Overview & Purpose:

            This lesson addresses the common misconception for the cause of the seasons, namely that many students believe that Earth is colder in winter because it is farther away. They do not consider that the seasons are caused by Earth’s axis of rotation is tilted such that the North Pole points toward the Sun during Summer and away from the Sun in Winter, an effect that overwhelms the minor effect that Earth is actually closer to the Sun in Winter than it is during Summer.

Standards Addressed:

Standard 1- Scientific Inquiry:

Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing, creative process.

Key Idea 2: Beyond the use of reasoning and consensus, scientific inquiry involves the testing of proposed explanations involving the use of conventional techniques and procedures and usually requiring considerable ingenuity.

Key Idea 3: The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into phenomena.

Standard 6 - Interconnectedness: Common Themes - Models

Key Idea 2: Models are simplified representations of objects, structures, or systems used in analysis, explanation, interpretation, or design.

Standard 6- Patterns of Change:

Key Idea 5: Identifying patterns of change is necessary for making predictions about future behavior and conditions.

Standard 4 – Science:

P.I.1.1- Explain complex phenomena, such as tides, variations in day length, solar insolation, apparent motion of the planets, and annual traverse of the constellations.

1.1a-Most objects in the solar system are in regular and predictable motion.

These motions explain such phenomena as the day, the year, seasons, phases of the

Moon, eclipses, and tides.

1.1d- Earth rotates on an imaginary axis at a rate of 15 degrees per hour. To people on

Earth, this turning of the planet makes it seem as though the Sun, the moon, and the stars are moving around Earth once a day. Rotation provides a basis for our system of local time; meridians of longitude are the basis for time zones.

1.1f- Earth’s changing position with regard to the Sun and the moon has noticeable effects.

·  Earth revolves around the Sun with its rotational axis tilted at 23.5 degrees to a line perpendicular to the plane of its orbit, with the North Pole aligned with Polaris.

·  During Earth’s one-year period of revolution, the tilt of its axis results in changes in the angle of incidence of the Sun’s rays at a given latitude; these changes cause variation in the heating of the surface. This produces seasonal variation in weather.

1.1h- The Sun’s apparent path through the sky varies with latitude and season.

P.I. 2.1- Use the concepts of density and heat energy to explain observations of weather patterns, seasonal changes, and the movements of Earth’s plates.

2.1a- Earth systems have internal and external sources of energy, both of which create heat.

2.1i- Seasonal changes can be explained using concepts of density and heat energy.

These changes include the shifting of global temperature zones, the shifting of planetary wind and ocean current patterns, the occurrence of monsoons, hurricanes, flooding, and severe weather.

P.I. 2.2- Explain how incoming solar radiation, ocean currents, and landmasses affect weather and climate.

2.2a- Insolation (solar radiation) heats Earth’s surface and atmosphere unequally due to variations in:

·  The intensity caused by differences in atmospheric transparency and angle of incidence which vary with time of day, latitude, and season

·  Characteristics of the materials absorbing the energy such as color, texture, transparency, state of matter, and specific heat

·  Duration, which varies with seasons and latitude.

Objectives:

Students will be able to understand, explain, and translate concepts to hypothetical situations involving:

• Cause of seasonal change
• Importance of angle of insolation and axial inclination
• Insignificance of orbital distance in affecting the seasons
• Extensions may include an understanding of the length of daylight and how it varies seasonally

Materials Needed:

Insolation model kit: 1-Globe (or a ball with latitude and longitude lines), meter stick, 1 lamp with stand, Velcro with adhesive backing, 0.45 mA solar panel, milliammeter (0 to 50 mAmp range), 1/8” plexiglass spacer, folded cardboard wedge (acts like a brake to keep the globe from rotating), electrical wires, and graph paper. 

Demonstration Materials: globe and flashlight

Preparation:

(0.5 to 1 hours to setup) Note it may take longer to locate items depending on item availability. After initial assembly of apparatus, set-up time should be minimal. Gather items and place each set of equipment into boxes so students can setup quickly.

In the Lab:

To simplify the task to save time make a template out of cardboard with the distances for winter solstice, equinox and summer solstice.  Mark the desks with chalk, washable marker or masking tape with the distances.  (10- 15 minutes) 

Lesson Outline (7E model of Eisencraft, 2003)

Elicit:

            Students’ prior knowledge will be elicited questioning them as to what they think causes Earth’s seasons. Students will phrase their understanding in the form of an hypothesis (Question 1 on lab handout) and through their predictions recorded in Procedure 1 on the Handout. It is expected that greater than half of any student group will believe that Earth’s Season’s are caused by changing distance between the Earth and Sun.

Engage:

            Teachers may engage students by generating enthusiasm through prodding the students’ regarding their beliefs. Students that believe the seasons are caused by distance changes may be challenged to defend their positions and students that already have some understanding of the correct cause of the seasons may be asked to “prove the teacher wrong.”

Explore:

            Students will explore the true cause of Earth’s seasons via guided inquiry as outlined in the lab handout (Procedures 1-4.

Explain:

            Because students with misconceptions confront those misconceptions through steps of the lab, very little explanation by the teacher should be required. However, some students may cling to their misconceptions despite the contradictory data generated in the lab. These students may require individualized explanation by the instructor.

Elaborate and Evaluate:

            Students will elaborate upon their newly acquired understanding through the targeted questions (2-5) on the lab handout. These questions also require students to evaluate their understanding. Teachers may evaluate the extent of students’ conceptual change through their answers to questions 2-5 and through informal discussions with students.

Extend:

            Students can extend their understanding through the extension questions (6-7) on their lab handout. Through these questions, students are asked to recognize the equinoxes based on their results from the two solstice positions. This may lead to further testing using the model by which students position the globe to correspond to an equinox orientation and measure incident light using the solar cell and milliammeter. They may then compare their data to that which they measured for the solstice positions. They will also reinforce their understanding of the importance of axial inclination by predicting the effect of a bolide impact which changes axial tilt (question 7). If time permits, students may also use the insolation model to test their predictions of the effects of increased tilt.

Safety Considerations:

Caution needs to be taken with the 200-watt bulb and flood light bulbs because they get very HOT if left on.  Cords of lamps may pose a tripping hazard. Lamps should also be kept away from water supplies in the lab

1.