VISUALIZATION CLASSZONE.COM. Waxing Moon

Transcription

1 INSTRUCT Address Misconceptions IDNTIFY Ask: What causes lunar phases If students say that lunar phases are caused by arth s shadow, they may hold misconceptions about the s movements and why the shines. CORRCT Have students use models to see that half the is lit by the Sun at any given time, but only part of it may be visible from our point of view on arth. If time allows, have students record their observations of the for two s or more to see that lunar phases involve small changes from day to day. RASSSS Tell students that if phases were caused by arth s shadow, the would look the same for most of the month and not have the phases that it does. Have students demonstrate three or more phases using a model (such as that from Investigate Phases of the on p. 62). Demonstrations should include direction of sunlight and position of the relative to arth. Technology Resources Visit ClassZone.com for background on common student misconceptions. MISCONCPTION DATABAS Real World xample The month is based, historically, on the motion of the. The takes 27.3 days to go around arth. Because arth moves about 30º around the Sun during this time, the has to go somewhat more than once around arth to complete a cycle of phases, so a lunar month takes about 29 days. VISUALIZATION CLASSZON.COM xplore lunar phases. reading tip Use the red dashed lines at each position in the diagram on page 61 to determine what part of the is visible from arth. reading tip Crescent and gibbous describe the shape, while waxing and waning describe the changes growing or shrinking. 60 Unit: Space Science The s position in its monthly orbit determines how it appears from arth. The diagram on page 61 shows how the positions of the, the Sun, and arth affect the shapes you see in the sky. Waxing First Week The cycle begins with a new moon. From arth, the and the Sun are in the same direction. If you face a new moon, you face the Sun. Your face and the far side of the are in sunlight. The near side of the is unlit, so you do not see it. During a new moon, there appears to be no. As the moves along its orbit, sunlight begins falling on the near side. You see a thin crescent shape. During the first, the keeps moving farther around, so more of the near side becomes lit. You see thicker crescents as the waxes, or grows. Second Week When half of the near side of the is in sunlight, the has completed one-quarter of its cycle. The phase is called the first quarter, even though you might describe the shape as a halfmoon. You can see in the diagram that the is 90 degrees at a right angle from the Sun. If you face the first-quarter moon when it is high in the sky, sunlight will shine on the right side of your head and the right side of the. You see more of the as it moves along its orbit during the second. The phase is called gibbous (GIHB-uhs) when the near side is more than half lit but not fully lit. The is still waxing, so the phases during the second are called waxing gibbous moons. check your reading DIFFRNTIAT INSTRUCTION Why does the sometimes seem to have a crescent shape Waning Third Week Halfway through its cycle, the whole near side of the is in sunlight a full moon. You might think of it as the second quarter. Viewed from arth, the and the Sun are in opposite directions. If you face a full moon at sunset, sunlight from behind you lights the back of your head and the near side of the. As the continues around during the third, less and less of the near side is in sunlight. The seems to shrink, or wane, so these phases are called waning gibbous moons. Fourth Week When the near side is again only half in sunlight, the is three-quarters of the way through its cycle. The phase is called the third quarter. The is again 90 degrees from the Sun. If you face the third-quarter moon when it is high in the sky, sunlight will shine on the left side of your head and the left side of the. A B in sunlight Answer: that is when less than half of its near side is 60 Unit: Space Science A During which phase does the seem to disappear new moon B What happens to the during the first two s It waxes, or grows. nglish Learners This section includes sentences with a variety of introductory clauses and phrases. Point out common introductory phrases to watch for, and help students distinguish between them and the main clause, which contains the subject of the sentence. Write the following example from this page on the board. Underline the introductory phrase and circle the subject. As the moves along its orbit, sunlight begins falling on the near side.

