Lesson Two Topics

Lesson Two Overview
Optical Astronomy
Radio Astronomy
What Do We Learn From Radio Astronomy?
Tools of Optical Astronomy
Tools of Radio Astronomy
Resolution
Interferometry
Analyzing Radio Data
The Advantages of Radio Astronomy
The Disadvantages of Radio Astronomy

	Activities and Quizzes

Lesson Two : Activities and Quizzes

Activity 2: Build your own telescope

Materials:

• Large diameter (approximately 7 - 10 centimeters) bi-convex lens
• Small diameter (approximately 2 - 5 centimeters) bi-convex lens
• Modeling clay
• Meter stick
• Blank white index card (4’ x 6’)
• Table facing a window (window should be approximately same height as table top)

Procedure:

1. Place an approximately 1.5-inch ball of clay at the end of the table near the window, facing the window (parallel to it). Press it firmly onto the table. Press the edge of the large-diameter bi-convex lens into the clay so that the lens stands securely in the clay. This is the objective lens.
   
   
2. Hold the white index card behind the lens so that light from the window goes through the lens onto the card. Turn out the lights in the room. Move the card toward or away from the lens until an image from outdoors is focused on the card. Mark this position.
   
   
3. Use the meter stick to measure the distance from the center of the lens to the mark at the position of the card. Record this distance (i = image distance, f = focal length).
   
   i_{objective lens} = ___________ = f_{objective lens}
   
   
4. Remove the large diameter bi-convex lens from the clay and replace it with the small-diameter bi-convex lens. Again, the lens should stand up in the clay without being held and without wobbling. This is the eyepiece lens.
   
   
5. Hold the white index card behind the lens so that light from the window goes through the lens onto the card. If they are not still out, turn out the lights in the room. Move the card toward or away from the lens until an image from outdoors is focused on the card. Mark this position.
   
   
6. Use the meter stick to measure the distance from the center of the lens to the mark at the position of the card. Record this distance.
   
   i_{eyepiece lens} = __________ = f_{eyepiece lens}
   
   
7. Replace the small diameter bi-convex eyepiece lens with the large-diameter bi-convex objective lens. Mark the focal point of the large-diameter lens. Stand up the small-diameter lens with another ball of clay. The small lens should be behind the focal point of the large lens, in a position where its focal point is at the same mark as the large lens’s focal point. The small lens should be placed so that it is in line with the large lens and parallel to it.
   




8. To use the telescope, look through the eyepiece lens, through the objective lens, towards an object outside the window. If necessary, you can focus the telescope by moving the eyepiece lens a slight distance either closer or further away from the objective lens.