Question 1

It is difficult to improve the angular resolution of optical telescopes located on the surface of Earth beyond a certain limit because
A) large telescopes are reflecting telescopes, and they suffer from too much chromatic aberration.
B) spherical mirrors suffer from too much aberration.
C) star images are distorted more by air turbulence than by the telescope optics.
D) improvement would require much larger, very expensive telescopes to enhance the inherent telescope.

Accepted Answer

Air turbulence in the Earth's atmosphere distorts the images of stars more than the optics of the telescope itself, limiting the angular resolution of ground-based optical telescopes. This phenomenon is known as atmospheric seeing.

Question 2

The sharpest images of stars that can be formed by a single, large, ground-based, visible-light telescope are of the order of what angular size? A) about 10^-3 arcsecond B) about 1° C) about 1 arcminute D) about 0.2 arcsecond

Accepted Answer

The sharpest images of stars formed by a large, ground-based, visible-light telescope are limited by the Earth's atmosphere to about 0.2 arcsecond in angular size. This limitation is due to atmospheric turbulence, which distorts the light coming from stars and other celestial objects.

Question 3

What is the angular resolution of the Hubble Space Telescope?
A) 0.01 arcsecond
B) 0.001 arcsecond
C) 1 arcsecond
D) 0.1 arcsecond

Accepted Answer

The answer of What is the angular resolution of the...

Question 4

What does the word "seeing" mean to an astronomer using a telescope?
A) twinkling and blurring of the image due to turbulence in Earth's atmosphere
B) combined effects of aberrations in the components of the telescope, particularly spherical and chromatic aberration
C) effect of wind on the telescope that causes it to vibrate, thereby blurring the image
D) haze or thin cloud in the atmosphere that reduces the brightness and sharpness of the telescope image

Accepted Answer

"Seeing" in astronomy refers to the twinkling and blurring of images caused by turbulence in Earth's atmosphere, which affects the clarity of observations made through telescopes.

Question 5

Images from the 5-meter telescope at Mount Palomar are not as clear as they were when the telescope was first put into operation over 60 years ago. Why is this?
A) The quality of the mirror has degraded significantly over time.
B) Precession has changed the positions of a number of important targets so that they are no longer accessible from Palomar.
C) The telescope was recently damaged by an earthquake.
D) Light pollution has increased significantly in the past 60 years.

Accepted Answer

Light pollution has increased significantly in the past 60 years, affecting the clarity of images captured by the telescope.

Question 6

One technique that astronomers are now using to increase the amount of detail that can be recorded with telescopes is
A) spinning huge tubs of mercury, thus producing very large parabolic surfaces at relatively low cost.
B) antireflective coatings, where the mirror is coated with a substance such as calcium fluorite to reduce the amount of reflected light.
C) increased size, with mirrors up to 10 m in diameter (far larger than at earlier times), thereby producing greater intrinsic angular resolution.
D) adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per second to compensate for atmospheric turbulence.

Accepted Answer

Adaptive optics is a technique used to improve the resolution of telescopes by adjusting the mirrors in real-time to counteract the blurring effects of Earth's atmosphere.

Question 7

Why was adaptive optics developed?
A) to prevent the distortion of mirrors by the vacuum of space
B) to compensate for image distortion caused by Earth's atmosphere
C) to compensate for spherical aberration
D) to prevent distortion by sagging in very thin, lightweight mirrors

Accepted Answer

Adaptive optics was developed to compensate for image distortion caused by Earth's atmosphere. This technology adjusts the optics in real-time to counteract the blurring effects of the Earth's atmosphere, allowing for clearer images of celestial objects.

Question 8

The Hubble Space Telescope, placed in orbit by the space shuttle Discovery in 1990, has a primary mirror of diameter
A) 57 m.
B) 1 m.
C) 6 m.
D) 2.4 m.

Accepted Answer

The Hubble Space Telescope has a primary mirror diameter of 2.4 meters, which has allowed it to capture high-resolution images of space since its deployment.

Question 9

After the Hubble Space Telescope was launched, it was found to suffer seriously from
A) scattering of light from dust on the primary mirror surface.
B) too much angular resolution.
C) spherical aberration.
D) chromatic aberration.

Accepted Answer

The Hubble Space Telescope suffered from spherical aberration due to a flaw in the shape of its primary mirror, which affected the clarity of the images it initially produced.

