Earth’s Motions Lab 4‐3 Ellipses

Name___________________________________ Partner__________________________________ Astronomy Block_______ Date_________________ TOPIC IV: Earth’s Motions LAB 4‐3: ELLIPSES INTRODUCTION: The earth revolves around the sun in a geometrically shaped orbit called an ellipse. An ellipse has two “center points”. Each one is called a focus. The sun is not in the exact middle of the earth’s orbit, rather, it is found at one of the focal points. OBJECTIVE: You will be able to compare the shape of the earth’s orbit and orbits of other planets with the shape of a circle. Focus 1 Focus 2 d (Distance) L (major axis) VOCABULARY: 1. Ellipse: 2. Eccentricity: 3. Focus (plural is foci): 4. Major axis: 5. Circle: PROCEDURE: 1. 2. 3. 4. Cut a piece of string about 22‐28 cm in length and tie the ends together to form a loop. On a plain white paper draw a straight line lengthwise down the middle of the paper. Near the center of this line, draw two dots 3cm apart. Placing the paper on a piece of cardboard put a thumbtack in each dot (focus). Page | 1 5. Loop the string around the thumbtacks and draw the ellipse by placing your pencil inside and drawing around in a circular motion. 6. Label this ellipse #1. 7. Measure the distance between the thumbtack holes (foci). This is “d”. Record this on your Report Sheet. 8. Measure the length of the major axis (L) and record this on the Report Sheet. 9. Move one tack out another cm and center the tacks and draw a new ellipse. Label it #2 and measure and record d and L. 10. Move one tack out another cm and center the tacks and draw another ellipse. Label it #3 and measure and record d and L. 11. Move one tack out another cm and center the tacks and draw another ellipse. Label it #4 and measure and record d and L. 12. Place a dot in the middle of the first two foci. Using one thumb tack, construct a circle. The one thumb tack will be the radius of the circle you are to draw. 13. Using the Given equation, calculate the eccentricity (e) of each of the five figures. Show all work on you Report Sheet. ݁ൌ ݀ ‫ܮ‬ ECCENTRICITIES OF THE PLANETS Page | 2 PLANET ECCENTRICITY Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto 0.206 0.007 0.017 0.093 0.048 0.056 0.047 0.008 0.247 REPORT SHEET Note: Eccentricities may vary from student to student depending on where they tied the knot for the loop. However the eccentricities should be close to these values. Ellipse #1 Calculations d=_____________ L=_____________ e=_____________ Ellipse #2 Calculations d=_____________ L=_____________ e=_____________ Ellipse #3 Calculations d=_____________ L=_____________ e=_____________ Ellipse #4 Calculations d=_____________ L=_____________ e=_____________ Ellipse #5 (circle) d=_____________ L=_____________ e=_____________ Page | 3 Calculations DISSCUSION QUESTIONS: (Answer in Complete Sentences) 1. What change takes place in the eccentricity of the ellipses when you increase the distance between the foci? 2. Which of the four ellipses you drew (not counting the circle) was the most eccentric? 3. Which of the four ellipses you drew (not counting the circle) was the least eccentric? 4. What is the minimum eccentricity an ellipse can have? 5. What is the name of the geometric figure which has the minimum eccentricity? 6. How does the numerical value of “e” change as the shape of the ellipse approaches a straight line? 7. Where is the sun located on a diagram of the earth’s orbit? 8. What was the eccentricity you calculate for Ellipse #1? 9. Which is rounder (less eccentric), the orbit of Earth or your Ellipse #1? 10. In the table, Eccentricities of the Planets, the planets are listed in order by their distance from the sun. Is there a direct relationship between the eccentricity of its orbit and the distance a planet is from the sun? 11. List the planets in order of the increasing eccentricity of their orbits. CONCLUSION: Describe the true shape of earth’s orbit? Page | 4