Exploring more with seasons Name: Block

Transcription

1 Exploring more with seasons Name: Block Understanding Latitude of the Noon Sun The position of the Sun in the sky changes during the year as Earth orbits the Sun on its tilted axis. This causes a change in the angle of the Sun's rays as they strike different parts of Earth's surface, resulting in differences in intensity of incoming solar radiation (INSOLATION). Where the sun is positioned directly overhead, 90 o above the horizon (ZENITH), incoming rays strike the surface at right angles and insolation is most intense. When the sun is lower in the sky, the rays strike the surface at a lower angle and energy is spread out over a larger surface area, reducing its intensity. The latitude where the sun is at zenith changes throughout the year: the Equator on the Vernal Equinox, the Tropic of Cancer on the Summer Solstice, back to the Equator on the Autumnal Equinox, and the Tropic of Capricorn on the Winter Solstice. Latitudes north of the Tropic of Cancer and south of the Tropic of Capricorn never see the sun at zenith. Seasonal variations in temperature at any latitude on Earth's surface are determined by the angle of insolation and the number of daylight hours received during a given season. Tropical regions experience the most direct insolation throughout the year and therefore have the least seasonal variations and warmest temperatures. Polar regions experience the most indirect insolation throughout the year and have the coolest temperatures, even in seasons when they receive 24 hours of daylight. This exercise is intended to emphasize the changing position of the Sun throughout the year. Carefully follow the instructions to label the map and then answer the questions. A. On the world map, use a single colored pencil to trace each of the following lines of latitude: Equator (0 o ), Tropics of Cancer (23.5 o N) and Capricorn (23.5 o S), and the Arctic (66.5 o N) and Antarctic (66.5 o S) Circles. Label the names of latitude lines. B. Look at the pattern of months and days that occur between the tropics where it says noon sun at zenith on Based on the pattern infer the dates for 10 o S and 20 o S. Then write the following statements along their latitude line on the map: On 10 o S latitude: Noon sun at zenith on and. On 20 o S latitude: Noon sun at zenith on and. C. Write the following statements across the latitudes BETWEEN the Tropic of Cancer and the Arctic Circle: "Noon sun always in SOUTHERN sky. Sun highest on June 21 & lowest on Dec. 21." Write a similar statement to the one above across the latitudes BETWEEN the Tropic of Capricorn and the Antarctic Circle, but CHANGE IT to meet the conditions in the Southern Hemisphere. D. Write the following statement NORTH of the Arctic Circle: "24 hrs of daylight on June 21; 24 hrs of darkness on Dec. 21." Write a similar statement SOUTH of the Antarctic Circle, but CHANGE IT to meet the conditions in the Southern Hemisphere.

2 Use your map to answer the following questions. Answer questions 1 through 4 for the latitude at Lincoln-Sudbury Regional High School, approximately 42 o North. 1. Does the noon sun ever reach zenith in Massachusetts? Why or why not? 2. In which direction must we look to see the noon sun throughout the year? 3. During what season is the noon sun highest in OUR sky? During what season is the noon sun lowest in OUR sky? 4. How does the sun's height in the sky affect our seasonal temperatures? Explain your answer in detail based on what you learned in this exercise and what you have learned about direct and indirect rays. 5. If you lived in Sydney, Australia (latitude 33.5ºS), which way would you have to look to see the noon sun? On which day of the year would Sydney have the greatest number of daylight hours and see the noon sun highest in the sky? 6. Which of the following places could you visit if you wanted to see the noon sun directly overhead (or close to it) on the Vernal Equinox? Circle your answer. a. Rio de Janeiro, Brazil (23ºS) b. Taipei, Taiwan (25ºN) c. Galapagos Islands (1ºS) d. Barrow, Alaska (71ºN) 7. It is Oct 26. Where would you need to be to view the noon sun at zenith? 8. It is May 1. Between what two latitudes would you see the noon sun directly overhead? 9. If you lived at 15 degrees S, on approximately which two dates could you expect to experience the most direct rays? 10. Answer with a range of months: If you lived at the Equator, during which months would you have to look to the northern sky to see the noon sun? 11. For today s date at approximately what latitude would you expect to find direct rays? 12. At which of the following latitudes would you experience the most hours of daylight on Feb 1? a N b S c N d S

3 13. North of what latitude in the Northern Hemisphere is it possible to have 24 hours of daytime OR 24 hours of nighttime? Explain why this is possible. 14. Why is it possible for the poles to have permanent ice caps even though they have six months of sunlight each year? Hint: go back and read the introduction to this lab. Apparent Size of the Sun When you see things far away, they appear smaller and when you are closer to them, they appear larger. Likewise the apparent size or apparent diameter (how big it seems to be from your point of view) of objects in the sky depends upon your distance away from them. Since Earth makes an elliptical path around the Sun, there are certain times of the year that it will appear larger than others due to our change in proximity to the Sun. Is this change in distance a cause of seasons? Your task is to compare the apparent diameter of the Sun over the course of a year to determine if there is a relationship or not between the distance to the Sun and the seasons of the year. Apparent diameters are measured in degrees. If you had an imaginary circle between you and the object, with the radius of that circle equal to the distance between you, the apparent diameter describes how many degrees of that imaginary circle the object takes up. If you were to hold out your fist at arm s length, it would have an apparent diameter of about 10 degrees. The apparent diameter of the Sun (which in reality is much bigger than your fist) has an apparent diameter of less than 1 degree because it is so far away, making it seem very small. Units smaller than degrees are measured in minutes ( ) and seconds ( ). There are 60 seconds that make up a minute and 60 minutes that make up 1 degree. The attached graph shows the Sun s apparent diameter over the course of a year in terms of minutes and seconds. 1. On the attached graph color portions of the line for each season (Winter: Dec 20-Mar 20; Spring: Mar 20-June 20; Summer: June 20-Sept 20; Fall: Sep 20-Dec 20). Make a key for each season. 2. What was the apparent size of the Sun on Feb 10? What was the apparent size of the Sun on Apr 20? 3. In general when an object is near to you it appears to you to be (larger/smaller) than when it is farther away, even though its true size has not changed. 4. Based on the attached graph the Sun appears to be largest during the (winter, spring, summer, fall). Since it appears to be largest, it should be (closest to/farthest from) Earth at this time.

4 5. Based on the attached graph the Sun appears to be smallest during the (winter, spring, summer, fall). Since it appears to be smallest, it should be (closest to/farthest from) Earth at this time. 6. According to your graph on which day(s) would Earth be closest to the Sun? This is called (aphelion/perihelion) 7. According to your graph on which day(s) would Earth be farthest from the Sun? This is called (aphelion/perihelion) 8. Compare your estimated dates (from question 5 and 6) with the actual dates of aphelion and perihelion in the textbook. The actual dates are: for perihelion and for aphelion. How close were your estimates to the real dates? 9. Based on your answers in this lab, EXPLAIN how we know that our changing distance to the sun is NOT a cause of seasons. Refer to your previous answers to help.

5

6