Question 1

Telescopes designed to observe infrared radiation

Accepted Answer

A)  must be placed in orbit above Earth's atmosphere. 
B)  can be placed on Earth's surface as long as the altitude is high enough to avoid water vapor, the prime absorber of infrared radiation in the atmosphere. 
C)  can be placed on Earth's surface as long as the altitude is high enough to avoid carbon dioxide, the prime absorber of infrared radiation in the atmosphere. 
D)  can be placed at any convenient location on Earth's surface because infrared radiation penetrates one of the "windows" of transparency in the atmosphere.

Question 2

The primary mirrors in the 10-m Keck telescopes consist of

Accepted Answer

A)  a large hollow honeycomb of glass-lightweight but relatively thick to prevent sagging. 
B)  a large, thin slab of glass whose surface is continuously adjusted by computer-controlled motors. 
C)  six individual mirrors, mounted so that they all bring the light to the same focus. 
D)  36 individual mirrors, mounted so that they all bring the light to the same focus.

Question 3

Compared with the 2.5-m diameter Mount Wilson telescope, each of the 10-m diameter Keck telescopes has a greater light-gathering power by a factor of

Accepted Answer

A)  4. 
B)  16. 
C)  2. 
D)  1; they have the same light-gathering capability.

Question 4

A particular telescope is set up to use the coudé focus. Which arrangement of mirrors is used to bring the light to this focus?

Accepted Answer

A)  curved primary mirror followed by a series of plane and curved mirrors that channel the light to a remote and fixed location 
B)  concave primary mirror followed by a convex secondary mirror that reflects light through a hole in the primary mirror 
C)  concave primary mirror followed by a concave secondary mirror that reflects light through a hole in the primary mirror 
D)  concave primary mirror and a flat, diagonal secondary mirror mounted at a 45° angle to the telescope axis

Question 5

The main use of the Schmidt-type telescope, which uses a spherical primary mirror and a refracting "corrector plate," is for

Accepted Answer

A)  narrow field-of-view photography and photometry. 
B)  single-star spectroscopy. 
C)  wide-angle photography for sky surveys. 
D)  radio astronomy.

Question 6

The angle between two adjacent stars whose images can just barely be distinguished by the telescope is a measure of the telescope's

Accepted Answer

A)  light-gathering power. 
B)  resolution. 
C)  magnification. 
D)  coudé focus.

Question 7

Suppose an astronomical satellite observes the Crab Nebula at a wavelength of 0.85 nm. In what wavelength range is this satellite observing?

Accepted Answer

A)  X-ray 
B)  ultraviolet 
C)  Infrared 
D)  gamma ray

Question 8

A high mountaintop such as Mauna Kea in Hawaii is a good site for an infrared observatory primarily because it is

Accepted Answer

A)  above the absorbing ozone layer. 
B)  farther from city lights. 
C)  above a significant proportion of the moisture in Earth's atmosphere. 
D)  above most of the turbulence in Earth's atmosphere.

Question 9

Which of these wavelength regions must be observed from space because almost no energy in this region reaches the ground?

Accepted Answer

A)  radio 
B)  infrared 
C)  X-rays 
D)  visible light

Question 10

Which method did Ole Rømer use to show that light did not travel at infinite speed?

Accepted Answer

A)  Rømer observed that eclipses of Jupiter's satellites by the planet appeared to occur later when Earth was farther away from Jupiter because of the travel time for light over the extra distance. 
B)  Rømer measured a time delay between the instant that he sent a flash of light to a mirror on a distant hill and the return of the flash after reflection. 
C)  Rømer carried out a laboratory experiment in which a light beam was sent through an opaque, rotating disk with holes in it and reflected from a distant mirror, where the returning beam did not return through the same hole from which it left because of the travel time for light. 
D)  Rømer measured a 2 $1 / 2$ -second delay between the time of the outgoing pulse of light sent from Earth to the Moon and the time of the returning light pulse after reflection from the Moon.

Question 11

The neutrino is

Accepted Answer

A)  a tiny particle that interacts very weakly with matter, with extremely low mass and no charge. 
B)  another name for the neutron, a component of almost all atomic nuclei, with a mass close to that of the proton and having no charge. 
C)  another name for a photon of very high-energy (i.e., short-wavelength) electromagnetic radiation with great penetrating power. 
D)  a massive but very elusive nuclear particle that carries most of the energy generated in the core of the Sun to the surface, but then decays to release electromagnetic radiation (i.e., light).

Question 12

Approximately how long does it take light to travel from the fingertips of a person's extended arm to one's eye?

Accepted Answer

A)  zero time because light is transmitted instantaneously 
B)  2.5 trillionths of a second (2.5 × 10-12 sec) 
C)  2.5 billionths of a second (2.5 nanoseconds) 
D)  2.5 millionths of a second (2.5 microseconds)

Question 13

The speed of light is

Accepted Answer

A)  3 × 1010 m/sec. 
B)  3 × 108 m/sec. 
C)  3 × 1012 m/sec. 
D)  3 × 105 m/sec.

Question 14

When a light ray in air or a vacuum hits the surface of a piece of perfectly smooth, flat glass at an angle and enters the glass, it will

Accepted Answer

A)  reverse its direction and return along its original path. 
B)  bend toward the perpendicular to the surface. 
C)  bend away from the perpendicular to the surface. 
D)  not change its direction at all.

Question 15

What percentage of the light falling on the BEST CCD's is typically wasted (does not contribute to the formation of the image)?

Accepted Answer

A)  1% 
B)  10% 
C)  90% 
D)  98%

Question 16

What is chromatic aberration in a telescope?

Accepted Answer

A)  Light of different colors reflecting from the objective mirror of the telescope comes to a focus at different points in front of the mirror. 
B)  Light of different colors comes to a focus at different points behind the objective lens inside the telescope. 
C)  Light striking the lens at different distances from the center of the lens comes to a focus at different points inside the telescope. 
D)  The objective lens varies in thickness from center to edge, and light passing through the different thicknesses suffers different amounts of absorption, thereby coloring the image.

Question 17

Our present understanding of the nature of light is that it

Accepted Answer

A)  behaves only as a wave. 
B)  behaves only as a particle. 
C)  displays behavior of both waves and particles. 
D)  is completely different from both waves and particles.

Question 18

As a light ray leaves a glass surface, traveling from the glass back into air at an angle to the surface, the light ray

Accepted Answer

A)  bends away from the perpendicular to the surface. 
B)  bends so that it travels exactly along the perpendicular to the surface. 
C)  bends toward the perpendicular to the surface. 
D)  travels in a straight line without bending.

Question 19

How is spherical aberration eliminated in a reflecting telescope?

Accepted Answer

A)  by using the Cassegrain focus of the telescope 
B)  by making the primary mirror very thin 
C)  by grinding the primary mirror surface to a parabolic shape 
D)  by bending the photographic film into a concave shape

Question 20

Which combination of optics is used in the Schmidt-Cassegrain telescope for producing high-quality wide-angle images of the sky?

Accepted Answer

A)  single, short-focal-length spherical mirror 
B)  parabolic mirror of short focal length, used at prime focus 
C)  two lenses of different glass, one convex, the other concave, to reduce chromatic aberration 
D)  spherical primary mirror with a thin correcting lens ahead of it

Exam 3: Light and Telescopes