The following activities will prepare your students for a lesson on longitude and time and provide them with a strong sense of the historical events surrounding John Harrison's search for longitude.
Step 1: Establishing the Base Concepts of Time
The two most important motions of the Earth give us the two most important units of time.
Ask students, "What are these two motions that the Earth makes, and what are the end results of these two motions?" (The Earth rotates or turns on its axis once in every twenty-four hours. This rotation gives us day and night. The other important motion is the Earth's revolution around the sun. This takes 365 1/4 days and gives us the seasons.)
Ask students, "What is a leap year?" (If we take four 1/4 days, we get a whole day, which we add on at the end of February every four years. We call that year a leap year.)
Present this information visually (by means of a bulletin board).
||365 1/4 days
||365 1/4 days
||365 1/4 days
||365 1/4 days = 366 days (a leap year)
|Four 1/4 days = 1 whole day
Ask students, "At what hour does our new day begin?" (Most students will say midnight. Actually, a new day begins 1 second after midnight. Astronomers, however, use midnight so that the average or mean solar day can be divided into 24 equal parts. This allows the clock's hour hand to move around twice in a 24-hour period. From one midnight to the next midnight is one solar day.)
Tell students that they will be visiting a Web site to investigate the causes of seasons and the formation of day and night. Have students log on to the Web site at www.geo.utep.edu/class_notes/3103_julian/seasons.html
Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to examine the Web site and determine 1) What are the reasons for the seasons?, and 2) How are day and night formed? (Seasons are caused by the uneven heating of the Earth's surface by the sun as the Earth revolves around it. Day and night are caused by the Earth's rotation on its axis.)
Once the students have completed a brief oral explanation of the causes of seasons and gained some insights into the causes of day and night, divide the class into two groups, A and B.
Tell Group A that they are going to visit a Web site in order to examine day and night around the world. Have Group A students log on to the Web site at http://www.worldtime.com/cgi-bin/wt.cgi?cnt = 127621&ID=c914526da5 . Provide a FOCUS FOR MEDIA INTERACTION, asking the students in Group A to determine what the Circle of Illumination is. (The Circle of Illumination determines where day ends and night begins.)
At this time, have your students insert global coordinates for a region. Then have them predict, based on the coordinates, whether that region would experience daylight or nighttime. It is advisable that the teacher allow students to practice with this site in order to have them fully understand how the Earth's rotation creates day and night around the world.
While Group A is working on the computer simulation, give Group B their FOCUS FOR MEDIA INTERACTION, asking them to determine how difficult it is to get planets orbiting around the sun. Ask students to log on to the Web site at www.explorescience.com/activities/activity_list.cfm? Category ID = 7. Ask students, "Since we know that midnight begins a new day, what is the most important hour of the day?" (The most important hour of the day for astronomers is not midnight but midday, when the sun is at its highest point in the sky -- its zenith -- or meridian.)
Step 3: Establishing a Rationale for A.M. and P.M. (See Fact Sheet)
Students will be looking at a teacher-made bulletin board (see attached sample for ideas) to visualize and understand the path of the sun and what occurs when the sun reaches its zenith at exactly noon. Students will learn that the most important meridian passes through the Observatory at Greenwich, England, and it is called the prime meridian. The prime meridian's location is 00 longitude, and the word "meridian" means midday or noon. When the sun reaches its zenith and crosses the meridian, for all places along this meridian it is exactly 12 o'clock noon. Ask students, "What is the time before or after the Zenith meridian?" (The bulletin board shows the words Ante Meridian, which means Before Noon and Post Meridian, which means After Noon.) Ask the students, "What happens when we take the first letter from the words "Ante Meridian" and "Post Meridian"? (We get A.M. and P.M.)
Explain to your students that you will now be examining the historical event that created the search for longitude, beginning in the year 1714. You will be exploring this event through the use of a video, then through the use of a Web site.
Insert Nova, "Lost At Sea: The Search for Longitude," into your VCR.
Provide your students with a FOCUS FOR MEDIA INTERACTION by asking them to determine 1) how navigators of the early 17th century knew how fast their ships were traveling, 2) why we measure the speed of ships in knots, and 3) what the term "dead reckoning" means. Ask your students to raise their hands as soon as they feel that they can answer those questions. START the video when the screen is filled with a sailor hauling a ship's line. Other sailors can soon be seen working on board a "tall ship." The narrator states, "Consider the problems of the sailors and navigators of the 1700s." PLAY the video until you hear the narrator say, "But it was then the only way to estimate distance." PAUSE the video.
CHECK for comprehension, and ask your students the following questions about how navigators knew how fast their ships were traveling:
"What was the contribution of this knowledge to the use of log and line?" (The log was a triangular piece of wood, onto which was tied the line, a knotted line, with knots tied at intervals of about 48 feet, 3 inches.)
