Question 1

One way to improve the angular resolution of a radio telescope is to:

Accepted Answer

A) increase the exposure time. 
B) observe at a longer wavelength. 
C) observe from high mountains where atmospheric distortion is less. 
D) make the dish size larger. 
A) increase the exposure time. 
B) observe at a longer wavelength. 
C) observe from high mountains where atmospheric distortion is less. 
D) make the dish size larger.

Question 2

The prime focus cage of a telescope whose primary mirror is 3 m in diameter has a diameter of 0.5 m. What fraction of the incoming light is obstructed by this cage?

Accepted Answer

A) about 3% 
B) about 44% 
C) about 1/6, or 17% 
D) about 36% 
A) about 3% 
B) about 44% 
C) about 1/6, or 17% 
D) about 36%

Question 3

Which of the following wavelengths of electromagnetic radiation will not reach Earth's surface? (See Figure 6-25 of Universe, 11th ed.)
​
  ​

Accepted Answer

A) 10 m 
B) 100 μm 
C) 1 μm 
D) 10 cm 
A) 10 m 
B) 100 μm 
C) 1 μm 
D) 10 cm

Question 4

What is the magnification of a Newtonian telescope with a primary mirror of diameter 0.25 m and focal length of 4 m when used with an eyepiece of focal length 25 mm and an optical diameter of 2.5 mm?

Accepted Answer

A) 100 
B) 160 
C) 10 
D) 1600 
A) 100 
B) 160 
C) 10 
D) 1600

Question 5

Over what range of wavelengths does the Hubble Space Telescope operate?

Accepted Answer

A) only visible and ultraviolet 
B) visible only 
C) infrared, visible, and ultraviolet 
D) only visible and infrared 
A) only visible and ultraviolet 
B) visible only 
C) infrared, visible, and ultraviolet 
D) only visible and infrared

Question 6

The magnifying power of a reflecting telescope, in terms of the focal length F of the primary mirror and the focal length f the eyepiece, (with F and f measured in the same units), is:

Accepted Answer

A) fF. 
B) f/F. 
C) F/f 2. 
D) F/f. 
A) fF. 
B) f/F. 
C) F/f 2. 
D) F/f.

Question 7

If all effects caused by Earth's atmospheric variations (seeing) could be removed from the visible image of a star on one of the 10-m diameter Keck telescopes on Hawaii, what would be the angular resolution achievable by this telescope in arcseconds for light of wavelength 500 nm? (1 nm = 10-9 m)

Accepted Answer

A) 0.00125 arcsec 
B) 0.125 arcsec 
C) 12.5 arcsec 
D) 0.0125 arcsec 
A) 0.00125 arcsec 
B) 0.125 arcsec 
C) 12.5 arcsec 
D) 0.0125 arcsec

Question 8

The James Webb Space Telescope will be placed in orbit:

Accepted Answer

A) around the Moon. 
B) around Earth. 
C) around the Sun. 
D) at a fixed point in space, not orbiting anything. 
A) around the Moon. 
B) around Earth. 
C) around the Sun. 
D) at a fixed point in space, not orbiting anything.

Question 9

A particular reflecting telescope has a primary mirror 0.4 m in diameter, 2.0 m focal length, and an eyepiece lens 1.0 cm in diameter and 0.5 cm focal length. What is the magnifying power of this telescope?

Accepted Answer

A) 400× 
B) 40× 
C) 4× 
D) 80× 
A) 400× 
B) 40× 
C) 4× 
D) 80×

Question 10

If a beam of waves passes through a narrow opening, like the optics of a telescope, the beam will be seen to diverge and not just continue in the original direction. This is a consequence of:

Accepted Answer

A) diffraction. 
B) refraction. 
C) reflection. 
D) chromatic aberration. 
A) diffraction. 
B) refraction. 
C) reflection. 
D) chromatic aberration.

Question 11

A reflecting telescope in which light is reflected by one curved mirror and a second plane mirror at 45° to the original beam, to reach a focus at the side of the telescope, is being used at its:

Accepted Answer

A) Newtonian focus. 
B) out-of-focus position. 
C) prime focus. 
D) Cassegrain focus. 
A) Newtonian focus. 
B) out-of-focus position. 
C) prime focus. 
D) Cassegrain focus.

