Middle Georgia State University

Course title: ASTR 1010K

Chapter 3 Homework

1)Describe reflection and refraction. How do these processes enable astronomers to build telescopes?

2. Which side of the secondary mirror in Figure 3-9 is coated with aluminum? Justify your answer.

3. Explain some of the advantages of reflecting telescopes over refracting telescopes.

4. What limits the ability of the 5-m telescope at Palomar Observatory to collect starlight?

There are several correct answers to this question.

5. Why will many of the large telescopes of the future make use of multiple mirrors?

6. Compare an optical reflecting telescope to a radio telescope. What do they have in common? How are they different?

7. Why must astronomers use satellites and Earth-orbiting observatories to study the heavens at X-ray wavelengths?

8. Why did Romer’s observations of the eclipse of Jupiter’s moons support the heliocentric, but not the geocentric, cosmology?

9. The observing cage in which an astronomer sits at the prime focus of the 5-m telescope at Palomar Observatory is about 1 m in diameter. What fraction of the incoming starlight is blocked by the cage? Hint: The area of a circle of diameter d is ?d^2/4, where ? ?3.14.
10. Show by means of a diagram why the image formed by a simple refracting telescope is

“upside down”.

11. Suppose your Newtonian reflector has a mirror with a diameter of 20 cm and a focal length of 2m. What magnification do you get with an eyepiece whose focal length is

1. 9mm,

2. 20 mm, and

3. 55 mm?