"How was this instrument used at sea to measure the speed at which the ship was sailing?" (The navigator would throw the line over the side of the ship. The first 50 feet of line would be clear, but as soon as the marker (knot) on the line passed through the navigator's fingers, he would shout "turn" and count the number of knots that slipped through his fingers in the time it would take a 28-second sand glass to flow through. This would give the speed of the ships in knots. Measuring the speed of the ship in knots was one of the techniques of dead reckoning.)
"Were there any advantages or disadvantages to using the method of "dead reckoning" at sea? (It was a crude method, and did not allow for currents or crosswinds, which could easily push a ship off course. But at the time, it was the only way to estimate distance traveled at sea.)
One major aspect of checking your students' understanding of information is to institute what is known as an Embedded Assessment. Let us do that at this point in our lesson. Provide your students with a FOCUS FOR MEDIA INTERACTION by telling them that they will be visiting a Web site that will show the log and line viewed in the previous video segment. Volunteer students will be asked to identify each picture and give oral descriptions of the use of logs and lines on board the early sailing vessels. This activity will allow for student-to-student interaction when the teacher asks students to verify each other's descriptions of the use and functions of the log and line. Have students log on to the Web site at http://people.ne.mediaone.net/saville/chiplog.htm
Step 2: Establishing the Purpose and Understanding of Gridlines
Provide your students with a FOCUS FOR MEDIA INTERACTION, asking them to focus on the importance of grid lines on globes and how navigators of the early 1700s used at least one of these lines.
Step 3. Establishing an Understanding of the Value of Lines of Latitude and Longitude
PLAY the video from the Pause Point. A spinning globe fills the screen, and the narrator says, "For centuries mapmakers have used grid lines to indicate points on the surface of the Earth." STOP the video when you hear the narrator say, "But without any means of figuring longitude, their east-west position, latitude was all navigators could hope to use."
Ask your students the following questions:
"How are lines of latitude recognizable on globes?" (Lines of latitude are represented by parallel horizontal lines circling the earth.)
"What is the major line of latitude, and what is its address?" (The Equator is the major line of latitude. Its address is 00 latitude.)
"How is longitude depicted on globes?" (Longitude is depicted by vertical lines or meridians running from pole to pole.)
"What instrument did navigators have for measuring latitude, and what were the impediments to using this instrument at sea?" (The crook staff was used, and since it was held up to the eye, you could sustain damage to the bone or orbit of the eye, or you could go blind staring into the sun.)
NORTH/SOUTH LINES = MERIDIANS OF LONGITUDE
Provide a FOCUS FOR MEDIA INTERACTION by telling students that they are going to practice locating cities across the world via a Web site. Ask your students to log on to Look-Up Latitude and Longitude: The Astrodienst Atlas, at www.bcca.org/misc/qiblih/latlong.html
Tell the students that some of them will be given a major city and asked to enter the name of that city into the site, then record on their Data Sheet the latitude and longitude of each given city. While some of the students are engaged in the Internet activity, the other students can be manually checking the cities' locations using their atlases in order to check the accuracy of the computer-driven location.
|New York, U.S.A.
|Mexico City, Mexico
Ask the students, "What do you notice about the given locations in terms of latitude and longitude?" (Students should notice that latitude is given in degrees north or south, and that longitude is given in degrees east or west.)
Step 4: Establishing the Idea for Discovering Longitude through Clock Building
Provide a FOCUS FOR MEDIA INTERACTION by asking your students to determine what John Harrison's major discovery about pendulums was. PLAY the video as John Harrison can be seen at work in his clock shop. He is experimenting with a pendulum. The narrator states, "For John Harrison, even at the age of twenty, clockmaking had become a passion." STOP the video when John Harrison states, "I judge that my intended sea clock will indeed require the regularity, the performance that has not been seen before the nicety of 2 or 3 seconds a month."
Do not CHECK for comprehension yet.
Step 5: Establishing the Concept that Temperature Affects Metals
Provide your students with a new FOCUS FOR MEDIA INTERACTION, asking your students to determine if temperature affects the accuracy of pendulum clocks. FAST FORWARD the video until you see John Harrison sitting in his living room and the narrator says, "John Harrison's living room had become a genuine scientific laboratory." PLAY the video. When the narrator states, "By 1730, John Harrison had collected enough information on the effects of temperature, friction, and gravity to convince himself that he could really build a sea clock accurate and reliable enough to win the Longitude Prize," STOP the video.
Ask students, "What was one major problem that John Harrison had to overcome to assure the accuracy of his pendulum clocks?" (The pendulum must always stay at the same length without altering based on factors of heat and cold.)
"What did he do in order to ensure that his pendulums stayed at equal lengths at all times?" (He made his pendulums by combining wires of the metals brass and iron.)
