Investigation question: How and why does the appearance of the Moon change over time?
The appearance of the Moon is an astronomical phenomenon that many of us are familiar with from our daily life. However, very few people pay careful attention to how its appearance changes. You may have some familiarity with its changing appearance, and to begin this investigation, you should use your prior experience to help you make a prediction.
Using a set of Moon images provided by your instructor, put them in a sequence that you think represents an answer to the investigation question above; that is, arrange the images so that they show how you predict the Moon’s appearance changes over time.
Along with members of your group, come up with a plan to make observations of the Moon as seen locally to record in your science notebook. Your plan should provide you with enough observations that you think you will be able to adequately answer the question for how the Moon’s appearance changes over time. You should also decide how you will record the appearance of the Moon, and what other information about the observation you think is important to include in your science notebook. You should put your plan in to action, record 1 to 3 observations of the Moon, and share all of the data recorded by group members with everyone in the group.
After making your first 2 to 3 observations, you need to debrief those observations in your group and revise your data collection plan as necessary. Questions to ask yourself at this stage are:
- Are your plans for obtaining data looking good enough to gather at least 4 to 5 unique observations over the first two weeks of this investigation? Where and when are you trying to make observations?
- Has the weather been a challenge? If so, how might you obtain data on the Moon to use in this investigation if the weather does not clear up?
- Do you see any pattern in your observations so far? Does the pattern match with your predictions? You may want to add some thoughts comparing your observations so far to your prediction and if your thinking has changed at all since you recorded your prediction.
Starry Night and other planetarium software
At Penn State, we use the planetarium software package Starry Night Enthusiast 8 to simulate the appearance of the sky. Software of this sort is a very powerful tool for data gathering for an investigation like this one, as it allows you to change your viewing location, the day & time of your observation, and to include a wide variety of reference markers to images of the sky. Figure 1.1.1 above, shows a simulated image of the night sky from Penn State’s University Park campus on a night when the Moon was visible. This figure can be used as one piece of data for your investigation if you think it can be useful to your data collection. Starry Night Enthusiast is a commercial software package that students must purchase to use in this class. However, there are many other applications and websites that can be used to do similar simulations of the sky. One free option is the open source software application called Stellarium.
Students can use data from Starry Night or Stellarium to supplement their own observations of the Moon in this investigation. Some questions to consider before adding simulated data to your notebook are:
- Do you need to somehow verify that the images from planetarium software applications are correct? If so, how might you do this verification?
- Should data from a simulation be recorded in your science notebook any differently than your direct observations?
Analyzing your data and writing a claim supported by evidence
Once your group has collected a significant amount of data, you will need to analyze them in order to answer the investigation question. The first part of the question asks how the Moon’s appearance changes over time, and your group should have completed a prediction that can be revisited here as you consider your answer to the investigation question. Questions to consider at this stage of the investigation are:
- Do you see a pattern in your data for how the Moon’s appearance changes?
- Can you see the entire pattern or just part of it?
- If you believe you have identified the complete pattern, how do you know?
- How does the pattern in your data compare to that of your prediction?
After considering these questions, your group should write a concise statement that answer the how part of the investigation question, that is: “How does the Moon’s appearance change over time?”. Your claim should be as detailed as necessary to answer the question as completely as you can using the evidence you have, but it should also be relatively short, approximately 2 sentences or so.
Now, your group should reconsider your data and identify the data that provide the best evidence for the statement you wrote as your claim. That is, if you claim to see a pattern in the Moon’s behavior, which of your observations revealed that pattern?
Building a model to provide scientific reasoning to support your claim
The investigation question does not just ask how the Moon’s appearance changes with time, it also asks why the Moon behaves that way. From just your observations alone, it is unlikely that you can answer why the Moon behaves this way. It is at this stage of an investigation that scientists often construct a model that can help explain the phenomenon being studied. For the Moon, we recommend two different models that you can use to help explain your observations. The first is a “kinesthetic” model, where you can use your body and some simple tools to simulate the system that includes the Moon. The second is an interactive animation that provides different perspectives for investigating the behavior of the Moon.
Model 1: The kinesthetic Sun, Earth, Moon model
In your darkened classroom, you should have a lamp with no shade to simulate the Sun, and each student in the group should have a white, dylite-foam ball on a stick to simulate the Moon. Your instructor will walk you through how to use these items to simulate the Moon’s behavior. In our class, we ask students a series of questions to assist them in building understanding of the Moon’s behavior. These are:
- In this model, the lamp represents the Sun, and the foam ball represents the Moon. What represents the Earth?
- Can you use your foam ball and the lamp to simulate the appearance of a New Moon? How about a crescent Moon? Experiment with trying to simulate each of the observations you made of the Moon.
- In this model, how much of the Moon is being illuminated by the Sun at different times?
- What changes about the Moon that causes its appearance to change as seen from Earth?
- Identify the direction in which Earth’s shadow is pointing. Are there any times when the Moon is in Earth’s shadow?
Model 2: Interactive Moon animation from the University of Nebraska Astronomy Applet Project (NAAP)
After experimenting with the kinesthetic model for the Moon, you can use an interactive simulator to also study the Moon’s behavior: NAAP Lunar Phases Simulator
In this simulator, three views give you three different perspectives on the appearance of the Moon. The largest frame on the left shows you the Sun, the Earth, the Moon, and a stick figure on the Earth to represent your location. When you click on “Start Animation”, you will see the system begin to move. As the system moves, the view of the Moon for the stick figure is shown in the upper right panel. The lower right panel shows the relative location on the sky of the Sun and the Moon seen from the Earth-based perspective. In your groups, you should answer the following questions about the simulator:
- Can you create each phase of the Moon like you were able to in the kinesthetic model?
- Does the animation show the same behavior as the kinesthetic model? If yes, how? If not, why not?
- Can you explain each of your observations of the Moon by manipulating this model to reproduce your observations?
After completing these two modeling exercises, your group should be able to write an additional piece of your claim that answers “Why does the Moon’s appearance change over time?”. Come to agreement in your group for an explanation that explains the pattern you observed in your data.
Your investigation answering the investigation question posed above is now complete. However, you may still be wondering about some behavior of the Moon you witnessed when you were observing it by eye, observing it in Starry Night, or simulating its behavior with one of the two models used in this investigation. It is often the case that scientists still have wonderings about a phenomenon even after an investigation is complete, and those wonderings often form the basis for future research. If you have some now, you should record those in your notebook, too. You can certainly investigate those on your own, discuss them with your instructors, or read about them in an astronomy textbook.
Once an investigation is complete and a claim is presented that is supported by evidence and reasoning, scientists often present their work to others via presentations or in publications. The community of scientists spends significant time reviewing the work of others, trying to reproduce their results, and critiquing the work of others if they think the original authors may have missed something. Over time, the claims that continue to be supported with more and more evidence get widely accepted as the scientifically “correct” answers to how things behave. Assuming that your classmates and instructors agree with your claim, you can now take that claim as the scientifically accepted explanation for the Moon’s behavior.