Telescopes
Most popular depictions in TV shows and movies portray an astronomer as someone who spends most nights in a cold observatory looking through a telescope, but this is not very accurate today. Most astronomers do not live at observatories but near the universities or laboratories where they work. An astronomer might only spend a week or so each year observing at the telescope and the rest of the time measuring or analyzing the data acquired from large projects or surveys. Many astronomers use radio telescopes for space experiments, which work just as well during the daylight hours. Still, others work on purely theoretical problems using supercomputers and never observe at a telescope of any kind.
Even when astronomers are observing with large telescopes, they rarely peer through them. Electronic detectors permanently record the data for detailed analysis later. At some observatories, observations may be made remotely, with the astronomer sitting at a computer thousands of miles away from the telescope.
Telescopes used by modern-day astronomers are large and sophisticated machines that sometimes cost up to $100 million to build. That kind of investment demands that the telescope be placed in the best possible site. Earth’s atmosphere, so vital to life, presents challenges for the observational astronomer, so there are a few conditions that astronomers look for when picking a site for an observatory.
The most obvious limitation is weather conditions such as clouds, wind, and rain. At the best sites, where most telescopes are located, the weather is clear as much as 75% of the time. Still, even on a clear night, the atmosphere filters out a certain amount of starlight. Astronomers, therefore, prefer dry sites with little water vapor, which is generally found at higher altitudes. The sky above the telescope should be dark. Near cities, the air scatters the glare from lights, producing an illumination that hides the faintest stars and limits the distances that can be probed by telescopes. Observatories are best located at least 100 miles from the nearest large city. The best observatory sites are, therefore, high, dark, and dry. The world’s largest telescopes are found in such remote mountain locations as the Andes Mountains of Chile, the desert peaks of Arizona, and Mauna Kea in Hawaii, a dormant volcano.
In addition to gathering as much light as they can, astronomers also want to have the sharpest images possible. Resolution refers to the precision of detail present in an image, that is, the smallest features that can be distinguished. Astronomers are always eager to make out more detail in the images they study, whether they are following the weather on Jupiter or trying to peer into a galaxy that recently ate its neighbor for lunch. One factor that determines how good the resolution will be is the size of the telescope. Larger apertures produce sharper images. Until very recently, however, telescopes on Earth’s surface could not produce images as sharply as the theory of light said they should.
The problem is our planet’s atmosphere. It contains many small pockets of cell gas that range in size from inches to several feet. Each cell has a slightly different temperature from its neighbor, and each cell acts like a lens, bending (refracting) the path of the light by a small amount. This bending slightly changes the position where each light ray finally reaches the telescope. The cells of air are in motion, constantly being blown through the light path of the telescope by winds, often in different directions at different altitudes. As a result, the path followed by the light is constantly changing.
Astronomers have devised a technique called adaptive optics that can beat Earth’s atmosphere at its own game of blurring. This technique makes use of a small flexible mirror placed in the beam of a telescope. A sensor measures how much the atmosphere has distorted the image, and as often as 500 times per second, it sends instructions to the flexible mirror on how to change shape in order to compensate for distortions produced by the atmosphere. The light is thus brought back to an almost perfectly sharp focus.
Source: Beck, J. et al., (2016).
Reading Paragraph 1
Most popular depictions in TV shows and movies portray an astronomer as someone who spends most nights in a cold observatory looking through a telescope, but this is not very accurate today. Most astronomers do not live at observatories but near the universities or laboratories where they work. An astronomer might spend only a week or so each year observing at the telescope and the rest of the time measuring or analyzing the data acquired from large projects or surveys. Many astronomers use radio telescopes for space experiments, which work just as well during the daylight hours. Still, others work on purely theoretical problems using supercomputers and never observe at a telescope of any kind.
1. What does the author say about astronomers in the first paragraph?
a. Most of their time is spent making observations through telescopes
b. Those who work on theoretical problems never use telescopes
c. Most live at observatories in order to look through telescopes at night
d. Many do not have time to measure and analyze data on their space experiments
Reading Paragraph 3
Telescopes used by modern-day astronomers are large and sophisticated machines that sometimes cost up to $100 million to build. That kind of investment demands that the telescope be placed in the best possible site. Earth’s atmosphere, so vital to life, presents challenges for the observational astronomer, so there are a few conditions that astronomers look for when picking a site for an observatory.
2. In the third paragraph, what does the author point out about telescopes?
a. That they are usually invested in by universities and labs
b. That they are always $100 million to build
c. That most are very high-tech and economical
d. That they need to be placed in the most advantageous location
3. Which of the following best expresses the essential information in the highlighted sentence in paragraph 3? Incorrect choices change the meaning in important ways or leave out essential information.
a. The atmosphere creates challenges for astronomers to find a site for observatories on Earth
b. Earth’s atmosphere has conditions that astronomers must analyze before viewing space through a telescope
c. Astronomers have factors to consider when choosing an observatory’s site because of the Earth’s atmosphere
d. Observational astronomers look at weather conditions when they pick the site for an observatory
Reading Paragraph 4
The most obvious limitation is weather conditions such as clouds, wind, and rain. At the best sites, where most telescopes are located, the weather is clear as much as 75% of the time. Still, even on a clear night, the atmosphere filters out a certain amount of starlight. Astronomers, therefore, prefer dry sites with little water vapor, which is generally found at higher altitudes. The sky above the telescope should be dark. Near cities, the air scatters the glare from lights, producing an illumination that hides the faintest stars and limits the distances that can be probed by telescopes. Observatories are best located at least 100 miles from the nearest large city. The best observatory sites are, therefore, high, dark, and dry. The world’s largest telescopes are found in such remote mountain locations as the Andes Mountains of Chile, the desert peaks of Arizona, and Mauna Kea in Hawaii, a dormant volcano.