The earth rotates once every 24 hours. Ask your students, "Since the Earth is a sphere, how many degrees are there in a sphere?" (There are 360° in a sphere. The prime meridian and the Equator form perpendicular lines. At the intersection of perpendicular lines, right angles (90°) are formed. Since there are four 90° angles formed, 90° times 4 produces 360°.)
Since the Earth turns 360° in one day (24 hours), how many degrees does the earth turn in one hour? (Divide 360° by 24 hours = 15° an hour.)
Let us assume that the time at Greenwich, England, is noon, and that you are standing in a city 15° east of Greenwich. What time would it be in that city? (Since we know that every 15° is equivalent to 1 hour of time, and the Earth turns from west to east, the time in that city has to be 1 hour later than in Greenwich. Therefore, the time would be 1:00 p.m.)
Let us assume that you are now in a city 30° west of Greenwich, england. Ask your students what time it would be in that city. (Again, since the city is 30° away, it means that the city is 2 hours away. Since it is west of Greenwich, and the Earth turns from west to east, the time in that city has to be two hours earlier. Therfore, the time in that city would be 10:00 A.M.)
Let us assume that the time at City A on the 50° E. line of longitude is midnight. Ask your students, "What would the time be at City B located on the 40° west line of longitude?"
Let your students draw a diagram that should look like this:
40°West Line of Longitude 0° Prime Meridian 50° East Line of Longitude
| | |
| | |
| | |
City B Time=? City A Time=Midnight
(a) From the prime meridian to City A, the distance in degrees is 50°.
(b) From the prime meridian to City B, the distance in degrees is 40°.
(c) Therefore, the total distance from City A to City B in degrees is 90° (50° plus 40°).
(d) Convert degrees apart into time apart.
(e) Every 15° is equivalent to 1 hour. Therefore in 90° there are 6 hours. (90° divided by 15° = 6 hours.)
(f) City B is west of City A. Therefore it must be earlier than City A (six hours earlier than midnight), which puts the time in City B at 6 P.M.
Have your students try this problem with a "little twist" to it. Ask your students, "If the time at City A, located on the 90° west line of longitude, is 5 P.M., what would the time be at City B located on the 80° east line of longitude? (3:40 A.M. the next day. Since the cities are on opposite sides of the prime meridian, you add degrees apart for a total of 160°. Convert this into time apart, 160° divided by 15° to the hour. This gives you 10 hours with 10° left over. Convert 10° left over into a fraction, 10°/15°, and multiply by 60 minutes to 1 hour, giving 40 minutes or 10/15 of an hour = 2/3 of an hour or 40 minutes. Since city B is east of City A, it must be a later hour -- 10 hours 40 minutes later than City A. This puts the time at 3:40 A.M.)
Ask your students if they see any connection between this activity and John Harrison's search for longitude. Did this activity give you insight into how students could calculate the longitude of a given place if you know the time between two cities?
This lesson lends itself to students using and understanding Map Scale. Students could also learn to convert statute miles to nautical miles.
SOCIAL STUDIES/CULTURAL IMPLICATIONS
A Revolution in Timekeeping
On this site, students can trace the development of timekeeping instruments throughout history.
Students can obtain a world map that has degrees of latitude and longitude on it. Using poker chips or by drawing on the map, students can play the game Battleship to strengthen their understanding of location using lines of latitude and longitude.
Teachers may also set up a grid board, which allows students to play TIC TAC TOE, 3/4 in a line, using the world coordinate system of Latitude and Longitude.
Students can create an "Around the World in 80 Days" game, allowing players to research and chart the shortest course around the world. For example, one group of students could travel around Cape Horn while another group uses the Panama Canal to get to California. Who travels the shorter distance, and by how many nautical miles?
Teachers may conduct activities that demonstrate the effect of temperature (heat) on solids, liquids, and gases.
Students may conduct investigations as to the effect of heat and cold on metals, using metals such as brass, iron, and copper. Using a tool called a conductor bar, which has prongs made up of many different metals radiating from a central point, students can place beeswax on the tip of each prong, hold the central point over a heat source, and observe which prong loses its beeswax first.
How Pendulum Clocks Work
On this site, students can conduct investigations into the working of clock pendulums, using the variables of weight and length of pendulums to determine their effects on clock time.
Students could research how various animals (locusts, homing pigeons, salmon, etc.) "find their way home" during seasonal changes or spawning.
Have an "Invention Convention" in which students build sundials, sand clocks, or water drip clocks and conduct investigations in order to compare their inventions against standard time clocks.
- Invite an airline professional or a Coast Guard representative to your classroom to discuss how longitude and latitude are used in navigation.
- Invite a health care professional to your classroom to discuss why travelers experience jet lag, and what can be done to combat it.
- Visit the stock exchange and investigate the impact of time zones on investment trading.
- Visit a clock repair shop to investigate the mechanics and upkeep of time pieces.
- Contact the International Cartographic Association, and interview members to determine how maps are made.