ASTRONOMY LESSON PLAN
Title of lesson: Building A Telescope
Date of lesson: March 21, 2004
Length of lesson: 3 hours
Description of the class:
Name: Algebra II
Grade level: High School
Honors or regular: Both
Source of the lesson: ÒBuilding Your Own Telescope Made EasyÓ by Claire Hodgin and Betty Stennett
The Lesson:
I.
Overview
Students will have three main projects to accomplish during this lesson.
(1) Students will find the focal point of their telescopes, have the eyepiece hole cut, and line the secondary mirror up correctly.
(2) Students will find the center of the spider and have the legs cut before gluing it into the telescope.
(3) Students will calibrate the large mirror in the base of the telescope.
II.
Performance or learner outcomes
Students will learn about the focal point of a concave mirror using a laser reflected from a small mirror. The students will be able to: find the center of an object, measure the focal point of their telescope, and determine where the eyepiece hole should be located.
III. Resources, materials and supplies needed
Spoon, laser pointer, small concave mirror, erasers with chalk dust, spider, ruler, pen, telescope, large mirror, flashlight, board, markers, eyepiece mount, eyepiece, cardboard, screws, saw, drill, wrench
Five-E Organization
Teacher Does Student Does
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Pre-Engage: The teacher will explain that this morning students will be building a telescope that will be used in the afternoon. The teacher will emphasize the importance of working efficiently due to the limited amount of time given. Also, the teacher will explain that the purpose of this project is to show how math is applied in the real world. For this reason no new math will be learned, so it is important for students to apply their current math knowledge during this project. Since our time is very limited, the teacher will tell the students that it is vital they ask questions when unsure of what to do. In addition, the teacher will also emphasize the importance of being careful with the telescopes. Large expensive mirrors will be placed into the telescopes, so it is important to be extremely cautious when lifting or moving the telescopes. Also, the teacher will make it clear that students are not to cut anything until a teacher has checked it first and never to glue anything unless they have double checked it. The teacher will then ask for questions and answer any students bring up. Questions
Engage: Learning Experience: The teacher will ask the students what they know about telescopes. The teacher will ask students what pieces are essential to a telescope. The teacher will bring out a small concave mirror and pass it around asking students to hold it by the edges being careful not to touch the mirror. After all students have personally viewed the mirror, the teacher will ask the students what interesting things they noticed about the mirror. The students will notice the mirror is concave. The teacher will ask the students if they know any other concave objects. The teacher will show the students a spoon. The teacher will ask which side of the spoon is concave and which side is convex. The teacher will ask the students how the curving of the mirror affects reflections. The teacher will tell the students that a concave mirror reflects a ray of light in a unique way. The teacher will ask one student to stand in front of the students and hold the mirror towards the students being careful to hold it very steady. The teacher will select another student to stand over the mirror and hit two erasers together forming a cloud of chalk dust. The teacher will turn down the lights and stand behind the sitting students, pointing a laser pointer at the mirror. The teacher will move the laser in a circular motion around the outside edge of the mirror and will ask the students to observe the reflection of the laser. The teacher will allow the students to move in order to view the laser light from the side. The teacher will call on students to tell what they observed. The teacher will point the laser at the left side of the mirror and ask the students where the reflection angles. Then the teacher will point the laser at the right side of the mirror and ask the students where the reflection angles. The teacher will continue shining the laser at different places on the edge of the mirror until the studentÕs notice that the reflection of the laser always tilts towards the center of the mirror and all reflections converge at a point. The teacher will use the board to draw the reflections converging at one point. The teacher will explain that this point is called the focal point and is the point where objects reflected off a concave mirror are most clear. Also, the teacher will point out that the distance from the mirror to the focal point is the focal length. The teacher will ask the students to think about how this might help them when they build the telescopes. Questions
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What the students are doing: Listening attentively. Asking questions. Expected
Student Answers 1. Ask an adult to check it. 2. Double check it. Explain what they know about telescopes. Listing pieces that are essential to a telescope. Observe the mirrors and pass them around quietly. Answer questions and make observations. One student will hold the mirror while another makes dust with chalk erasers. Make observations and answer questions. Expected
