Patterns and Predictability--Seasons

Earth Science Extras

by Russ Colson

We are going to examine a model (a mental picture or explanation of how some part of the universe works) for what causes seasons on Earth. However, simply 'learning' a model, or even being able to explain the model and apply the model to making predictions or solving problems, does not meet the Next Generation Science Standards goal for learning science as a practice rather than as a body of knowledge. Consequently, in an effort to begin where real science begins, we are first going to consider the observational evidence on which the model for seasons is based. In fact, this is how the oldest science, astronomy, began--with people noticing things, inferring patterns, and trying to figure out what those patterns tell us and what they predict.

Take 10 minutes or so to write down all the patterns that you have seen or know about that are observed in the heavens (try to limit yourself to observations in the sky that might reasonably bear on the cause of seasons). Don't be satisified with stopping after your first 2 or 3 observations, but rather think deeper--there are many observations that anyone can make that underpin our model for the cause of seasons. Then take another 10 minutes to search online to help prompt your memory or understanding of patterns in the heavens

Note: The Next Generation Science Standards (NGSS) was publshed by National Academies Press in 2013 and, as of this writing, is being adopted widely throughout the United States.

Be sure to read and jot down the observations that bear on Earth's seasons listed in the feedback to the question above, because we will refer to them in the following thought problems.

In particular, hang on to the observations related to how the sun moves across the sky (rising in the east and setting in the west; rising higher in the sky in summer than winter), and how the stars move (seeming to rotate around the north star; constellations changing with the seasons). If you don't understand what these observations refer to, do some work online to figure them out.

Here is another observation that is a bit harder to make without some geometry calculations and special tools for measuring: The sun is closer to the Earth in January than in July.

Which of the following models for what causes the seasons on Earth can be excluded based on the observation that the sun is closer to Earth in January than in July?

Any realistic model for seasons on Earth must address and explain ALL the observations that we make related to seasons.

So, let's consider a model for seasons on Earth that addresses all of these observations

Before watching the leccture below, spend some time looking around online to get a better understanding of the accepted model for what causes seasons. There are good illustrations and animations online. As you read about the model, and watch an animation, think about how the model can be figured out from the observational evidence. Searching on "season model" should get you a lot of good pictures.

As of this writing, here is a place to look at an interactive model for seasons:

https://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html

This model allows you to move the Earth around the sun and watch how the angle of sunlight changes with season.

Be sure to take notes as you watch the lecture below. (note: at 12:27 minutes, I point to the north pole to indicate 24 hours of daylight there in the summer, but inadvertently say 'equator' instead of north pole - hopefully not too confusing!)

Now, let's apply our model to a series of thought puzzles and challenges, trying to identify 1) what is wrong with a particular model and 2) what observations allow us to prove that a model is wrong.

In the following puzzles, the larger styrofoam ball represents the sun, and smaller ones represent the Earth in various seasons (as labeled), and the lollypop sticks represent the Earth's axis of rotation.

Ancient Astrology--science or mysticism?

Causation and correlation are two important ideas in science that mean different things. Correlation means that two things consistently happen together. Causation means that one thing causes the other to happen.

Astrology was the idea that the stars somehow exert magical powers over our lives here on earth, assigning a causal relationship between positions of the stars and events on Earth. In many cases, we no longer believe that the position of the stars has a direct causative influence over most events on Earth. However, to ancient people, it was very clear that the position of the sun in the sky and the movement of stars were correlated with events on Earth, a belief which continues in science today.

Because ancient people recognized the regular pattern of movements of heavenly bodies in the sky and the correlation of those movements with events on Earth, they became fascinated with (for example) the position of the sun at key times of the year, such as the equinox. This fascination is seen in the way that people groups all over the world built tombs oriented in accordance with important celestial directions. This fascination was more than merely mysticism.   Observing the heavens allowed people to predict the coming of key events important for living life.

Make a list of some correlations between the positions of the sun or stars and events on Earth. After thinking about this and writing down some of your ideas, do some searching online to see what other correlations you can find. Ask yourself, how did ancient people use the changing positions of the sun and stars for practical purposes in their lives?

Many people of the past have understood the connection between the changes in the stars and the changing of seasons. For example, Native Americans of Minnesota have a rich tradition of understanding the changes in the sky. As of this writing, you can find links to some ideas of Native American awareness of the association between star position and season at

https://www.nativeskywatchers.com/

A reminder: Science is based on observation, not theory

I have placed significant emphasis on observation in this lesson (rather than simply 'knowing and explaining' the model). An emphasis on observation is the foundational idea of science. In other words, theory is based on observation; observation is not based (intrinsically) on theory. Given that observations in the natural world underpin all science, consider and discuss with someone the following question.

"Does the universe have to obey the laws of nature or do the laws of nature have to obey the universe?"

Although a question of this sort can seem very abstract and irrelevant to life, it actually is quite significant in understanding what science is and how it plays out in our lives. When people make statements such as "it's just a theory" or they dismiss a scientific conclusion because they think "their theory" is just as good, it is often because they don't understand the fundamental nature of scientific investigation. Abstract ideas such as that implied in the question above also are important in considering how cultural differences play out in scientific investigation--many explanations and ways of explaining are possible, but what actually happens in the universe (that can potentially be observed) is independent of cultural expectation or explanation and therefore provides a place of common ground. That does not mean, of course, that our cultural biases or intuitive expectations don't influence which things we observe or how we interpret those observations.

last updated 3/27/2020.   Text and pictures are the property of Russ Colson.