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Chapter 5 Telescopes

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Chapter 5 Telescopes

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    1. Chapter 5 Telescopes Astronomers like to think big, and really big telescopes are now on the drawing board. This artist’s conception for the European Southern Observatory shows OWL, the OverWhelmingly Large telescope. With a mirror diameter of 100 meters, OWL would combine unrivaled light-gathering power with the ability to examine cosmic objects with unprecedented detail. This gargantuan project has an estimated cost of 1 billion Euros and would use building techniques pioneered in 1899 by Gustave Eiffel for his famous tower in Paris. (ESO)Astronomers like to think big, and really big telescopes are now on the drawing board. This artist’s conception for the European Southern Observatory shows OWL, the OverWhelmingly Large telescope. With a mirror diameter of 100 meters, OWL would combine unrivaled light-gathering power with the ability to examine cosmic objects with unprecedented detail. This gargantuan project has an estimated cost of 1 billion Euros and would use building techniques pioneered in 1899 by Gustave Eiffel for his famous tower in Paris. (ESO)

    2. 5.1 Optical Telescopes Figure 5-2. (a) Refraction by a prism changes the direction of a light ray by an amount that depends on the angle between the prism’s faces. When the angle between the faces is large, the deflection is large; when the angle is small, so is the deflection. (b) A lens can be thought of as a series of prisms. A light ray traveling along the axis of a lens is undeflected as it passes through the lens. Parallel rays arriving at progressively greater distances from the axis are refracted by increasing amounts in such a way that they all pass through a single point—the focus. Figure 5-2. (a) Refraction by a prism changes the direction of a light ray by an amount that depends on the angle between the prism’s faces. When the angle between the faces is large, the deflection is large; when the angle is small, so is the deflection. (b) A lens can be thought of as a series of prisms. A light ray traveling along the axis of a lens is undeflected as it passes through the lens. Parallel rays arriving at progressively greater distances from the axis are refracted by increasing amounts in such a way that they all pass through a single point—the focus.

    3. 5.1 Optical Telescopes Figure 5-3. (a) Reflection of light from a flat mirror occurs when light is deflected, depending on its angle of incidence. (b) A curved mirror can be used to focus to a single point all rays of light arriving parallel to the mirror axis. Light rays traveling along the axis are reflected back along the axis, as indicated by the arrowheads pointing in both directions. Off-axis rays are reflected through greater and greater angles the farther they are from the axis, so that they all pass through the focus. Figure 5-3. (a) Reflection of light from a flat mirror occurs when light is deflected, depending on its angle of incidence. (b) A curved mirror can be used to focus to a single point all rays of light arriving parallel to the mirror axis. Light rays traveling along the axis are reflected back along the axis, as indicated by the arrowheads pointing in both directions. Off-axis rays are reflected through greater and greater angles the farther they are from the axis, so that they all pass through the focus.

    4. 5.1 Optical Telescopes Figure 5.5 Comparison of (a) refracting and (b) reflecting telescopes. Both types are used to gather and focus electromagnetic radiation—to be observed by human eyes or recorded on photographs or in computers. In both cases, the image formed at the focus is viewed with a small magnifying lens called an eyepiece. Figure 5.5 Comparison of (a) refracting and (b) reflecting telescopes. Both types are used to gather and focus electromagnetic radiation—to be observed by human eyes or recorded on photographs or in computers. In both cases, the image formed at the focus is viewed with a small magnifying lens called an eyepiece.

    5. 5.1 Optical Telescopes

    6. 5.1 Optical Telescopes Figure 5.6 Four reflecting telescope designs: (a) prime focus, (b) Newtonian focus, (c) Cassegrain focus, and (d) Nasmyth/coudé focus. Each design uses a primary mirror at the bottom of the telescope to capture radiation, which is then directed along different paths for analysis. Notice that the secondary mirrors shown in (c) and (d) are actually slightly diverging, so that they move the focus outside the telescope. Figure 5.6 Four reflecting telescope designs: (a) prime focus, (b) Newtonian focus, (c) Cassegrain focus, and (d) Nasmyth/coudé focus. Each design uses a primary mirror at the bottom of the telescope to capture radiation, which is then directed along different paths for analysis. Notice that the secondary mirrors shown in (c) and (d) are actually slightly diverging, so that they move the focus outside the telescope.

