CS_Ch12_ClimateChange 3/1/2005 4:56 PM Page 761 Activity 3 How Do Earth’s Orbital Variations Affect Climate? Activity 3 How Do Earth’s Orbital Variations Affect Climate? Goals Think about It In this activity you will: When it is winter in New York, it is summer in Australia. • Understand that Earth has an axial tilt of about 23 1/2°. • Why are the seasons reversed in the Northern and • Use a globe to model the Southern Hemispheres? seasons on Earth. • Investigate and understand What do you think? Write your thoughts in your EarthComm the cause of the seasons in notebook. Be prepared to discuss your responses with your small relation to the axial tilt of group and the class. the Earth. • Understand that the shape of the Earth’s orbit around the Sun is an ellipse and that this shape influences climate. • Understand that insolation to the Earth varies as the inverse square of the distance to the Sun. 761 Coordinated Science for the 21st Century CS_Ch12_ClimateChange 3/1/2005 4:56 PM Page 762 Climate Change Investigate Part A: What Causes the Seasons? Now, mark off 10° increments An Experiment on Paper starting from the Equator and going to the poles. You should have eight 1. In your notebook, draw a circle about marks between the Equator and pole 10 cm in diameter in the center of your for each quadrant of the Earth. Use a page. This circle represents the Earth. straight edge to draw black lines that Add the Earth’s axis of rotation, the connect the marks opposite one Equator, and lines of latitude, as another on the circle, making lines shown in the diagram and described that are parallel to the Equator. below. Label the Northern and This will give you lines of latitude in Southern Hemispheres. 10° increments so you can locate your latitude fairly accurately. Note 23.5˚ that the lines won’t be evenly spaced from one another because latitude is measured as an angle from the center Equator of the Earth, not a linear distance. Northern Hemisphere plane of 2. Imagine that the Sun is directly on orbit the left in your drawing. Draw horizontal arrows to represent incoming Sun rays from the left side of the paper. rotation axis Southern Hemisphere 3. Assume that it is noon in your community. Draw a dot where your Put a dot in the center of the circle. community’s latitude line intersects Draw a dashed line that goes directly the perimeter of the circle on the left. up and down from the center dot to This dot represents your community. the edge of the circle. Use a protractor to measure 23 1/2° from a) Explain why this represents noon. this vertical dashed line. Use a blue b) At any given latitude, both north pen or pencil to draw a line through and south, are the Sun’s rays the center of the “Earth” at 23 1/2° striking the Northern Hemisphere to your dashed line. This blue line or the Southern Hemisphere at a represents the Earth’s axis of rotation. larger angle relative to the plane Use your protractor to draw a red of orbit? line that is perpendicular to the axis and passes through the center dot. c) Which do you think would be This red line represents the Equator warmer in this drawing—the of the Earth. Label the Northern and Northern Hemisphere or the Southern Hemispheres. Next you Southern Hemisphere? Write need to add lines of latitude. To do down your hypothesis. Be sure to this, line your protractor up with the give a reason for your prediction. dot in the center of your circle so that d) What season do you think this is it is parallel with the Equator. in the Northern Hemisphere? 762 EarthComm CS_Ch12_ClimateChange 3/1/2005 4:56 PM Page 763 Activity 3 How Do Earth’s Orbital Variations Affect Climate? 4. Now consider what happens six 3. Position the globe so that its axis is months later. The Earth is on the tilted 23 1/2° from the vertical, and the opposite side of its orbit, and the North Pole is pointed in the direction sunlight is now coming from the of the light source. right side of the paper. Draw 4. Turn on the light source. horizontal arrows to represent incoming Sun’s rays from the right. a) Record the initial temperature. Then record the temperature on the 5. Again, assume that it is noon. Draw thermometer every minute until the a dot where your community’s temperature stops changing. latitude line intersects the perimeter of the circle on the right. 5. Now position the globe so that the axis is again tilted 23 1/2° from the a) Explain why the dot represents vertical but the North Pole is pointing your community at noon. away from the light source. Make b) Are the Sun’s rays striking the sure the light source is the same Northern Hemisphere or the distance from the globe as it was in Southern Hemisphere more Step 4. Turn on the light source again. directly? a) Record the temperature every c) Which do you think would be minute until the temperature stops warmer in this drawing—the changing. Northern Hemisphere or the 6. Use your observations to answer the Southern Hemisphere? Why? following questions in your d) What season do you think this is notebook: in the Northern Hemisphere? a) What is the difference in the average temperature when the Part B: What Causes the Seasons? An North Pole was pointing toward Experiment with a Globe your “community” and when it 1. Test the hypothesis you made in Part A was pointing away? about which hemisphere would be b) What caused the difference in warmer in which configuration. temperature? Find your city on a globe. Using duct tape, tape a small thermometer on it. The duct tape should cover the thermometer bulb, and the thermometer should be over the city. With a permanent black marking pen, color the duct tape black all over its 2 m surface. 2. Set up a light and a globe as shown. Use only alcohol thermometers. Place a soft cloth on the table under the thermometer in case it falls off. Be careful not to touch the hot lamp. 763 Coordinated Science for the 21st Century CS_Ch12_ClimateChange 3/1/2005 4:57 PM Page 764 Climate Change Part C: What Would Happen if the 2. Repeat the experiment you did in Earth’s Axial Tilt Changed? An Part A, except this time use an axial Experiment on Paper tilt of 35°. 1. Repeat the experiment you did in a) Compared to an axial tilt of Part A, except this time use an axial 23 1/2°, would your hemisphere tilt of 10°. experience a warmer or colder winter? a) Compared to an axial tilt of 23 1/2°, would your hemisphere b) Compared to an axial tilt of experience a warmer or colder 23 1/2°, would your hemisphere winter? experience a hotter or cooler summer? b) Compared to an axial tilt of 23 1/2°, would your hemisphere experience a hotter or cooler summer? Part D: The Earth’s Elliptical Orbit 3. Stretch out the rope from the dowel around the Sun until it is tight, and hold a piece of chalk at the bend in the rope, as 1. Tie small loops in each end of a rope, shown in the diagram below. While as shown in the diagram above. holding the chalk tight against the 2. Pick a point in about the middle of rope, move the chalk around the the floor, and put the two loops dowel. together over the point. Put a dowel a) What type of figure have you vertically through the loops, and constructed? press the dowel tightly to the floor. 764 EarthComm CS_Ch12_ClimateChange 3/1/2005 4:57 PM Page 765 Activity 3 How Do Earth’s Orbital Variations Affect Climate? 4. Draw a straight line from one edge b) What would be the shape of the of the circle that you just made to curve when the dowel points are the opposite edge, through the spaced a distance apart that is just center of the circle. This line equal to the length of the rope represents the diameter of the circle. between the two loops? Mark two points along the diameter, each a distance of 20 cm from the Part E: How Energy from the Sun Varies center of the circle. Put the loops of with Distance from the Sun the rope over the two points, hold them in place with two dowels, and 1. Using scissors and a ruler, cut out a use the chalk to draw a curve on square 10 cm on a side in the middle one side of the straight line. Move of a poster board. the chalk to the other side of the 2. Hold the poster board vertically, line and draw another curve. parallel to the wall and exactly two a) What type of figure have you meters from it. constructed? 3. Position a light bulb along the imaginary horizontal line that passes dowels from the wall through the center of rope the hole in the poster board. See the 20 cm diagram. center chalk poster board 10 cm x 10 cm major axis minor axis 2 m 2 m 5. Using different colors of chalk, make a few more curved figures in the same way. Choose sets of dowel points that are farther and farther away from the center.