Question 12

Suppose the four 8.2-m mirrors of the Very Large Telescope were replaced with 10-m mirrors, but they were still spread out over a distance of 200 m. The combined light-gathering power would be equivalent to that of a single telescope of what diameter?

Accepted Answer

A) 16.4 m 
B) 20 m 
C) 40 m 
D) 200 m 
A) 16.4 m 
B) 20 m 
C) 40 m 
D) 200 m

Question 13

A light ray strikes a smooth surface of glass at an angle α to the perpendicular. What angle will the reflected ray make with the perpendicular to the surface?

Accepted Answer

A) 2α on the opposite side of the perpendicular to the incident ray 
B) 0°; the ray will always reflect along the perpendicular, a condition necessary for the focusing of light. 
C) the same angle α on the opposite side of the perpendicular to the incident ray 
D) the same angle α on the same side of the perpendicular, returning along the incident direction 
A) 2α on the opposite side of the perpendicular to the incident ray 
B) 0°; the ray will always reflect along the perpendicular, a condition necessary for the focusing of light. 
C) the same angle α on the opposite side of the perpendicular to the incident ray 
D) the same angle α on the same side of the perpendicular, returning along the incident direction

Question 14

The angular resolution of a radio telescope with a baseline equal to the diameter of Earth is given as 0.001 arcsec. What wavelength is being used for the calculation?

Accepted Answer

A) 0.02 m 
B) 0.05 m 
C) 0.5 m 
D) 20 m 
A) 0.02 m 
B) 0.05 m 
C) 0.5 m 
D) 20 m

Question 15

The first true radio telescope, built by Grote Reber to map radio emissions from the center of the Milky Way, was built in:

Accepted Answer

A) 1980. 
B) 1946. 
C) 1932. 
D) 1936. 
A) 1980. 
B) 1946. 
C) 1932. 
D) 1936.

Question 16

What angular resolution is possible with the Keck telescopes when light from both telescopes is combined? (Assume observations are made in visible light at 500 nm wavelength.)

Accepted Answer

A) 1/20,000 arcsec 
B) 1/200 arcsec 
C) 1/2000 arcsec 
D) 1/5 arcsec (limited by atmospheric turbulence, or "seeing") 
A) 1/20,000 arcsec 
B) 1/200 arcsec 
C) 1/2000 arcsec 
D) 1/5 arcsec (limited by atmospheric turbulence, or "seeing")

Question 17

How does the angular resolution of the 305-m Arecibo radio telescope in Puerto Rico compare with the angular resolution of the 10-m Keck optical telescope on Mauna Kea, Hawaii?

Accepted Answer

A) They have about the same angular resolution, since angular resolution is limited by turbulence in Earth's atmosphere, not by mirror diameter. 
B) The 305-m telescope has much worse angular resolution than the 10-m Keck telescope. 
C) It is not possible to compare their angular resolution, since they work in different wavelength ranges. 
D) The 305-m telescope has much better angular resolution than the 10-m Keck telescope. 
A) They have about the same angular resolution, since angular resolution is limited by turbulence in Earth's atmosphere, not by mirror diameter. 
B) The 305-m telescope has much worse angular resolution than the 10-m Keck telescope. 
C) It is not possible to compare their angular resolution, since they work in different wavelength ranges. 
D) The 305-m telescope has much better angular resolution than the 10-m Keck telescope.

Question 18

The constituents of the atmosphere that absorb most strongly at infrared wavelengths, limiting our ability to observe astronomical infrared objects from the surface of Earth, is (are):

Accepted Answer

A) dust. 
B) N2 and O2, the major constituents of the atmosphere. 
C) electrons and ionized atoms in Earth's ionosphere. 
D) water vapor, H2O. 
A) dust. 
B) N2 and O2, the major constituents of the atmosphere. 
C) electrons and ionized atoms in Earth's ionosphere. 
D) water vapor, H2O.

Question 19

Placing a small 45° mirror in the path of the light from the objective mirror in a reflecting telescope (as Newton did) does all of the following except one. Which one is not a consequence of this method?