    7. 5.1 Optical Telescopes Figure 5-7. (a) The two 10-m telescopes of the Keck Observatory. (b) Artist’s illustration of the telescope, the path taken by an incoming beam of starlight, and some of the locations where instruments may be placed. (c) One of the 10-m mirrors. (The odd shape is explained in Section 5.3.) Note the technician in orange coveralls at center. (W. M. Keck Observatory) Figure 5-7. (a) The two 10-m telescopes of the Keck Observatory. (b) Artist’s illustration of the telescope, the path taken by an incoming beam of starlight, and some of the locations where instruments may be placed. (c) One of the 10-m mirrors. (The odd shape is explained in Section 5.3.) Note the technician in orange coveralls at center. (W. M. Keck Observatory)

    8. Discovery 5-1: The Hubble Space Telescope

    9. Discovery 5-1: The Hubble Space Telescope

    10. Discovery 5-1: The Hubble Space Telescope

    11. 5.2 Telescope Size Figure 5-8. Effect of increasing telescope size on an image of the Andromeda galaxy. Both photographs had the same exposure time, but image (b) was taken with a telescope twice the size of that used to make image (a). Fainter detail can be seen as the diameter of the telescope mirror increases because larger telescopes are able to collect more photons per unit time. (Adapted from AURA) Figure 5-8. Effect of increasing telescope size on an image of the Andromeda galaxy. Both photographs had the same exposure time, but image (b) was taken with a telescope twice the size of that used to make image (a). Fainter detail can be seen as the diameter of the telescope mirror increases because larger telescopes are able to collect more photons per unit time. (Adapted from AURA)

    12. 5.2 Telescope Size Figure 5-11. Two comparably bright light sources become progressively clearer when viewed at finer and finer angular resolution. When the angular resolution is much poorer than the separation of the objects, as in (a), the objects appear as a single fuzzy “blob.” As the resolution improves, through (b) and (c), the two sources become discernible as separate objects. Figure 5-11. Two comparably bright light sources become progressively clearer when viewed at finer and finer angular resolution. When the angular resolution is much poorer than the separation of the objects, as in (a), the objects appear as a single fuzzy “blob.” As the resolution improves, through (b) and (c), the two sources become discernible as separate objects.

    13. 5.2 Telescope Size Figure 5-12. Detail becomes clearer in the Andromeda galaxy as the angular resolution is improved some 600 times, from (a) 10’, to (b) 1’, (c) 5”, and (d) 1”. (Adapted from AURA) Figure 5-12. Detail becomes clearer in the Andromeda galaxy as the angular resolution is improved some 600 times, from (a) 10’, to (b) 1’, (c) 5”, and (d) 1”. (Adapted from AURA)

    14. 5.3 Images and Detectors Figure 5-13. CCD Chip A charge-coupled device (CCD) consists of hundreds of thousands, or even millions, of tiny light-sensitive cells called pixels, usually arranged in a square array. Light striking a pixel causes an electrical charge to build up on it. By electronically reading out the charge on each pixel, a computer can reconstruct the pattern of light—the image— falling on the chip. (a) Detail of a CCD array. (b) A CCD chip mounted for use at the focus of a telescope. (c) Typical data from the chip consist of an array of numbers, running from 0 to 9 in this simplified example. Each number represents the intensity of the radiation striking that particular pixel. (d) When interpreted as intensity levels on a computer screen, an image of the field of view results. (MIT Lincoln Lab) Figure 5-13. CCD Chip A charge-coupled device (CCD) consists of hundreds of thousands, or even millions, of tiny light-sensitive cells called pixels, usually arranged in a square array. Light striking a pixel causes an electrical charge to build up on it. By electronically reading out the charge on each pixel, a computer can reconstruct the pattern of light—the image— falling on the chip. (a) Detail of a CCD array. (b) A CCD chip mounted for use at the focus of a telescope. (c) Typical data from the chip consist of an array of numbers, running from 0 to 9 in this simplified example. Each number represents the intensity of the radiation striking that particular pixel. (d) When interpreted as intensity levels on a computer screen, an image of the field of view results. (MIT Lincoln Lab)

