth without changing the tilt (this was difficult for them) and recorded how the shadow changed.  After rotating the model Earth back to its original position, students tilted the model 23.5 degrees toward the sun representing summer in the northern hemisphere and recorded the length of the toothpick's shadow.  

While doing this, I asked students to pay close attention to the pattern of light hitting the model Earth.  

They discussed these questions:

1. When it is winter in the Northern Hemisphere, which areas on Earth get the most concentrated light?  Which areas get the most concentrated light when it is summer in the Northern Hemisphere?
2. Compare your observations of how the light hits the area halfway between the equator and the North Pole during winter and during summer.
3. According to your observations, which areas on Earth are consistently coolest?  Which areas are consistently warmest? why?
4. What time of hear will the toothpick's shadow be longest?  When will the shadow be shortest?
5. How are the amounts of heat and light received on Earth related to the angle of the Sun's rays?
6. Use your observations of an Earth-sun model to write an explanation of what causes the seasons.

This activity took an entire (42 minute) class period, but we discussed and shared answers to the questions the following day which was a great transition in to a discussion on the seasons, equinoxes and solstices.  In fact, at the conclusion of our discussion, I had all groups share their answers to question 6, which lead to our next discussion.