Chapter 6: Light and Telescopes

a. What is meant by electromagnetic radiation? What are some of the properties of light?

b. What is meant by the wavelength and frequency of light?

c. What is an Angstrom? I use Angstroms in class not nanometers. What is the velocity of light?

d. What is a photon? What is meant by the wave-particle duality of light?

e. What is the relationship between wavelength, frequency, and energy of light? How does the energy of a photon of light depend on its wavelength? What kind of light is most energetic, least energetic?

f. What are the various parts of the spectrum? Note the definitions of infra-red, ultraviolet, X-ray, Gamma-ray, ..Know the different kinds of light (page 103 Figure 6.2).

g. What is meant by atmospheric windows? Where in the spectrum is the atmosphere transparent, opaque?

h. What are refracting telescopes? Reflection telescopes? How do they differ?

i. What is the objective? Eyepiece?

j. What is the fundamental difficulty with refracting telescopes? (Chromatic Aberration)

k. How does a telescope form an image? Note that the image is upside down. How is the Eye like a telescope? What is the focus of a lens or mirror? What is the focal length of a lens or mirror?

l. What is an achromatic lens? Does it really fix chromatic aberration?

m. What is the objective mirror? What is a newtonian telescope? Cassegrain telescope? Prime Focus? (Look at Figure 6-6)

n. Skip mountings.

o. Where are the Keck telescopes located? Why on a mountain top?

p. What is the light-gathering power of a telescope? On what does it depend?

q. What is the resolving power of a telescope? On what does it depend? Why is it relatively unimportant for ground based telescopes? What atmospheric effect reduces the resolving power of a telescope? What are some of the advantages of a reflector over a refractor for large astronomical telescopes.

s. Active optics means that the shape of the mirror can be changed (slightly) over a few minutes to correct for the atmosphere.

t. What are some of the new large telescopes called? LBT, VLT, ... I showed pictures and discussed them in class.

u. Why are radio telescopes so big? A radio interferometer makes a lot of separate radio antennas act as a single antenna improving the resolution. One such observatory is the VLA. Where is it located? Did you see it in the movie “Contact”? We do not listen to the signal from a radio telescope.

v. Where is the Arecibo radio telescope located?

w. We launch satellite observatories to observe in wavelengths blocked by the atmosphere or to observe without worrying about the effects of “seeing.”

x. Some of the infra-red satellites were ISO, IRAS, and Spitzer. In the UV we had IUE, EUVE, and HST. In the X-ray we have CHANDRA.