Accepted Answer

A) It makes the telescope easier to use compared to a prime focus. 
B) It introduces the possibility of distortion in the secondary mirror. 
C) It decreases the amount of light reaching the objective mirror. 
D) It causes a blank spot in the image where the beam has been interrupted by the secondary mirror. 
A) It makes the telescope easier to use compared to a prime focus. 
B) It introduces the possibility of distortion in the secondary mirror. 
C) It decreases the amount of light reaching the objective mirror. 
D) It causes a blank spot in the image where the beam has been interrupted by the secondary mirror.

Question 20

The Herschel Space Observatory detects radiation in which region of the electromagnetic spectrum?

Accepted Answer

A) infrared 
B) visible 
C) ultraviolet 
D) gamma ray 
A) infrared 
B) visible 
C) ultraviolet 
D) gamma ray

Exam 6: Optics and Telescopes

One way to improve the angular resolution of a radio telescope is to:

The prime focus cage of a telescope whose primary mirror is 3 m in diameter has a diameter of 0.5 m. What fraction of the incoming light is obstructed by this cage?

Which of the following wavelengths of electromagnetic radiation will not reach Earth's surface? (See Figure 6-25 of Universe, 11th ed.) ​ ​

What is the magnification of a Newtonian telescope with a primary mirror of diameter 0.25 m and focal length of 4 m when used with an eyepiece of focal length 25 mm and an optical diameter of 2.5 mm?

Over what range of wavelengths does the Hubble Space Telescope operate?

The magnifying power of a reflecting telescope, in terms of the focal length F of the primary mirror and the focal length f the eyepiece, (with F and f measured in the same units), is:

If all effects caused by Earth's atmospheric variations (seeing) could be removed from the visible image of a star on one of the 10-m diameter Keck telescopes on Hawaii, what would be the angular resolution achievable by this telescope in arcseconds for light of wavelength 500 nm? (1 nm = 10-9 m)

The James Webb Space Telescope will be placed in orbit:

A particular reflecting telescope has a primary mirror 0.4 m in diameter, 2.0 m focal length, and an eyepiece lens 1.0 cm in diameter and 0.5 cm focal length. What is the magnifying power of this telescope?

If a beam of waves passes through a narrow opening, like the optics of a telescope, the beam will be seen to diverge and not just continue in the original direction. This is a consequence of:

A reflecting telescope in which light is reflected by one curved mirror and a second plane mirror at 45° to the original beam, to reach a focus at the side of the telescope, is being used at its:

Suppose the four 8.2-m mirrors of the Very Large Telescope were replaced with 10-m mirrors, but they were still spread out over a distance of 200 m. The combined light-gathering power would be equivalent to that of a single telescope of what diameter?

A light ray strikes a smooth surface of glass at an angle α to the perpendicular. What angle will the reflected ray make with the perpendicular to the surface?

The angular resolution of a radio telescope with a baseline equal to the diameter of Earth is given as 0.001 arcsec. What wavelength is being used for the calculation?

The first true radio telescope, built by Grote Reber to map radio emissions from the center of the Milky Way, was built in:

What angular resolution is possible with the Keck telescopes when light from both telescopes is combined? (Assume observations are made in visible light at 500 nm wavelength.)

How does the angular resolution of the 305-m Arecibo radio telescope in Puerto Rico compare with the angular resolution of the 10-m Keck optical telescope on Mauna Kea, Hawaii?

The constituents of the atmosphere that absorb most strongly at infrared wavelengths, limiting our ability to observe astronomical infrared objects from the surface of Earth, is (are):

Placing a small 45° mirror in the path of the light from the objective mirror in a reflecting telescope (as Newton did) does all of the following except one. Which one is not a consequence of this method?

The Herschel Space Observatory detects radiation in which region of the electromagnetic spectrum?

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

Filters

Which of the following wavelengths of electromagnetic radiation will not reach Earth's surface? (See Figure 6-25 of Universe, 11th ed.)

If all effects caused by Earth's atmospheric variations (seeing) could be removed from the visible image of a star on one of the 10-m diameter Keck telescopes on Hawaii, what would be the angular resolution achievable by this telescope in arcseconds for light of wavelength 500 nm? (1 nm = 10^-9 m)