Solstices and Equinoxes: Constructing Explanations by Developing and Using Models

scienceteachermamaAnalyzing and Interpreting Data, Asking Questions and Defining Problems, Cause and Effect, Constructing Explanations and Designing Solutions, Crosscutting Concepts, Developing and Using Models, Disciplinary Core Ideas (DCI), Earth and Space Science, Engaging in Argument from Evidence, Expressions and Equations, Measurement and Data, MS-ESS1: Earth's Place in the Universe, Patterns, Planning and Carrying Out Investigations, Science and Engineering Practices, Seasonal Change Unit, Stability and Change, Systems and System Models, Using Mathematics and Computational ThinkingLeave a Comment

Image by Przemyslaw "Blueshade" Idzkiewicz

Image by Przemyslaw “Blueshade” Idzkiewicz

By this point in the unit, students should have a clear understanding about what DOESN’T cause the seasons. Hopefully, misconceptions have been destroyed by the evidence we collected in class. Now it’s time to gather evidence that supports what DOES cause the seasons. We start with graphing the day length (photoperiod) of Northern Hemisphere locations, Southern Hemisphere locations, and Equatorial locations throughout the year and look for patterns. I show students video clips of a midnight sun. This phenomenon is intriguing for students and they are eager to figure out where and why this event happens. I can also link it to the next set of lessons on patterns of change in light intensity.

These lessons directly support the Mystery Class investigations which I highly recommend integrating your seasons unit with this program (January-May). Click here to see how I integrate Mystery Class into the seasonal change unit.  After these lessons, you can see the light bulb go off in students heads about how they can use this information to determine the latitude of their mystery class.

Download the free lesson plan using the NGSS 5E model templateSolstices and Equinoxes_Constructing Explanations by Developing and Using Models lesson plan. The lesson plans include directions and student work activities.

Brief Descriptions of Lessons:

Lesson 1: Graphing World-Wide Day-Length Changes and Analyzing Patterns of Seasonal Change

Students graph the daylight (photoperiod) data of several latitudes  (2 Northern Hemisphere, 2 Southern Hemisphere, and 1 Equatorial). They will compare their data to even more data provided by 2 web sources to analyze and interpret patterns in world-wide day length changes throughout the year. While analyzing the graphs students summarize what the graphs tell us about solstices, equinoxes, midnight sun, spring, summer, fall, winter, and the pattern of day-length changes throughout one year. I use the phenomenon of the midnight sun to motivate students to discover its cause by having developing and using models that match the data.

Lesson 2:   Developing and Using Models to Construct Explanations for the Patterns of World Wide  Day Length Changes

Students will use their models to test their ideas about what causes the seasonal changes in day length patterns and the midnight sun phenomenon. Once an explanation is discovered, they will sketch what the earth looks like for each solstice and equinox and then sketch a 2 dimensional model of one full revolution. They will complete a group quiz with questions deliberately created to pull out further misconceptions students may have. Finally, they will create a claims/evidence/reasoning chart to start recording the reasons for the seasons. Once the students have a model that explains why arctic and antarctic regions experience the midnight sun phenomenon, I challenge them with this question: If the North and South Pole receive 24 hours of daylight for 6 months out of the year, then why are they the hottest places in the world? This leads us to the next lessons. 

Specific Learning Outcomes:

  • Use graphical displays of large data sets to identify temporal and spatial relationships specifically that
  1. For any given latitude, spring and summer days have more hours of daylight and fall and winter nights are longer.
  2. In the Northern and Southern Hemispheres, day­ length changes (and seasons) are opposite one another during the year.
  3. Day length changes are more dramatic the farther away from the Equator.
  • Construct models to predict, explain, and/or collect data to test ideas about how Earth’s tilt affects day length hours.  Specifically:
  1. As the earth moves around the sun over the course of a year, the orientation of earth’s axis with respect to the  sun changes. This shift causes the length of daytime and nighttime at a place to  change and the amount of energy the place receives from the sun to change over the course of a year.
  • Apply scientific reasoning to summarize why the data are adequate for partially explaining seasonal changes.


Midnight Sun time-lapse videos:

Graphs to analyze world wide Day length changes :

Websites that explore equinox and solstice cultural traditions:


Article exploring the connection of day length and spring bloom: Backyard Science: How Do They Know It’s Spring

What the Earth looks like from space on the equinox:

Interesting article about equinox facts from National Geographic

Directions for making Earth models and light bulb sun models

Excellent formative assessment resources: 

“The items and other resources available on this site were developed by AAAS Project 2061 with funding from the National Science Foundation. The items are different from most multiple choice science test items in that they:

  1. assess students’ conceptual understanding, not just facts and definitions,
  2. test for common misconceptions and alternative ideas students have along with their correct ideas
  3. are precisely aligned to the science ideas they are intended to test”
  • This resource provides excellent formative assessments to engage students in argument from evidence. (Any Amazon links are affiliate links. This means I get a small percentage (4%) if you purchase this product. I only promote products that I have bought myself and found helpful. The proceeds are used to keep the blog running. Thank you!)

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