LADA Studying the Phases of the Moon

Name Date Section O ACTIVITY 4 Studying the Phases of the Moon Learning Goals Understanding the phases of the Moon requires visualizing the Earth-Moon-Sun system in three dimensions. In this activity, you will develop this ability by learning how to 1. successfully replicate the motions of the Earth and Moon, as well as their positions with respect to the Sun at each lunar phase. 2. explam the continuity of the Moon phases worldwnde 3. use an Earth-Moon figure to disprove a common misconception that Moon phases are caused by Earth’s shadow. 4. correctly order the phases of the Moon. Key terms: rotate, revolve, new Moon, waxing crescent, first quarter Moon, waxing gibbous, full Moon, waning gibbous, third quarter Moon, waning crescent Step 1—Background The Earth, Moon, and Sun form an interconnected, moving system. The Earth rotates on its axis while it revolves around the Sun, which is also rotating. The Moon rotates on its axis, once for - each time it revolves around the Earth. You may better understand the phrase “revolves around” if you replace it with “orbits.” Stating “The Moon rotates around the Earth” or “The Earth rotates around the Sun” is incorrect. Perhaps you have been taught about the phases of the Moon and how those phases depend on the Earth-Moon-Sun relative positions and our view of the Moon at each of those positions. Maybe you had to memorize the names of the phases—new Moon, waxing crescent, first quarter Moon, waxing gibbous, full Moon, waning gibbous, third quarter Moon, waning crescent. This activity should lead you to a better understanding of the cause of the phases of the Moon. 1. Complete the following statements using revolves or rotates. ® The Earth once every 24 hours. ¢ The Moon once on its axis for every revolution around Earth. ® One year is the amount of time it takes Earth to around the Sun. ¢ The Moon around the Earth in approximately 29.5 days. Step 2—The Continuity of the Phases of the Moon You will use a model of the Earth-Moon system to explore the phases of the Moon as they are seen on Earth every day. Take a full sheet of paper and crush it into a ball to represent Earth. Next, take one-quarter of a sheet of paper and crush it into a smaller ball to represent the Moon. You will start with 2 new Moon, the same geometry as shown in Figure 4.1. The Moon moves nearly 12° in its orbit every 24 hours (360° divided by a rounded-off 30 days in a month). For simplicity, consider all locations to mean those for viewers in the Northern Hemisphere—those who see the Moon located in the southern part of the sky as it crosses the meridian. © 2019 by W. W. Norton & Company, Inc. Learning Astronomy by Doing Astronomy Second Edition 17

18 ACTIVITY 4 e Studying the Phases of the Moon e Parallelight “Crushed paper’ Earlh ; rays from the Sun :A7> “Grushed paper” Moon = = FIGURE 4.1 Place the models of the Earth and the Moon on Figure 4.2, found in the appendix. Imagine the sunlight coming from the front of the classroom. Orient your paper so that the “Day 0 & 30” location on the graph is toward the “Sun.” Set Earth on the center of the polar graph, and then place the Moon around the edge of the polar graph in the position of new Moon. Make Earth rotate through 1 day while moving the Moon in its orbit (revolving) 12° during each day. 2. Starting with a new Moon, rotate the paper Earth once. For this model, do all locations on Earth see approximately a new Moon (that is, if we could actually “see”a new Moon)? Circle Yes or No 3. Each time Earth rotates, 1 day passes, and the Moon moves 12°. Move the Moon counter- clockwise in its orbit, and rotate Earth once. Repeat this process (move the Moon 12° in its orbit, and rotate Earth once) until first quarter Moon (7.5 rotations of Earth). Do all locations on Earth see close to a first quarter Moon, over the course of one rotation of Earth? Circle Yes or No 4. Move the Moon and rotate Earth until the alignment is Sun-Earth-Moon (Moon on the “Day 15” mark). What is the phase of the Moon? 5. Do all locations on Earth see this phase, or very close to this phase, over the course of one rotation of Earth? Circle Yes or No 6. Continue another 7.5 days. What is the phase of the Moon? 7. Do all locations on Earth see close to this phase, over the course of one rotation of Earth? Circle Yes or No 8. Briefly summarize your answers for questions 17, explaining how the phases of the Moon are similar for all locations on Earth over the course of one Earth rotation, throughout the time the Moon revolves. By doing so, you will also show that the phases of the Moon are continuous. Step 3—Phases and Earth’s Shadow A common misconception is that the phases of the Moon are caused by Earth’s shadow. Figure 4.3 depicts the orbit of the Moon around Earth. The orbit is shown in perspective, from an angle between edge-on and directly above the orbit. The Sun is far off the paper to the left. Earth's shadow is shown to scale. The plane of the Moon's orbit is tilted with respect to the plane of Earth’s orbit. Twice per year, the Moon is in the plane of Earth’s orbit AT THE SAME TIME that it is in new or full phase. It is at these times that eclipses can happen. Otherwise, eclipses cannot occur because the shadow of Earth is above or below the Moon. © 2019 by W. W. Norton & Company, Inc. Learning Astronomy by Doing Astronomy Second Edition

20 ACTIVITY 4 e Studying the Phases of the Moon Step 4—Understanding the Order of Moon Phases 12. In Figure 4.6, the phases of the Moon are shown in random order. Starting with “k,” which represents a new Moon, sort the phases in the order they would occur, from new Moon to full Moon and back to new again. Write the corresponding letters in order below. k k (e) U] (9) (h) (i) [0} (k) FIGURE 4.6 Step 5—Putting It Together 13. Summarize what you have learned about the phases of the Moon, using at least three of the key terms introduced in the learning goals. © 2019 by W. W. Norton & Company, Inc. Learning Astronomy by Doing Astronomy Second Edition