2 Lunar Phases The appearance of the depends on the positions of the Sun,, and arth. If you could watch the from high above its pole, you would always see half the in sunlight and half in darkness. WAXING (GROWING) 2 second new moon full moon sunlight 1 first arth third 3 line of sight WANING fourth 4 (SHRINKING) View from arth Viewed from arth, the s shape seems to change first second third new moon waxing crescent first quarter waxing gibbous full moon To help students interpret the visual of lunar phases, ask: In which direction is the orbiting How do you know The orbits in a counterclockwise direction when viewed from above its north pole. The large arrows in the cycle diagram show the direction of movement. What do the dotted lines going through the drawings represent the division between the near and far sides of the During a new moon, what part of the is lit the far side Why is the phase pictured at the red 4 called third quarter even though the looks half lit The has completed the third quarter of its cycle; it is three-quarters old. Help students compare the two views of each phase. Use the white part of the near side to estimate how much of the near side should be visible in the view from arth. new, nothing visible; crescents, 1/4; quarters, 1/2; gibbous, 3/4; full, all of moon is visible waning gibbous direction from arth This lit portion is visible from arth. 4 fourth waning gibbous third quarter waning crescent Develop Critical Thinking APPLY Remind students that the is about 380,000 km, or about 30 arthdiameters, from arth. Have them use the size of arth in the diagram to estimate where the would need to be for the scale distance to be correct. Nearly half a meter from arth; students may count or may measure and calculate. COMPAR How are the sunlit portions alike in the image and the diagram of the waning gibbous moon DIFFRNTIAT INSTRUCTION Alternative Assessment Have students keep a journal for a month. They should look for the every day and night, note the date and time, and sketch the when they see it. Teams should compare their individual journals frequently and label the phases as they learn them. Chapter 2: arth,, and Sun 61 Determine why the has phases. Ask: Why does the appear to change shape Its position relative to arth and the Sun changes. Answer: Both lit portions show that three-fourths of the near side is lit. Chapter 2 61

3 INVSTIGAT Phases of the PURPOS To model phases TIPS 20 min. Darken the room before beginning this activity. Try to position the lamp as high as possible so that students heads do not block the light for a full moon. Students may need to hold the balls high. WHAT DO YOU THINK The right side of the ball was lit, because the lamp was to the right of the ball. The drawings have the same shape as the phases shown in the photographs. Step 2 resembles a waxing crescent; step 3 resembles the in first quarter; step 4 resembles a full moon, thirdquarter moon, and waning crescent. CHALLNG Sunlight reflects off arth and can then reflect off the near side of the. R Datasheet, Phases of the, p. 114 Technology Resources Customize this student lab as needed or look for an alternative. Print rubrics to assess student lab reports. Lab Generator CD-ROM Metacognitive Strategy Tell students to close their eyes and imagine they are viewing the from different places in space. What do they see How does it differ from what they see from arth What did they do to change their perspective As the continues to move around arth during the fourth, less and less of the near side is in sunlight. The waning crescent moon grows thinner and thinner. At the end of the fourth, the near side is again unlit, and the new moon begins a new cycle. Crescent and Gibbous s Think through the waxing lunar phases again. The waxes from new to crescent to gibbous during the first half of its cycle. Then it wanes from full to gibbous to crescent during the second half of its cycle. The amount of the that you see from arth depends on the angle between the and the Sun. When this angle is small, you see only a small amount of the. Crescent moons occur when the appears close to the Sun in the sky. As a result, they are visible most often in the daytime or around the time of sunrise or sunset. When the angle between the Sun and the is large, you see a large amount of the. Gibbous and full moons appear far from the Sun in the sky. You may see them in the daytime, but you are more likely to notice them at night. check your reading What shape does the appear to be when it is at a small angle to the Sun Phases of the Why does the seem to change shape PROCDUR C Place the ball on the stick, which will act as a handle. The ball will represent the, and your head will represent arth. Hold the ball toward the light, then move it to your left until you see a bright edge. Draw what you see. Move the ball farther around until half of what you see is lit. Draw