MasteringAstronomy Chapter 6

How much greater is the light-collecting area of one of the 10-meter Keck telescopes than that of the 5-meter Hale telescope? a. 2 b. 4 c. 8 d. 16

b. 4

Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have? a. High turbulence b. High spectral resolution c. High angular resolution d. A radio telescope

b. High spectral resolution We learn chemical composition by studying spectral lines, so higher spectral resolution makes it easier to learn chemical composition.

Choose the correct statement describing, what will you see if you look at them with a telescope that has an angular resolution of 0.5 arcsecond. a. Two distinct stars. b. One point of light that is the blurred image of both stars. c. Nothing at all.

b. One point of light that is the blurred image of both stars.

Interferometry uses two or more telescopes to achieve: a. a light-collecting area equivalent to that of a much larger telescope. b. an angular resolution equivalent to that of a much larger telescope. c. both the light-collecting area and angular resolution of a much larger telescope.

b. an angular resolution equivalent to that of a much larger telescope.

How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope? a. two times b. four times c. six times

b. four times

The two factors that determine how well a telescope with a particular camera can detect dim galaxies are __________.

light-collecting area and exposure time with the camera

The two factors that determine how well a telescope with a particular camera can detect dim objects are __________.

light-collecting area and exposure time with the camera

Telescope X has a single 1-meter mirror, and Telescope Y has two 1-meter mirrors that work together. Telescope Y therefore has ______ the light-collecting area of Telescope X.

twice

The light-collecting area of an 8-meter telescope mirror is _____ that of the light-collecting area of a 2-meter telescope.

16 times

Suppose astronomers built a 130-meter telescope. How much greater would its light-collecting area be than that of the 10-meter Keck telescope? Express your answer using two significant figures.

170

True or False? All forms of light easily travel through Earth's atmosphere to the ground.

False

True or False? During the day, we see most objects because of the reflected sunlight that enters our eyes.

True

True or False? If someone sees light of a particular color, then the light must be visible light.

True

Which of the following types of telescope would be useful in your backyard?

a visible-light telescope

What do astronomers mean by light pollution? a. Light pollution is light from human sources that makes it difficult to see the stars at night. b. Light pollution means contamination of light caused by chemicals in the Earth's atmosphere. c. Light pollution is a type of air pollution created by lightweight gases such as hydrogen and helium. d. Light pollution is a term used to describe the appearance of the sky in regions that are crowded with stars.

a. Light pollution is light from human sources that makes it difficult to see the stars at night. This is a major problem for many astronomical observatories, and also means the night sky is much less accessible to most humans today than it was to our ancestors.

Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope? a. adaptive optics b. grazing incidence c. interferometry

a. adaptive optics

The stars in our sky twinkle in brightness and color because of __________. a. turbulence in the Earth's atmosphere b. light pollution c. the bubbling and boiling of gases on the surfaces of stars d. rapid changes in the brightness and colors of stars caused by changes in their spectra

a. turbulence in the Earth's atmosphere Stars twinkle because turbulence keeps changing the precise amount by which light bends as it passes through the atmosphere.

Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope? a. A refracting telescope produces refracted images, whereas a reflecting telescope produces reflected images. b. Reflecting telescopes make much clearer images than refracting telescopes of the same size. c. A refracting telescope uses a transparent glass lens to focus light, whereas a reflecting telescope uses a mirror to focus light. d. It is much easier to make a large refracting telescope than a large reflecting telescope.

c. A refracting telescope uses a transparent glass lens to focus light, whereas a reflecting telescope uses a mirror to focus light. This means that the large glass (the lens) of a refracting telescope is at the front of the telescope, while the large glass (the mirror) of a reflecting telescope is at the back of the telescope.

The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is: a. larger. b. closer to the stars. c. above Earth's atmosphere.

c. above Earth's atmosphere.

If our eyes were sensitive only to X rays, the world would appear __________. a. gray, black, and white like a medical X ray b. brighter than normal because X rays carry more energy than visible light photons c. dark because X-ray light does not reach Earth's surface d. green, yellow, and orange, because those are the colors of X rays

c. dark because X-ray light does not reach Earth's surface Because X rays from the Sun do not reach Earth's surface, eyes that were sensitive only to X rays would have nothing to see.

The twinkling of stars is caused by: a. variations in stellar brightness with time. b. light pollution. c. motion of air in our atmosphere.

c. motion of air in our atmosphere.

Which of the following forms of light can be observed with telescopes at sea level? Select all that apply. a. X rays b. ultraviolet light c. visible light d. infrared light e. radio waves

c. visible light e. radio waves Both visible light and radio waves pass almost freely through Earth's atmosphere, and therefore are easily observed with ground-based telescopes. The only other light that can be observed with ground-based telescopes is infrared, but it can be detected only at high altitudes (such as mountaintops) and even then only in selected portions of the infrared spectrum.

Reflecting telescopes gather and focus light with a __________.

curved mirror

Which of the following statements best describes the two principle advantages of telescopes over eyes? a. Telescopes collect more light and are unaffected by twinkling. b. Telescopes have much more magnification and better angular resolution. c. Telescopes can collect far more light with far greater magnification. d. Telescopes can collect far more light with far better angular resolution.

d. Telescopes can collect far more light with far better angular resolution. That is, telescopes have a larger light-collecting area than the eye and a better (smaller) angular resolution.

What does angular resolution measure? a. The brightness of an image b. The size of an image c. The number of electromagnetic waves captured by an image d. The angular size of the smallest features that the telescope can see.

d. The angular size of the smallest features that the telescope can see. Therefore, a smaller angular resolution is better.

If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope? a. on Earth's surface b. on a tall mountain c. in an airplane d. in space

d. in space While visible light can be observed from the ground, ultraviolet light can be easily observed only from space. Indeed, the capability of observing ultraviolet light is a major advantage of the Hubble Space Telescope over larger ground-based telescopes.

The James Webb Space Telescope is designed primarily to observe __________. a. light of all wavelengths b. visible light c. gamma rays d. infrared light e. X-rays

d. infrared light Its location in space allows it to observe infrared wavelengths that do not penetrate our atmosphere to the ground.

Which of the following wavelength regions can be studied with telescopes on the ground? a. all light with wavelengths longer than ultraviolet wavelengths b. all light with wavelengths shorter than infrared wavelengths c. infrared, visible, and ultraviolet light d. radio, visible, and very limited portions of the infrared and ultraviolet regions

d. radio, visible, and very limited portions of the infrared and ultraviolet regions Other parts of the electromagnetic spectrum require telescopes in space.

Professor Smith has a telescope with a light-collecting area of 2 m^2. Professor Jones has a telescope with a light-collecting area of only 1 m^2. Assume both have the same type of camera and the same observing conditions. If Professor Jones wants to use her smaller telescope to obtain an image of a distant galaxy comparable to the one that Professor Smith obtains with the larger one, she should __________.

use an exposure time twice as long