Student Answers 1. They are used to see far away objects. 2. Tube, mirrors, eyepiece. 3. It is curved inward. 4. Concave. 5. Spoon, coconut, flashlight. 6. The side curved inward is concave, the side poking outward is convex. 7. They are distorted or stretched. 3. It reflects toward the center of the mirror. 4. So it will focus a far away object at a close focal point. |
Evaluate
Teacher Does Student Does
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Explore: Learning Experience(s) The teacher will ask the students to pretend that the light from the laser is the light given off by the moon. The teacher then asks the students to pretend that a telescope is put in front of the student holding the mirror. This makes it impossible for the students to see the focal point from the sides of the telescope. The teacher asks the students how they will be able to see the reflection. The teacher will point out that if a student steps in front of the laser to see the focal point inside the tube, they will block out the laser light. The teacher will then ask the students how they can solve this problem. The students will discover that the light can be reflected off another mirror. The teacher will point out that a second mirror will simply reflect an image back at the original mirror. The teacher will ask the students what can be done to fix this problem. The students will discover that the mirror needs to be tilted, so the image reflects toward the inside of the telescope. The teacher will show students the spider with the secondary mirror attached to the base that will be given to them, but announce that there is a problem: the legs of the spider are too long for the tube. The teacher will explain that it is up to the students to find a way to center the spider and mark where the legs should be cut. The teacher will point out that it is better to make the legs too long than too short. In addition, the teacher will tell the students the telescope will be approximately 8 inches in diameter and the spiders have three legs equally spaced around the center hole. The tubes are not exact and some are slightly more oval than others, therefore it is important to visually make sure the spider is centered in the tube. The teacher will give students the spider and the tube and will allow time for students to figure out that each leg of the spider is a radii and should be 4 inches in length. After the students have marked the three legs, the teacher will ask Hank to cut the spider leaving a little extra on each leg so the spider is not too short. The teacher will then ask a student to sand down the legs until the spider can be put into the tube. Questions
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What the students are doing The students are listening attentively and asking questions by raising their hands. Listening and answering questions. Discussing and asking questions. Expected
Student Answers 1. Look down the tube. 2. The student will block the laser light. 3. Divert or reflect the light. 4. Another mirror. 5. They are radii. |
Evaluate
Teacher Does Student Does
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Explain: Learning Experience(s) The teacher will show students the large mirror that will be placed in the base of the telescope. The teacher will emphasize the importance of never touching the mirror. The teacher will select a student to hold the mirror in front of the students. The teacher will ask where the students think the focal point on a large mirror will be. The teacher will ask the students if the focal point will be closer or farther away than the focal point to the small concave mirror seen earlier. The teacher will tell the students that chalk dust cannot be used around the large mirrors because they are too expensive, so in order to find the focal length the students will use a flashlight. The teacher will ask for three students to volunteer. One will hold a flashlight, one will hold the large mirror, and the other will hold a board directly next to the flashlight. The student holding the flashlight will point it directly at the mirror and the reflection of the light will shine onto the board. The flashlight will have a paper arrow taped to the front, so it can be seen whether the arrow is clear or fuzzy. The teacher will ask the students to observe the reflection as the student moves the flashlight toward and from the mirror. The teacher will explain that the distance from the mirror to the point where the reflection is most clear is the radius of the circle created by the mirror. The focal length is half of the radius. The teacher will ask the students to decide where the arrow is most clear as a group. Once the students have decided the focal length, the teacher will introduce a problem: We now know the focal length is 1 meter, but our tube is 1 meter long, so we cannot put the spider at the very edge of the tube. How are we going to move the reflection back inside the tube? Since a secondary mirror is used to reflect our image to a hole in the telescope, we need to decide where this hole should be placed. The teacher will ask the students to discuss what they know and how they can piece these things together to solve the problem. The teacher will draw a picture of the tube with the primary and secondary mirrors and the eyepiece hole. The teacher should ask the students what the length