it. Keep moving the ball around to your left until the side you see is fully lit, then half lit, then lit only a little bit. ach time, face the ball and draw it. WHAT DO YOU THINK In step 2, which side of the ball was lit xplain why. How are your drawings like the photographs of the s phases Label each drawing with the name of the corresponding lunar phase. CHALLNG When the is a crescent, sometimes you can dimly see the rest of the if you look closely. Where might the light that makes the darker part of the visible come from SKILL FOCUS Making models MATRIALS foam ball stick lamp TIM 20 minutes XPLOR Revisit What Makes the Bright on p. 41. Have students describe their observations. Answer: crescent 62 Unit: Space Science DIFFRNTIAT INSTRUCTION C When do you see a small amount of the when it is crescent and appears close to the Sun Below Level While doing the investigation, students may lose track of the model s orbit when they pause to do their sketches. Have them work with partners. One student can hold the ball and keep track of the step number while the other sketches; then they can switch roles. 62 Unit: Space Science

4 D Shadows in space cause eclipses. Sunlight streams past arth and the, lighting one side of each body. Beyond each body is a long, thin cone of darkness where no sunlight reaches a shadow in space. The two bodies are far apart, so they usually miss each other s shadow as the orbits arth. However, if the, the Sun, and arth line up exactly, a shadow crosses arth or the. An eclipse occurs when a shadow makes the Sun or the seem to grow dark. In a lunar eclipse, the darkens. In a solar eclipse, the Sun seems to darken. Sun arth umbra penumbra Lunar clipses The becomes dark during a lunar eclipse because it passes through arth s shadow. There are two parts of arth s shadow, as you can see in the diagram above. The umbra is the darkest part. Around it is a spreading cone of lighter shadow called the penumbra. Just before a lunar eclipse, sunlight streaming past arth produces a full moon. Then the moves into arth s penumbra and becomes slightly less bright. As the moves into the umbra, arth s dark shadow seems to creep across and cover the. The entire can be in darkness because the is small enough to fit entirely within arth s umbra. After an hour or more, the moves slowly back into the sunlight that is streaming past arth. A total lunar eclipse occurs when the passes completely into arth s umbra. If the misses part or all of the umbra, part of the stays light and the eclipse is called a partial lunar eclipse. arth s shadow VOCABULARY Remember to record vocabulary terms. The starts getting dark on one side as it passes into arth s umbra. ven when the is completely within arth s umbra, some red sunlight, bent by arth s atmosphere, may still reach the. To help students interpret the diagram of a lunar eclipse: Have them compare and contrast the arth s umbra and penumbra. Both are parts of arth s shadow. The umbra is the darkest part. The penumbra is a spreading cone of lighter shadow around the umbra. Ask: Where is arth in relation to the Sun and in between them Ask: How would the diagram change to show a partial lunar eclipse the would be only partially in arth s umbra. History of Science From ancient times, educated people have known that arth was round. The famous Greek philosopher Aristotle ( BC.) observed lunar eclipses and noted that arth s shadow on the was curved only a round object would cast a curved shadow. Later, the Greek mathematician ratosthenes measured arth s circumference by using shadows. xplain what causes eclipses. Ask: What causes eclipses A shadow makes the Sun or the seem to grow dark. Chapter 2: arth,, and Sun 63 DIFFRNTIAT INSTRUCTION D What becomes dark during a lunar eclipse the What is the darkest part of arth s shadow the umbra Advanced Have students refer back to the visual of lunar phases on p. 61. Then have them reexamine the visual of a lunar eclipse on this page. Ask: During which lunar phase or phases can a lunar eclipse occur xplain your answer. A lunar eclipse can only occur during a full moon because during that phase the Sun, arth, and the are properly lined up. R Challenge and xtension, p. 113 Chapter 2 63

