Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Chapter 6, Problem 31E
People are often bothered when they discover that reflecting telescopes have a second mirror in the middle to bring the light out to an accessible focus where big instruments can be mounted. “Don’t you lose light?” people ask. Well, yes, you do, but there is no better alternative. You can estimate how much light is lost by such an arrangement. The primary mirror (the one at the bottom in Figure 6.6) of the Gemini North telescope is 8 m in diameter. The secondary mirror at the top is about 1 m in diameter. Use the formula for the area of a circle to estimate what fraction of the light is blocked by the secondary mirror.
Figure 6.6 Focus Arrangements for Reflecting Telescopes. Reflecting telescopes have different options for where the light is brought to a focus. With prime focus, light is detected where it comes to a focus after reflecting from the primary mirror. With Newtonian focus, light is reflected by a small secondary mirror off to one side, where it can be detected (see also Figure 6.5). Most large professional telescopes have a Cassegrain focus in which light is reflected by the secondary mirror down through a hole in the primary mirror to an observing station below the telescope.
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What is the magnification of an astronomical telescope whose objective lens has a focal length of 78 cm and whose eyepiece has a focal length of 2.8 cm? The telescope is set so the image of the eyepiece is at infinity (so the viewer’s eye is “relaxed”). What is the overall length of the telescope?
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A Cassegrain telescope is a reflecting
telescope that uses two mirrors, the secondary
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cm.
Figure 1
of 1
Secondary
Primary
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Part A
What should be the distance between the
vertices of the two mirrors?
Express your answer using two
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Look at the central transparent area of someone’s eye, the pupil, in normal room light. Estimate the diameter of the pupil. Now turn off the lights and darken the room. After a few minutes turn on the lights and promptly estimate the diameter of the pupil. What happens to the pupil as the eye adjusts to the room light? Explain your observations.
Chapter 6 Solutions
Astronomy
Ch. 6 - What are the three basic components of a modern...Ch. 6 - Name the two spectral windows through which...Ch. 6 - List the largest-aperture single telescope...Ch. 6 - When astronomers discuss the apertures of their...Ch. 6 - The Hooker telescope at Palomar Observatory has a...Ch. 6 - What is meant by “reflecting” and “refracting”...Ch. 6 - Why are the largest visible-light telescopes in...Ch. 6 - Compare the eye, photographic film, and CCDs as...Ch. 6 - What is a charge-coupled device (CCD), and how is...Ch. 6 - Why is it difficult to observe at infrared...
Ch. 6 - Radio and radar observations are often made with...Ch. 6 - Look back at Figure 6.18 of Cygnus A and read its...Ch. 6 - Why do astronomers place telescopes in Earth’s...Ch. 6 - What was the problem with the Hubble Space...Ch. 6 - Describe the techniques radio astronomers use to...Ch. 6 - What kind of visible-light and infrared telescopes...Ch. 6 - Describe one visible-light or infrared telescope...Ch. 6 - What happens to the image produced by a lens if...Ch. 6 - What would be the properties of an ideal...Ch. 6 - Many decades ago, the astronomers on the staff of...Ch. 6 - The largest observatory complex in the world is on...Ch. 6 - Suppose you are looking for sites for a...Ch. 6 - Radio astronomy involves wavelengths much longer...Ch. 6 - The dean of a university located near the ocean...Ch. 6 - What is the area, in square meters, of a 10-m...Ch. 6 - Approximately 9000 stars are visible to the naked...Ch. 6 - Theoretically (that is, if seeing were not an...Ch. 6 - In broad daylight, the size of your pupil is...Ch. 6 - How much more light can be gathered by a telescope...Ch. 6 - How much more light can the Keck telescope (with...Ch. 6 - People are often bothered when they discover that...Ch. 6 - Telescopes can now be operated remotely from a...Ch. 6 - The HST cost about $1.7 billion for construction...Ch. 6 - How much more light can the James Webb Space...Ch. 6 - The Palomar telescope’s 5-m mirror weighs 14.5...
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