from the primary mirror to the secondary mirror is and what the length from the secondary mirror to the hole in the tube is. The teacher should guide the students to figure out where the hole for the eyepiece should be placed. Since the focal length is 1 meter and the radius is 4 inches, the spider should be placed 4 inches down from the front of the tube. In addition, the eyepiece hole should be cut 4 inches down from the front of the tube in order to look directly at the secondary mirror. The teacher will ask the students to mark exactly where the eyepiece hole should be cut. The teacher will double check the students work by measuring the center of the eyepiece hole to be 4 inches from the top of the tube. The teacher will then ask Hank to cut the hole and screw in the eyepiece mount. The teacher will explain that once the mount for the eyepiece has been screwed in, the spider will need to be lined up correctly inside the tube. In order to line it up, we will need to know where the center of the large mirror is. The teacher will give the students paper, a pencil, and a reinforcement sticker and ask them to use these tools to find the center of the mirror. The teacher will allow the students to work together as a group and then will show the students how to put the large mirror into the telescope. The teacher will then ask the students to insert the spider into the tube and center it by looking through the eyepiece and moving it around until the reinforcement is in the center of the secondary mirror. Since only one student at a time can look through the eyepiece, the teacher needs to make sure that all students have a chance to see. After the spider is centered, the teacher will explain that the telescope must now be calibrated. This means that the primary mirror needs to be positioned at the correct angle. Since your eye is reflected onto the primary mirror by the secondary mirror, we will use this to calibrate the primary mirror. The teacher will explain that as the screws on the base of the telescope are screwed in, they will push against the mirror causing it to tilt, which will cause the reflection to move. The teacher will explain that the goal is to get the reflection of your eye centered onto the reinforcement. The teacher will select one student to look through the eyepiece while another turns the screws at the base of the telescope. The teacher will call on different pairs of students to do the calibration, so everyone will get an opportunity to participate in the calibration. Once the telescope has been calibrated the teacher will give the students the eyepiece. Since the eyepiece is too small for the hole, the teacher will explain that cardboard should be wrapped around the eyepiece to keep it from slipping in or out of the telescope. The teacher will give the cardboard to one student and the eyepiece to another and ask them to work together to make the eyepiece fit. Finally, the teacher will explain that the spider will need to be glued into the tube before going to lunch. The teacher will tell the students that once glue has been put into the telescope, it should not be tilted because we do not want glue to drip onto our primary or secondary mirrors.
Questions
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What the students are doing Listening.
Watching as a student volunteer holds the mirror.. Answering questions. Volunteering to hold the flashlight, mirror, and board. Watching as student volunteer shines the flashlight on the mirror creating a reflection. Deciding on the clarity of the arrow. The students will recall a secondary mirror is used to reflect our image to a hole in the telescope. Discussing information and solving the problem. Answering questions. Marking the eyepiece hole. Working together to find the center of the mirror. The students will trace the mirror and cut it out. They will then fold the paper twice to find the center. The students will cut a small hole in the center of the paper and lay it over the large mirror. The students will then put a reinforcement on the mirror where the small hole has been cut in order to mark the center of the large mirror. Calibrating the telescope. Making the eyepiece the correct size to fit in the telescope. Expected
Student Answers
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Evaluate
Teacher Does Student Does
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Extend
/ Elaborate: Learning Experience(s) If time allows, the teacher will show the students the stand for the telescope. The teacher will show the students how the base works and will explain that two cradles need to be attached in order to hold the telescope on the stand. The teacher will explain that the telescope will need to have enough room to go horizontally and vertically. The teacher will show the students a picture of how the cradle boards attach to the stand. In addition, the teacher will tell the students that the cradle boards should be at least 1 inch from the bottom of the stand to give it enough clearance room to move. The teacher will ask the students to hold the cradle boards in position as Hank screws them in. Questions 1. What are the cradle boards used for? 2. How far should they be from the bottom of the stand? Why? |
What the students are doing Listening and watching.
Holding cradle boards in position.
Expected
Student Answers
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Evaluate