Question 10

What factor has seriously reduced the effectiveness over the last few years of the 5-m Hale telescope on Mount Palomar, California, formerly the largest telescope in the world?
A) light pollution from nearby cities
B) cracking of the mirror by the Los Angeles earthquake
C) distortion of the mirror surface from repeated exposure to the cold night air on the mountain
D) tarnishing of the mirror surface by air pollution

Accepted Answer

Light pollution from nearby cities has significantly reduced the effectiveness of the Hale Telescope by increasing the background light, which makes it more difficult to observe faint astronomical objects.

Question 11

Which statement about the twinkling of stars and planets is NOT correct?
A) Stars twinkle less when they are farther from the horizon.
B) A photographic image of more than a few seconds exposure time will show a twinkling star as a disk.
C) Planets twinkle less than stars.
D) Twinkling of stars is an inherent phenomenon and cannot be reduced by any observing technique.

Accepted Answer

Twinkling of stars, also known as scintillation, is caused by the Earth's atmosphere distorting the light from the star. Advanced observing techniques, such as adaptive optics used in modern telescopes, can significantly reduce the effects of atmospheric distortion, thereby reducing the twinkling effect. This means that twinkling is not an inherent, unchangeable phenomenon.

Question 12

One way to distinguish a star from a planet, particularly when they appear near the horizon, is that stars appear to twinkle and planets shine steadily. Which of these statements is a reasonable explanation for this phenomenon?
A) Stars actually do twinkle-shine with a light that flickers bright and dim-whereas planets shine with a steady, unwavering light.
B) The light from planets is so much brighter than the light from stars (when they are observed from Earth) that it is unaffected by air movement in Earth's atmosphere.
C) The disk of a planet, as observed from Earth, appears larger than the disk of a star. Thus, if refraction through moving air in Earth's atmosphere makes the planet's disk appear to move about slightly, there will normally be a central part of the disk that shines steadily and does not appear to twinkle.
D) Because light from planets is reflected, it is unaffected by the refraction in Earth's atmosphere.

Accepted Answer

The explanation for why stars appear to twinkle and planets shine steadily is due to the apparent size of their disks from Earth. Stars, being much farther away, appear as point sources of light, making them more susceptible to atmospheric turbulence, which causes the twinkling effect. Planets, being closer, present a larger disk size, which means that even though parts of their light might be refracted by the atmosphere, there's always a portion of the disk that remains steady to the observer, leading to a steadier appearance.

Question 13

If one observatory site is described as having better "seeing" than another observatory site, what is it that is better at the first site?
A) The sky is more transparent and there is less haze in the atmosphere at that site, providing brighter and sharper images.
B) The winds are lighter at the better site, thereby producing less telescope vibration.
C) There is less air turbulence at that site, causing less twinkling and blurring of the images.
D) There are more clear nights at that site.

Accepted Answer

"Seeing" refers to the steadiness or turbulence of the Earth's atmosphere. Less air turbulence means less distortion of the light from stars and other celestial objects, resulting in clearer and sharper images.

Question 14

The Hubble Space Telescope is NOT designed to investigate
A) visible light.
B) ultraviolet radiation.
C) infrared radiation.
D) radio radiation.

Accepted Answer

The Hubble Space Telescope is designed to observe in the visible, ultraviolet, and near-infrared regions of the electromagnetic spectrum, but not in the radio spectrum.

Question 15

The BEST Earth-based sites for modern large astronomical telescopes, which provide the least seeing effects on astronomical images, are
A) near large cities, where the warm air from human activity serves to stabilize the overlying atmosphere.
B) at sea level, where the air is less turbulent.
C) on the downwind side of mountain ranges, where smooth airflow produces clear air and stable images.
D) on the tops of high mountains, above a large fraction of the disturbing atmosphere.

Accepted Answer

The best sites for large astronomical telescopes are on the tops of high mountains because these locations are above a significant portion of the Earth's atmosphere, which reduces atmospheric distortion and light pollution, leading to clearer and more stable images.

Question 16

What characteristic of the 10-m Keck telescopes makes them fundamentally different from older telescopes, such as the one on Mount Palomar?
A) They are located in Earth's orbit, away from all the distortions of Earth's atmosphere.
B) They are actually four closely spaced telescopes that can be operated together as if they were a single telescope.
C) The primary mirrors are large, very thin pieces of glass that can be deformed rapidly to compensate for seeing.
D) The primary mirror is made up of 36 separate mirror segments.