    15. 5.3 Images and Detectors Figure 5-14. Image Processing (a) Ground-based view of the star cluster R136, a group of stars in the Large Magellanic Cloud (a nearby galaxy). (b) The “raw” image of this same region as seen by the Hubble Space Telescope in 1990, before its first repair mission. (c) The same image after computer processing that partly compensated for imperfections in the mirror. (d) The same region as seen by the repaired HST in 1994, here observed at a somewhat bluer wavelength. (AURA/NASA) Figure 5-14. Image Processing (a) Ground-based view of the star cluster R136, a group of stars in the Large Magellanic Cloud (a nearby galaxy). (b) The “raw” image of this same region as seen by the Hubble Space Telescope in 1990, before its first repair mission. (c) The same image after computer processing that partly compensated for imperfections in the mirror. (d) The same region as seen by the repaired HST in 1994, here observed at a somewhat bluer wavelength. (AURA/NASA)

    16. 5.4 High-Resolution Astronomy Figure 5-15. Light rays from a distant star strike a telescope detector at slightly different locations because of turbulence in Earth’s atmosphere. Over time, the light covers a roughly circular region on the detector, and even the pointlike image of a star is recorded as a small disk, called the seeing disk. Figure 5-15. Light rays from a distant star strike a telescope detector at slightly different locations because of turbulence in Earth’s atmosphere. Over time, the light covers a roughly circular region on the detector, and even the pointlike image of a star is recorded as a small disk, called the seeing disk.

    17. 5.4 High-Resolution Astronomy Figure 5-16. European Southern Observatory Located in the Andes Mountains of Chile, the European Southern Observatory at La Silla is run by a consortium of European nations. Numerous domes house optical telescopes of different sizes, each with varied support equipment, making this one of the most versatile observatories south of the equator. The largest telescope at La Silla—the square building to the right of center—is the New Technology Telescope, a 3.5-m state-of-the-art active optics device. (ESO) Figure 5-16. European Southern Observatory Located in the Andes Mountains of Chile, the European Southern Observatory at La Silla is run by a consortium of European nations. Numerous domes house optical telescopes of different sizes, each with varied support equipment, making this one of the most versatile observatories south of the equator. The largest telescope at La Silla—the square building to the right of center—is the New Technology Telescope, a 3.5-m state-of-the-art active optics device. (ESO)

    18. 5.4 High-Resolution Astronomy Figure 5-17. Active Optics These false-color infrared photographs of part of the star cluster R136—the same object shown in Figure 5.14—contrast the resolution obtained (a) without and (b) with an active optics system. Both images were taken with the New Technology Telescope shown in Figure 5.16. (ESO) Figure 5-17. Active Optics These false-color infrared photographs of part of the star cluster R136—the same object shown in Figure 5.14—contrast the resolution obtained (a) without and (b) with an active optics system. Both images were taken with the New Technology Telescope shown in Figure 5.16. (ESO)

    19. 5.4 High-Resolution Astronomy Figure 5-18. Adaptive-Optics System In this daytime photo, a test is being conducted at the Lick Observatory 3-m Shane telescope in California. A laser is used to create an “artificial star” (light reflected from the atmosphere back into the telescope) to improve guiding. The laser beam probes the atmosphere above the telescope, allowing tiny computer-controlled changes to be made in the shape of the mirror surface thousands of times each second. (Lick Observatory) Figure 5-18. Adaptive-Optics System In this daytime photo, a test is being conducted at the Lick Observatory 3-m Shane telescope in California. A laser is used to create an “artificial star” (light reflected from the atmosphere back into the telescope) to improve guiding. The laser beam probes the atmosphere above the telescope, allowing tiny computer-controlled changes to be made in the shape of the mirror surface thousands of times each second. (Lick Observatory)

