Earth Moon Sun Cover Photo
  • What’s in This Unit?

    Most students and many adults have no idea why the Moon looks different from night to night. For many, the predictable pattern of moon phases is just a mysterious and beautiful part of our night sky. In fact, understanding why we see the Moon as we do requires some fairly challenging spatial reasoning. This unit helps students gain a deeper understanding of everyday observations of the Moon, transforming the experience of Moon gazing into an act of profound and expansive perception.

    The Earth, Moon, and Sun unit begins as students take on the role of student astronomers, tasked with advising an astrophotographer who needs to take photographs of the Moon for a fictional magazine called About Space. The astrophotographer can only take pictures of specific features on the Moon at certain times, and this serves as the anchor phenomenon for the unit. In order to provide advice about when to take photographs of the Moon as well as how to take photographs of a lunar eclipse, students will need to investigate where the Moon’s light comes from, what causes the characteristic changes in the appearance of the Moon that we observe, and what conditions are required to view phenomena, such as particular moon phases and lunar eclipses. As students conduct these investigations, they will use a hands-on Moon Sphere Model, the digital Earth, Moon, and Sun Simulation, and the Earth, Moon, and Sun Modeling Tool to gather and represent information about the movement of and light patterns on the Moon. The Sim allows students to explore and manipulate the movement and relative positions of Earth and the Moon, observing these changing arrangements in space from various solar-system perspectives that are otherwise very difficult to imagine. The Modeling Tool allows students to explain what they find in the Sim. Through developing hypotheses and engaging in argumentation, students will come to an understanding about the phases of the Moon and its orbital positions, which they will then apply to their advice to the astrophotographer. By the end of the unit, students will be able to explain the mechanisms behind patterns of light and dark on the Moon, moon phases, and lunar eclipses.


    Studying planetary science in the context of the Earth, Moon, and sun system gives students an accessible and familiar starting point from which they can begin to understand the principles of illumination and orbit. These ideas are applicable to a broader understanding of star systems and planetary movement. Our ever-changing view of the Moon from Earth, which we characterize by naming phases of the Moon, is a phenomenon we all observe almost daily, but few of us ever examine it in any detail. Helping students to understand and predict the movement of Earth and the Moon and how this movement affects what we observe from Earth gives them a deeper experience as a resident on Earth and helps them to see how science is applicable to their daily lives.

    The challenge to help an astrophotographer predict when certain lunar events will take place invites students to consider questions that scientists first studied many centuries ago. This context adds motivation and interest to the unit. Moreover, it provides motivation for students to understand the light patterns on the Moon, which necessitates a thorough understanding of the movement of the Moon around Earth and the relative positions of the Moon, Earth, and the sun.

    Envisioning these three-dimensional relationships between planetary bodies is a challenging aspect of planetary science. The Earth, Moon and Sun unit, with its in-depth focus on relative positions of Earth and the Moon in space and how their alignment affects what we observe and experience, is a perfect opportunity for students to develop and deepen their spatial reasoning. This ability can sometimes be overlooked in academic settings but will serve students well in life.

    Another aspect of planetary science that can be challenging is the sheer vastness of space. Students will grapple with large numbers throughout their education: the number of cells in a body, the millions or billions of years in the history of life, of Earth, and of the solar system; the incomprehensibly large and small size of things from subatomic particles to star systems and galaxies. The Earth, Moon and Sun unit prompts students to consider some of these issues of scale by highlighting how models of the solar system must take into consideration the enormous size of planetary bodies and the distances between them. This also provides an opportunity for students to experience the value of models in science by demonstrating the utility of “not to scale” models in understanding a system we can’t take apart or manipulate ourselves.


    In their role as student astronomers, students begin by helping the astrophotographer learn when to take pictures of three distinctive Moon features. Students learn that they are most easily viewed when they are near the terminator, the border between light and dark on the Moon. This launches them into an investigation of light and dark on the Moon, which lays the foundation for learning about the mechanisms behind the Moon’s changing appearance as it is viewed from Earth.

    In Chapter 1, students work to answer the question: Why is there a border between light and dark on the Moon? Students discover that the sun illuminates half of the Moon in the same manner that it illuminates Earth, and that the half of the Moon that faces away from the sun is always dark. By the end of the chapter, students establish a fundamental grasp of how and why the Moon appears to be both light and dark.

    In Chapter 2, students investigate the question: Why does the border between light and dark on the Moon change location? By using the digital Earth, Moon, and Sun Simulation and the physical Moon Sphere Model to help with challenging spatial concepts, students find that the Moon moves into different positions around Earth on a monthly cycle, which causes the phases of the Moon to follow a consistent pattern. By the end of this chapter, students will have learned about how the orbital motion of the Moon creates the monthly pattern of moon phases that we observe from Earth.

    In Chapter 3, students work to find an answer to the question: What are the conditions that cause a lunar eclipse? By using the Moon Sphere Model, they discover that lunar eclipses are caused when Earth casts a shadow on the Moon. However, lunar eclipses do not happen every time Earth is between the Moon and the sun. By reading an article and using the Sim, students find evidence that this is due to the fact that the Moon’s orbit around Earth is not in the same plane as Earth’s orbit around the sun, which makes it unusual for Earth’s alignment to be directly in between the sun and the Moon. By the end of this chapter, students understand that a lunar eclipse is a rare event that only occurs when Earth is positioned in between the sun and the Moon, blocking the sun’s light from hitting the Moon.

    In Chapter 4, students consider a new anchor phenomenon, synthesizing what they have learned to help an artist at About Space magazine decide whether a lunar eclipse will occur in a distant planetary system with two stars. To do this, they answer the question: During a year, will there be a lunar eclipse of the moon of Kepler-47c? Students examine evidence comparing the planet Kepler 47c and its moon and stars to what they already know about Earth, the Moon, and the sun. They discuss the strength of the evidence during a Science Seminar with their peers, and by the end of the chapter they are ready to write a scientific argument supporting their ideas about the likelihood of a lunar eclipse occurring on Kepler 47c.