Accepted Answer

The primary mirror of the 10-m Keck telescopes is made up of 36 separate mirror segments, which is a fundamental difference from older telescopes like the one on Mount Palomar that have a single, solid primary mirror. This segmented design allows for the construction of much larger mirrors than would be possible with a single piece of glass.

Question 17

Adaptive optics involves
A) reconfiguration of the primary mirror to compensate for changes in telescope orientation and temperature.
B) reconfiguration of the primary mirror to compensate for atmospheric distortion.
C) reconfiguration of a secondary mirror to compensate for atmospheric distortion.
D) rapid switching among available eyepiece powers for optimal viewing of the target.

Accepted Answer

The answer of Adaptive optics involves
A) reconfiguration of the primary...

Question 18

Which of these techniques is the key factor in a telescope that uses adaptive optics to correct for atmospheric distortion of images, or "seeing"?
A) Computer-controlled motors rapidly adjust the orientation and position of the separate primary mirrors in a multiple-mirror telescope (MMT).
B) A corrector lens compensates for image distortion by electronic control of its shape.
C) Computer-controlled motors adjust the position and shape of one of the small mirrors within the optics many times per second.
D) The light rays are focused electronically, without the use of lenses or mirrors.

Accepted Answer

Adaptive optics systems use computer-controlled motors to adjust the position and shape of a deformable mirror in real-time, compensating for atmospheric distortion by altering the mirror's surface to correct the incoming light waves. This allows for much clearer images of celestial objects than would otherwise be possible through Earth's turbulent atmosphere.

Question 19

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

Accepted Answer

The primary mirrors of the 10-m Keck telescopes are made up of 36 individual hexagonal segments. These segments are mounted together to act as a single, large mirror, with each segment being adjusted in real time by computer-controlled systems to maintain the correct shape and focus. This design allows for a large collecting area without the weight and structural issues of a single, massive mirror.

Question 20

Which of these techniques has resulted in the BEST angular resolution of the image?
A) adaptive optics as used with Keck II on Mauna Kea
B) Hubble Space Telescope, an orbiting telescope
C) active optics, as used with the New Technology Telescope in Chile
D) interferometry, as used with the four telescopes of the Very Large Telescope (VLT) at the Paranel Observatory in Chile

Accepted Answer

Interferometry, especially when used with multiple telescopes like the VLT, allows for the highest angular resolution by effectively creating a telescope with a diameter as large as the distance between the individual telescopes. This technique surpasses the resolution limits of single mirrors or lenses, outperforming other methods listed.

Quiz 3: Light and Telescopes

It is difficult to improve the angular resolution of optical telescopes located on the surface of Earth beyond a certain limit because

The sharpest images of stars that can be formed by a single, large, ground-based, visible-light telescope are of the order of what angular size?

What is the angular resolution of the Hubble Space Telescope?

What does the word "seeing" mean to an astronomer using a telescope?

Images from the 5-meter telescope at Mount Palomar are not as clear as they were when the telescope was first put into operation over 60 years ago. Why is this?

One technique that astronomers are now using to increase the amount of detail that can be recorded with telescopes is

Why was adaptive optics developed?

The Hubble Space Telescope, placed in orbit by the space shuttle Discovery in 1990, has a primary mirror of diameter

After the Hubble Space Telescope was launched, it was found to suffer seriously from

What factor has seriously reduced the effectiveness over the last few years of the 5-m Hale telescope on Mount Palomar, California, formerly the largest telescope in the world?

Which statement about the twinkling of stars and planets is NOT correct?

One way to distinguish a star from a planet, particularly when they appear near the horizon, is that stars appear to twinkle and planets shine steadily. Which of these statements is a reasonable explanation for this phenomenon?

If one observatory site is described as having better "seeing" than another observatory site, what is it that is better at the first site?

The Hubble Space Telescope is NOT designed to investigate

The BEST Earth-based sites for modern large astronomical telescopes, which provide the least seeing effects on astronomical images, are

What characteristic of the 10-m Keck telescopes makes them fundamentally different from older telescopes, such as the one on Mount Palomar?

Adaptive optics involves

Which of these techniques is the key factor in a telescope that uses adaptive optics to correct for atmospheric distortion of images, or "seeing"?

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

Which of these techniques has resulted in the BEST angular resolution of the image?