The Sun-Earth- Moon System

1 The Sun-Earth- moon SystemFull moon Rising The Real StoryWhy does the moon s appearance change throughout the month?Do the Sun and moon really rise? You will find the answers tothese questions and also learn why we have summer and or revolution which motion of earth brings morningand which brings summer? Science JournalMany common observations,such as seasons, eclipses,and lunar phases, are causedby interactions between theSun, earth , and the 1 EarthMain IdeaEarth is asphere that rotates on atilted axis and revolvesaround the 2 The moon earth s SatelliteMain IdeaEclipses andphases of the moon occur asthe moon moves in relationto the Sun and 3 Exploring earth s MoonMain IdeaKnowledge of the moon s structureand composition has been increased by manyspacecraft missions to the Ehlers/Stone/Getty ImagesEarth and the MoonAll onEarth can see and feel the move-ments of earth and the moon asthey circle the Sun.

2 Make the following Foldableto organize what you learn about these move-ments and their sheet of paper in half cm from the top.(Hint: From the tip ofyour index finger toyour middle knuckleis about cm.)Open and drawlines along in a TableAs you read the chapter,summarize the movements of earth and theMoon in the left column and the effects of thesemovements in the right 3 STEP 2 STEP 1 Model Rotation and RevolutionThe Sun rises in the morning; at least, itseems to. Instead, it is earth that moves. Themovements of earth cause day and night, aswell as the seasons. In this lab, you willexplore earth s a basketball with one finger at thetop and one at the bottom. Have a class-mate gently spin the how this models earth s to hold the basketball and walkone complete circle around anotherstudent in your does this model earth s revolution?

3 CriticallyWrite a paragraph inyour Science Journal describing how thesemovements of the basketball modelEarth s rotation and revolution. Start-Up ActivitiesPreview this chapter s contentand activities at Ehlers/Stone/Getty Images40 A uJCHAPTER 2 The Sun-Earth- moon SystemApply It!Practice summarizingas you read this chapter. Stop after each section and write a brief It!Summarizing helps you organize information,focus on main ideas, and reduce the amount of information to summarize, restate the important facts in a short sentence or para-graph. Be brief and do not include too many It!Read the text on page 44 labeled read the summary below and look at the important facts from that solstice is the day whenthe Sun reaches its greatestdistance north or south ofthe FactsIn the northern hemisphere,the summer solstice occurs inJune, and the winter solsticeoccurs in the southern hemisphere,the winter solstice occurs inJune, and the summer solsticeoccurs in solstice is about thelongest period of daylight ofthe solstice is about theshortest period of daylight ofthe BBefore You ReadStatementAfter You ReadA or DA or D1 earth s revolution around the Sun causes dayand night to s magnetic poles are aligned on earth srotational occurs in the northern hemispherewhen earth is closest to the an equinox.

4 The number of daylighthours is nearly equal with the number of night-time hours all over the observing the phases of the moon , theMoon s lighted surface area is daylight on the Moonand the dark portion is nighttime on the length of one moon day is about the sameamount of time as the length of one earth lunar eclipse occurs when the moon comesbetween earth and the first walked on the moon during theApollospacecraft out a worksheetof this page at your summary to make sure you didn t change the author s original meaning or this to focus on the main ideas as you read the you readthe chapter, respond to the statements below on your worksheet or on a numbered sheet of paper. Write an Aif you agreewith the statement. Write a Dif you disagreewith the you readthe chapter, look back to this page to see if you vechanged your mind about any of the statements.

5 If any of your answers changed, explain why. Change any false statements into true statements. Use your revised statements as a study of earth You awaken at daybreak to catch the Sun rising from thedark horizon. Then it begins its daily journey from east to westacross the sky. Finally the Sun sinks out of view as night the Sun moving or are you?It wasn t long ago that people thought earth was the centerof the universe. It was widely believed that the Sun revolvedaround earth , which stood still. It is now common knowledgethat the Sun only appears to be moving around earth . BecauseEarth spins as it revolves around the Sun, it creates the illusionthat the Sun is moving across the mistaken idea about earth concerned its as recently as the days of Christopher Columbus, manypeople believed earth to be flat.

