Solutions for Assignment #6 (Chapter 6)

Read Chapter 6, Section 2 and the part of Section 4 that covers observations outside the visible part of the spectrum

1.) What is the function of a lens or a curved mirror in a telescope?
Answer: Both change the angle of the incoming light rays (example, the lens bends the light rays) so that the rays of light will focus.

2.) How are telescope observations better than "naked eye" observations?
a.) telescopes can collect more light than a human eye can
b.) telescopes can have better angular resolution than a human eye
c.) both of the above
d.) none of the above

3.)
a.) In order to see the features on a planet clearly, do you want your telescope's diffraction limit to be smaller than the angular separation between the features on the planet, or do you want your telescope's diffraction limit to be larger than the angular separation between features on the planet
Answer: You want the telescope's diffraction limit to be smaller than the angular separation between the features on the planet.
b.) Explain why
Answer: The diffraction limit is the smallest angular separation that you can see with your telescope. If the features on the planet are spaced at even smaller angles than the diffraction limit, then your telescope will blur their light together and you won't be able to see the features clearly.

4.) Compare a 5 meter telescope with a 10 meter telescope:
a.) Which has the better diffraction limit and by what factor is it better than the diffraction limit
of the other telescope? (The wavelength of the light to be observed is 656 nm, but it is possible for
you to do this problem without knowing the wavelength.)
b.) Which has the larger light collecting area and by what factor?
Answer: The 10 meter telescope has a better diffraction limit. It is half as large as that of the 5 meter telescope.
b.) Which has the better light collecting area and by what factor?
Answer: The 10 meter telescope has 4 times as much light collecting area as the 5 meter telescope.
ever-changing 2. Each 2 of area. So, in order
2 = i.e. 4 x 108.

5.) If our eyes don't see radio frequency light, how do astronomers make images of radio emission? Answer: The detectors can detect the brightness of objects in radio-frequency light. They can also detect the shape of the object. This information is stored. So that humans can work with the information, the stored information is translated into a visible-wavelength image. This can be done by color-coding visible colors to radio wavelengths (that makes a "false color" image).

6.) Which one of the following would be an example of a spectroscopic observation?
a.) Astrid, the astronomer wanted to study a particular optically thin gas cloud. Unlike the relatively bright Orion Nebula, her cloud was very dim. So, Astrid studied it by recording the light from a star located beyond the gas cloud and measuring how much 410nm, 434nm, 486nm, and 656nm light the gas cloud had absorbed.
b.) Astrid, the astronomer wanted to study a particular binary star system. Her binary star system was very far away and so she was not able to resolve the two stars in her photographs. So, Astrid studied it by recording the system's flux every minute over several weeks. She could see that the flux varied in a regular, periodic fashion.
c.) Astrid, the astronomer wanted to study the bubbles made by exploding stars. Since her favorite bubble was so faint, she had to put a filter on her telescope. She used a filter that only allowed 656 nm light to come through to the detector. From her observations, she was able to see the circular shape of the bubble.
d.) None of the above
Answer: a. In option a, Astrid is measuring and analyzing aspects of the spectrum (the emission lines) from the gas cloud. She is using that information to learn about the cloud. Option b is not right because it is a timing observation. Option c is really an imaging observation. The use of the filter to select a single color of light is really being done in order to make a better image, not to learn about the spectrum. In order to have a spectrum, you must have more than one color of light. But, Astrid has thrown away all the other colors of light in option c.