5 Health Connection The retina, located near the back of the eye, is made up of two kinds of cells rods and cones. Both types are extremely sensitive to light and can be easily damaged by staring directly at the Sun. This can lead to temporary or permanent blindness. Because the retina has no pain receptors, the damage may not be apparent until several hours later. Therefore, no one should ever look directly at the Sun s disk, even when the Sun appears mostly hidden during a solar eclipse. F Solar clipses In a solar eclipse, the Sun seems to darken because the s shadow falls onto part of arth. Imagine that you are in the path of a solar eclipse. At first, you see a normal day. You cannot see the dark moving toward the Sun. Then part of the Sun seems to disappear as the moves in front of it. You are in the s penumbra. After several hours of growing darkness, the covers the Sun s disk completely. The sky becomes as dark as night, and you may see constellations. In place of the Sun is a black disk the new moon surrounded by a pale glow. You are in the s umbra, the darkest part of the shadow, experiencing a total solar eclipse. After perhaps a minute, the Sun s bright surface starts to appear again. To help students interpret the diagram of a solar eclipse, ask: In what phase is the during a solar eclipse new moon This diagram and the one on p. 63 both say. How would the diagrams be different if they were to scale Could they be shown in this book The Sun would be much larger and the distances between the Sun and arth and between the and arth would be much greater, too great to fit in this book. Teach Difficult Concepts Students may question why eclipses do not happen every month. xplain that the s orbit is slightly tilted with respect to arth s orbit around the Sun. Most times, the is not in the same plane as arth s orbit. Both solar and lunar eclipses can only occur when the Sun, the, and arth are aligned. June 21, 2001 clipse total eclipse Sun umbra penumbra arth A solar eclipse occurs when the passes directly between arth and the Sun. As you can see in the diagram above, the side of the that faces arth is unlit, so solar eclipses occur only during new moons. If you could watch a solar eclipse from space, it might seem more like a lunar eclipse. You would see the s penumbra, with the dark umbra in the center, move across arth s daylight side. However, the is smaller than arth, so it casts a smaller shadow. As you can see in the diagram above, the s umbra covers only a fraction of arth s surface at a time. path of penumbra path of umbra G In this time-lapse photograph, the Sun s disk appears darker as the passes in front. When the is exactly in front of the Sun, the sky grows as dark as night. Path of June 21, 2001 clipse Only locations along the thin central path of the shadow experience a total eclipse. Other locations experience a partial eclipse. 64 Unit: Space Science DIFFRNTIAT INSTRUCTION F What casts a shadow on arth during a solar eclipse the G Why does the cast a smaller shadow than arth The is smaller. Below Level Place students into groups of three. One student should represent the Sun, another should represent arth, and the third should represent the. Have the students line up in proper order to model the positions of the Sun, arth, and during both a lunar and a solar eclipse. Students representing the and arth can use their arms to represent the edges of their shadows. During a lunar eclipse, arth is between the Sun and the. During a solar eclipse, the is between the Sun and arth. 64 Unit: Space Science

6 H Only locations in the path of the s shadow experience a solar eclipse. Some people travel thousands of miles to be in the thin path of the s umbra so that they can experience a total solar eclipse. Locations near the path of the umbra get an eclipse that is less than total. If only the penumbra moves over your location, you experience a partial solar eclipse. The covers just part of the Sun. Bright light from the Sun s disk can damage your eyes if you look directly at it. The Sun is unsafe to look at even when the covers most of the Sun s disk. If you have the chance to experience a solar eclipse, use a safe method to view the Sun. Check Your Reading Where is the during a solar eclipse Find a way to remember the difference between the two types of eclipses. The s gravity causes tides on arth. If you have spent time near an ocean, you may have experienced the usual pattern of tides. At first, you might see dry sand that slopes down to the ocean. Then, waves creep higher and higher onto the sand. The average water level rises slowly for about 6 hours. The highest level is called high tide. Then the water level slowly drops for about 6 hours. The lowest level is called low tide. Then the water level rises and falls again. The entire pattern two high tides and two low tides takes a little more than 24 hours. Check Your Reading How many high tides do you expect per day Tides occur because the s gravity changes the shape of arth s oceans. The pulls on different parts of arth with different amounts of force. It pulls hardest on the side of arth nearest it, a little less hard on the center of arth, and even less hard on the farthest side of arth. If arth were flexible, it would be pulled into a football shape. arth s crust is hard enough to resist being pulled into a different shape, but arth s oceans do change shape. COMBINATION NOTS Remember to make notes about new ideas. In areas with tides, the water generally reaches its lowest level twice a day and its highest level twice a day. Real World xample