MYSTERY CLASS: HELP FOR TEACHERS For Use With March 20th Data: We're all learning, aren't we? This step of the Mystery Class project may present a challenge to your students. I hope the discussion and activities below will help them understand the concepts which make it possible for you to use today's clues to estimate the longitude of our Mystery Classes. The ANSWERS are also included at the end of this report. Please reassure your students that the clues will get easier as time goes on. It may encourage them to know that they're learning something many adults don't quite understand! The Big Picture It's helpful to start by explaining the significance of the equinox. Using a globe and flashlight, review these things with your students. During the discussion, walk the globe around the "sun" a few times to simulate the yearly cycle. 1) It takes a year for the earth to rotate around the sun. 2) The earth is tilted on its axis. Notice that the northern hemisphere is tilted AWAY from the sun during half of the year and TOWARD the sun during the other half. Put the earth in the position when it's summer in the northern hemisphere. Ask your students where the days would be the longest when the earth is in this position. Where would they be the shortest? Have them notice how the latitude lines are oriented in relation to the sun. Ask them how latitude and daylength might be related. 3) The dividing lines are the spring (vernal) equinox and fall (autumnal) equinox. As you walk the earth around the sun, stop when you're at the spring and fall equinox. Notice how the latitude lines are now oriented in relation to the sun. Point out that the "north/south" tilt of the earth doesn't matter when the earth is "sideways" to the sun as it is on the equinox. Refer to your Mystery Class graphs. Show them that all places on earth have (almost!) equal day length at the equinox. Spin the globe a few times so students can see that the amount of time the sun shines on all parts of the earth is the same during the equinox. How Time and Longitude are Related In order for sunrise to occur everyplace on earth each day, the earth must spin 360 degrees. Hold your globe so students can see it with the North Pole on top. Point out that the longitude lines add up to 360 degrees. Have students figure out how many degrees the earth turns in 24 hours You may need to give them this equation: 360 degrees divided by 24 hours = (15) degrees per hour. This also means that: 60 minutes divided by 15 degrees = ( 4 ) minutes per degree. We'll use this figure in Step #5 below. Why Greenwich Mean Time is Important You have an important clue to the location of your Mystery Classrooms this week. Each has revealed what time it was (GMT) when the sun rose. This will tell you how long it took the Earth to spin so the sun would appear (rise) at their location. Since Greenwich is at 0 degrees longitude, it's easiest to count from this point. All we need to know is the time the sun rose in Greenwich and we can estimate the longitude of each place. The worksheet below will walk you through the calculations. We have provided an explanation for each step in hopes that your students will understand the rationale. (This worksheet is also being sent in a seperate message so you can print it out for your students.) MYSTERY CLASS WORKSHEET #2 ESTIMATING LONGITUDE Here's a worksheet that will help you estimate the longitude of each Mystery Class. Just follow these steps for each Mystery location. 1) Fill in the GMT sunrise figure from the Mystery Class. This is the time it was in Greenwich, England when the sun rose at the Mystery Location. Put on Line a). a) ______ 2) Fill in 6:05 This is the time of sunrise in Greenwich, England on the spring equinox. Put on Line b). b) ______ 3) Subtract b) from a) and put answer on line c). c) _____ This is the difference in time between sunrise at Greenwich and sunrise at the Mystery Location. CAUTION!!! This is not a simple subtraction equation. Remember that hours and minutes are not in decimal form. For example: Mystery Class #7's sunrise at 5:24 am is 41 minutes earlier than 6:05. Be sure to think about your answer! Note also, if the sunrise is earlier than sunrise in Greenwich, the location is east of Greenwich. For the next step you'll need to use minutes, so this step converts hours to minutes. 4) Multiply each hour by 60, add the remaining minutes and put the answer on line d). d) _____ Now you've almost got the Mystery Class' longitude! You now know how many minutes it took for the earth to spin enough for the sun to rise at the Mystery Class. 5) Divide d) by 4 and put the answer on line e) e) ______ Since the earth spins 1 degree longitude every 4 minutes, when you divide by 4 you get the degrees longitude. Note: If the number is larger than 180 the location is more than halfway around the world from Greenwich and is in the eastern hemisphere. This means the longitude will be in degrees East. Just subtract the number on line e) from 360. **************************************************************** Here are the answers your students should get. These are ESTIMATES of longitude. Mystery Site Estimated Longitude #1 19 E #2 147 W #3 170 E (see note below) #4 106 W #5 155 W #6 38 E #7 10 E #8 95 W #9 35 E #10 No Data #11 147 E Note concerning Mystery Class #3: As described in step #5 above, since the initial answer (190) is greater than 180 degrees, the location is in the eastern hemisphere. Therefore, you must subtract 190 from 360. This gives you the 170 degrees E answer.