6 Because of this, they were afraidthat if they sailed far enough out to sea, they would fall off theedge of the world. How do you know this isn t true? How havescientists determined the true shape of earth ?Spherical ShapeA round, three-dimensional object is calledasphere(SFIHR). Its surface is the same distance from its cen-ter at all points. Some common examples of spheres are basket-balls and tennis the late twentieth century, artificial satellites and spaceprobes sent back pictures showing that earth is earlier, Aristotle, a Greek astronomer and philosopherwho lived around 350 , suspected that earth was observed that earth cast a curved shadow on the Moonduring an addition to Aristotle, otherindividuals made observationsthat indicated earth s sphericalshape.

7 Early sailors, for example,noticed that the tops of ap-proaching ships appeared first onthe horizon and the rest appearedgradually, as if they were comingover the crest of a hill, as showninFigure s rotationand causes seasonsto life follows the rhythm ofEarth s Vocabularyorbit:the path taken by an objectrevolving around anotherNew Vocabulary sphere ellipse axis solstice rotation equinox revolutionEarthFigure 1 For many years, sailorshave observed that the tops ofships coming across the horizonappear first. This suggests thatEarth is spherical, not flat, as wasonce widely EvidenceSailors also noticed changes in how thenight sky looked. As they sailed north or south, the North Starmoved higher or lower in the sky.

8 The best explanation was aspherical , most people know that earth is spherical. They alsoknow all objects are attracted by gravity to the center of a spher-ical earth . Astronauts have clearly seen the spherical shape ofEarth. However, it bulges slightly at the equator and is somewhatflattened at the poles, so it is not a perfect s axisis the imaginary vertical line aroundwhich earth spins. This line cuts directly through the center ofEarth, as shown in the illustration accompanying Table are located at the north and south ends of earth s axis. Thespinning of earth on its axis, called rotation,causes day and nightto occur. Here is how it works. As earth rotates, you can see theSun come into view at daybreak.

9 earth continues to spin, makingit seem as if the Sun moves across the sky until it sets at night, your area of earth has rotated so that it is facingaway from the Sun. Because of this, the Sun is no longer visible toyou. earth continues to rotate steadily, and eventually the Suncomes into view again the next morning. One complete rotationtakes about 24 h, or one day. How many rotations does earth com-plete during one year? As you can infer from Table 1,it completesabout 365 rotations during its one-year journey around the does the Sun seem to rise and set?AxisTable 1 Physical Properties of EarthDiameter (pole to pole) 12,714 kmDiameter (equator) 12,756 kmCircumference (poles) 40,008 kmCircumference (equator) 40,075 kmMass 3 1024 kgAverage density g/cm3 Average distance to the Sun 149,600,000 kmPeriod of rotation (1 day) 23 h, 56 minPeriod of revolution (1 year) 365 days, 6 h, 9 minEarth s RotationSuppose that earth srotation took twice aslong as it does now.

10 Inyour Science Journal, pre-dict how conditions suchas global temperatures,work schedules, plantgrowth, and other factorsmight change underthese circumstances. SECTION 1 EarthJu41 Rotation42uJCHAPTER 2 The Sun-Earth- moon SystemMagnetic FieldScientists hypothesize that the movementof material inside earth s core, along withEarth s rotation, generates a magnetic field. This magnetic fieldis much like that of a bar magnet. earth has a north and a southmagnetic pole, just as a bar magnet has opposite magnetic polesat each of its ends. When you sprinkle iron shavings over a barmagnet, the shavings align with the magnetic field of the mag-net. As you can see in Figure 2, earth s magnetic field issimilar almost as if earth contained a giant bar s magnetic field protects you from harmful solar radiationby trapping many charged particles from the AxisWhen you observe a compass needle point-ing north, you are seeing evidence of earth s magnetic s magnetic axis, the line joining its north and south mag-netic poles, does not align with its rotational axis.