There are safe ways to view a solar eclipse. One method is pinhole projection. Use a pin to poke a small hole in the center of a large piece of cardboard. Outside, stand on a smooth surface. Hold the cardboard at shoulder height and look at the middle of the cardboard s shadow to see the image of the round or partially eclipsed Sun. More complex arrangements, also suitable for viewing sunspots, can be found in libraries and on the Internet. Specially designed glasses can also be used to view solar eclipses. These glasses are covered with a thin film of aluminum or a similar substance that filters out the Sun s harmful rays. To help students interpret the two photographs of the tides, ask: What is the main difference between these two photographs The water covers the shore in the bottom photograph. Which photograph shows high tide the bottom photograph What helps you tell about how high the tide is in this inlet The people in the top photograph provide a scale. Answer: The is between the Sun and arth. Students may suggest remembering that the name of the eclipse describes the object that darkens or seems to disappear. Answer: two Chapter 2: arth,, and Sun 65 DIFFRNTIAT INSTRUCTION H Why do tides occur because the s gravity changes the shape of arth s oceans Alternative Assessment Tell students that tidal range refers to the difference in water level between high tide and low tide. Have them obtain tide data from the Internet or from a newspaper located in a coastal area. The tide data (a table or graph) should show water levels for a tidal day, which corresponds to slightly more than 24 hours. Have students describe any patterns they observe. Students should note that over the course of most tidal days, there are two peaks, or high tides, and two troughs, or low tides. Chapter 2 65

7 xplain why arth s oceans have tides. Ask: What effect does the have on arth s oceans It produces two bulges of water. rotation. Answer: It takes 24 hours for arth to complete one Real World xample The tidal range the difference in water level between high tide and low tide depends partly on the shape of the shoreline. The range is highest in small, narrow inlets. At the narrow end of Nova Scotia s long, V-shaped Bay of Fundy, for example, high tide is as much as 15 meters above low tide. Reinforce Have students relate the section to the Big Idea. R Reinforcing Key Concepts, p. 115 RSOURC CNTR CLASSZON.COM Learn more about tides. Cause of Tides The s gravity changes the shape of arth s oceans. low tide high tide rotation of arth The diagram above shows what would happen if arth were covered with a thick layer of water. The s pull produces a bulge of thicker ocean water on the side of arth nearest the. Another bulge of water is produced on the side of arth farthest from the because the pulls the center of arth away from that side. The layer of water is thinnest in the middle, between the bulges. A location moves past different thicknesses of water as arth turns on its axis. As a result, the water level there rises and falls. The thickest water produces the highest level, which is high tide. A quarter of a rotation 6 hours later, the location has moved to the thinnest layer of water, or low tide. Another high tide and low tide complete the cycle. Because the is orbiting while arth is turning, the cycle takes a little longer than the 24 hours in a day. Check Your Reading Why does a cycle of tides take about 24 hours Assess A Reteach ASSSS & RTACH Section 2.3 Quiz, p. 25 Place students in groups of three two to represent arth and the, and one to keep track of where sunlight falls. Students should imagine sunlight coming from one wall of the classroom. Have the teams model the positions that produce different lunar phases. Positions should match the diagram on p. 61. Students may use a piece of cloth to cover the unlit half of the. Technology Resources Have students visit ClassZone.com for reteaching of Key Concepts. CONTNT RVIW CONTNT RVIW CD-ROM KY CONCPTS 1. When the is full, where is it in its orbit around arth 2. Where is the in its orbit at the time of a solar eclipse 3. If it is high tide where you are, is the tide high or low on the side of arth directly opposite you 66 Unit: Space Science ANSWRS 1. The full moon is opposite the Sun from arth. 2. The is in front of the Sun. CRITICAL THINKING 4. Apply If you were on the s near side during a new moon, how much of the side of arth facing you would be sunlit 5. Predict If arth did not turn, how would the pattern of tides be affected 3. The tide is high. 4. All of the side of arth facing the would be sunlit. CHALLNG 6. Predict Would we see lunar phases if the did not rotate while it orbits arth 5. A cycle of tides would take about a month, rather than a day. Students may reasonably predict unchanging water heights. 6. Yes; lunar phases would occur regardless of the s period of rotation. 66 Unit: Space Science