4. Which of the following is NOT mentioned in paragraph 4?
a. There are large telescopes in Arizona and Hawaii
b. The atmosphere separates out some starlight in telescopes
c. Telescopes are best located where the weather is clear the majority of the time
d. The worse place for telescopes is in tropical climates near the ocean
Reading Paragraph 5
In addition to gathering as much light as they can, astronomers also want to have the sharpest images possible. Resolution refers to the precision of detail present in an image, that is, the smallest features that can be distinguished. Astronomers are always eager to make out more detail in the images they study, whether they are following the weather on Jupiter or trying to peer into a galaxy that recently ate its neighbor for lunch. One factor that determines how good the resolution will be is the size of the telescope. Larger apertures produce sharper images. Until very recently, however, telescopes on Earth’s surface could not produce images as sharp as the theory of light said they should.
5. Why does the author mention “a galaxy that recently ate its neighbor for lunch” in paragraph 5?
a. To explain how much detail high-quality resolutions can show
b. To illustrate an exciting observation using a metaphor
c. To provide a comprehensive list of the different uses of the telescope by astronomers
d. To show why a previously existing galaxy is no more
Reading Paragraph 5
In addition to gathering as much light as they can, astronomers also want to have the sharpest images possible. Resolution refers to the precision of detail present in an image: that is, the smallest features that can be distinguished. Astronomers are always eager to make out more detail in the images they study, whether they are following the weather on Jupiter or trying to peer into a galaxy that recently ate its neighbor for lunch. One factor that determines how good the resolution will be is the size of the telescope. Larger apertures produce sharper images. Until very recently, however, telescopes on Earth’s surface could not produce images as sharply as the theory of light said they should.
6. According to paragraph 5, what does the author say about resolution?
a. It can only show the small details in an image when it is up close
b. It cannot create sharp images if there is too much light
c. It does not work on telescopes on the Earth’s surface
d. It is sharper on telescopes with bigger openings
Reading Paragraph 6
The problem is our planet’s atmosphere. It contains many small pockets of cell gas that range in size from inches to several feet. Each cell has a slightly different temperature from its neighbor, and each cell acts like a lens, bending (refracting) the path of the light by a small amount. This bending slightly changes the position where each light ray finally reaches the telescope. The cells of air are in motion, constantly being blown through the light path of the telescope by winds, often in different directions at different altitudes. As a result, the path followed by the light is constantly changing.
7. In paragraph 6, the author says as a result in order to
a. To provide the cause for why the light path is constantly changing
b. To define the reason the wind blows the light paths in different directions
c. To explain the effect of the cells of air constantly being blown by the winds through light paths
d. To describe one problem with the Earth’s atmosphere
Reading Paragraph 7
Astronomers have devised a technique called adaptive optics that can beat Earth’s atmosphere at its own game of blurring. This technique makes use of a small flexible mirror placed in the beam of a telescope. A sensor measures how much the atmosphere has distorted the image, and as often as 500 times per second, it sends instructions to the flexible mirror on how to change shape in order to compensate for distortions produced by the atmosphere. The light is thus brought back to an almost perfectly sharp focus.
8. In paragraph 7, the word distorted is closest in meaning to
a. Ruined
b. Corrected
c. Diluted
d. Altered
9. Look at the four squares (A, B, C, D) that indicate where the following sentence could be added to the passage.
The Extremely Large Telescope, which will be five times larger than the world’s largest telescope, is currently under construction in the driest desert in the world, the Atacama Desert in Chile.
Where would the sentence best fit?
The most obvious limitation is weather conditions such as clouds, wind, and rain. At the best sites, where most telescopes are located, the weather is clear as much as 75% of the time. A Still, even on a clear night, the atmosphere filters out a certain amount of starlight. Astronomers, therefore, prefer dry sites with little water vapor, which is generally found at higher altitudes. The sky above the telescope should be dark. B Near cities, the air scatters the glare from lights, producing an illumination that hides the faintest stars and limits the distances that can be probed by telescopes. C Observatories are best located at least 100 miles from the nearest large city. The best observatory sites are, therefore, high, dark, and dry. The world’s largest telescopes are found in such remote mountain locations as the Andes Mountains of Chile, the desert peaks of Arizona, and Mauna Kea in Hawaii, a dormant volcano. D
10. DIRECTIONS: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Telescopes have evolved and improved over the years, as has the relationship astronomers have with these powerful machines.
a. Sometimes astronomers can work thousands of miles away from observatories
b. Large telescopes with large openings can be very expensive to build
c. The lights produced by big cities make it impossible to see through telescopes
d. Light paths in the atmosphere change with the season creating challenges for smaller telescopes
e. Adaptive optics, invented by Horace Babcock in 1953, allows astronomers to see images in sharp focus
f. The best placements for telescopes are in remote, high, dry, and dark locations
