MAKING A SIMPLE SEXTANT TO FIND LATITUDE by Diane Vardner Will Rogers Intermediate School Lawndale, CA 90260 THEMES: Stability , Scale and Structure GRADE LEVEL: 5- 10 GROUP SIZE: 2 students per group SETTING: Classroom, outside, or auditorium APPROXIMATE TIME REQUIRED: 1 class period plus 1 homework assignment MAJOR CONCEPTS 1. Most stars change their positions as Earth rotates and revolves. 2. The axis of Earth is inclined with respect to the poles and remains constant. 3. The North Star can be used to determine geographic north. 4. The numbers specifying location on Earth are known as latitude and longitude. 5. The angle at which the North Star can be observed relative to the horizon differs in each part of the world. At the equator, the angle is O degrees. At the North Pole, Polaris is observed at 90 degrees. In the northern hemisphere, latitude is the same as the angle which the North Star is observed above the horizon. SCIENCE PROCESSES Observing, Interpreting Data, Using Numbers, Measuring VOCABULARY 1. Polaris: The North Star, the best known and brightest star in Ursa Minor (the Little Dipper). 2. Latitude Lines: Imaginary lines that run parallel to the equator, used to find location on Earth relative to north and south. 3. Horizon: The line where the sky appears to meet Earth. MATERIALS NEEDED Per student: protractor, tape, jumbo paper clip, scissors, 20 cm string, metric ruler, clear plastic straw GENERAL PROCEDURES See attached worksheet. GENERAL INFORMATION FOR TEACHERS 1. The determination of latitude is based on the formula (latitude of any place in the northern hemisphere) = (latitude of the North Star at same place). 2. When working inside, use a large room like the gym or auditorium and locate items near the ceiling at the opposite end of the room. 3. When working outside, locate tall buildings, poles, trees, etc. 4. This activity goes well with studying explorers in history and angles in math. REFERENCES Degani, Meir H., Astronomy Made Simple WORKSHEET HOW CAN YOU FIND LATITUDE USING THE NORTH STAR? MAKING A SEXTANT. Name: Date: Per.: MATERIALS: Protractor, jumbo paper clip, 20 cm string, clear plastic straw, tape, scissors, metric ruler. PROCEDURE: 1. Tape the straw to the protractor so that the straw goes through the 90 degree and center mark (or center hole). 2. Tie the string to the paper clip. Making sure that the string hangs freely, tape it to the center mark. (Note: the string should go through the O degree mark if the straw is held parallel to the ground.) 3. Pick an object high on the ceiling or outdoors above ground. Sight this object through the straw. Press the string against the protractor when it stops swinging and read the scale on the protractor. (Read the scale that ranges between O to 90 degrees.) This is the angle of the object above ground. 4. Take two more readings of this object and average the results. (Make sure you are at the same location!) 5. Pick 1 more object and take three readings, averaging your findings. 6. Go outside on a clear night. Use a compass to locate north. Find the Big Dipper. Use the pointer stars to locate the Little Dipper and the North Star. 7. Find the angle of Polaris above the horizon. Repeat step 4 and find the average for Polaris. Find the latitude of your City on a map. How do the two numbers compare? OBJECT #1 READINGS 1st 2nd 3rd AVERAGE (sum / 3) OBJECT #2 READINGS 1st 2nd 3rd AVERAGE (sum / 3) Polaris FOLLOW-UP QUESTIONS 1. What are some disadvantages to using a sextant? 2. How could knowing your latitude help you? (Imagine you are an explorer.) 3. At the equator, where would you look to find Polaris? 4. At the North Pole, where would you look to find Polaris? 5. What is the latitude of the equator? The North Pole? ********************************* This material was taken in whole, or adapted, from, "THE CATALYST COLLECTION: OUTSTANDING EARTH / SPACE SCIENCE ACTIVITIES" Edited by Gaylen R. Carlson, Ph. D., California State University, Fullerton, Department of Geological Sciences, Fullerton, CA 92634-9480, (714) 773-3882. *********************************