    20. 5.4 High-Resolution Astronomy Figure 5-19. Adaptive Optics in Action (a) The improvement in image quality produced by adaptive optics systems can be seen in these images acquired by the 8-m Gemini telescope atop Mauna Kea in Hawaii. The uncorrected visible-light image (left) of the star cluster NGC 6934 is resolved to a little less than 1”. With adaptive optics applied (right), the resolution in the infrared is improved by nearly a factor of 10, allowing more stars to be seen more clearly. (b) These visible-light images were acquired at a military observatory atop Mount Haleakala in Maui, Hawaii. The uncorrected image (left) of the double star Castor is a blur spread over several arc seconds, giving only a hint of its binary nature. With adaptive compensation applied (right), the resolution is improved to a mere 0.1”, and the two stars are clearly separated. (NOAO; MIT Lincoln Laboratory) Figure 5-19. Adaptive Optics in Action (a) The improvement in image quality produced by adaptive optics systems can be seen in these images acquired by the 8-m Gemini telescope atop Mauna Kea in Hawaii. The uncorrected visible-light image (left) of the star cluster NGC 6934 is resolved to a little less than 1”. With adaptive optics applied (right), the resolution in the infrared is improved by nearly a factor of 10, allowing more stars to be seen more clearly. (b) These visible-light images were acquired at a military observatory atop Mount Haleakala in Maui, Hawaii. The uncorrected image (left) of the double star Castor is a blur spread over several arc seconds, giving only a hint of its binary nature. With adaptive compensation applied (right), the resolution is improved to a mere 0.1”, and the two stars are clearly separated. (NOAO; MIT Lincoln Laboratory)

    21. 5.5 Radio Astronomy Figure 5-20. Radio Telescope (a) The 105-m-diameter device at the National Radio Astronomy Observatory in Green Bank, West Virginia, is 150 m tall—taller than the Statue of Liberty and nearly as tall as the Washington Monument. (b) Schematic diagram of the telescope, showing the path taken by an incoming beam of radio radiation. (NRAO) Figure 5-20. Radio Telescope (a) The 105-m-diameter device at the National Radio Astronomy Observatory in Green Bank, West Virginia, is 150 m tall—taller than the Statue of Liberty and nearly as tall as the Washington Monument. (b) Schematic diagram of the telescope, showing the path taken by an incoming beam of radio radiation. (NRAO)

    22. 5.5 Radio Astronomy Figure 5-21. Arecibo Observatory An aerial photograph of the 300-m-diameter dish at the National Astronomy and Ionospheric Center near Arecibo, Puerto Rico. The receivers that detect the focused radiation are suspended nearly 150 m (about 45 stories) above the center of the dish. The left inset shows a close-up of the radio receivers hanging high above the dish. The right inset shows technicians adjusting the dish surface to make it smoother. (D. Parker/T. Acevedo/NAIC; Cornell) Figure 5-21. Arecibo Observatory An aerial photograph of the 300-m-diameter dish at the National Astronomy and Ionospheric Center near Arecibo, Puerto Rico. The receivers that detect the focused radiation are suspended nearly 150 m (about 45 stories) above the center of the dish. The left inset shows a close-up of the radio receivers hanging high above the dish. The right inset shows technicians adjusting the dish surface to make it smoother. (D. Parker/T. Acevedo/NAIC; Cornell)

    23. 5.5 Radio Astronomy Figure 5-23. Orion Nebula in Radio and Visible The Orion Nebula is a star-forming region about 1500 light-years from Earth. (The nebula is located in the constellation Orion and can be seen in Figure 1.8.) The bright regions in this photograph are stars and clouds of glowing gas. The dark regions are not empty, but their visible emission is obscured by interstellar matter. Superimposed on the optical image is a radio contour map (blue lines) of the same region. Each curve of the contour map represents a different intensity of radio emission. The resolution of the optical image is about 1”; that of the radio map is 1’. (Background photo: AURA) Figure 5-23. Orion Nebula in Radio and Visible The Orion Nebula is a star-forming region about 1500 light-years from Earth. (The nebula is located in the constellation Orion and can be seen in Figure 1.8.) The bright regions in this photograph are stars and clouds of glowing gas. The dark regions are not empty, but their visible emission is obscured by interstellar matter. Superimposed on the optical image is a radio contour map (blue lines) of the same region. Each curve of the contour map represents a different intensity of radio emission. The resolution of the optical image is about 1”; that of the radio map is 1’. (Background photo: AURA)

    24. 5.6 Interferometry Figure 5-24. VLA Interferometer (a) This large interferometer, located on the Plain of San Augustin in New Mexico, comprises 27 separate dishes spread along a Y-shaped pattern about 30 km across. The most sensitive radio device in the world, it is called the Very Large Array, or VLA for short. (b) A close-up view from ground level shows how some of the VLA dishes are mounted on railroad tracks so that they can be repositioned easily. (NRAO) Figure 5-24. VLA Interferometer (a) This large interferometer, located on the Plain of San Augustin in New Mexico, comprises 27 separate dishes spread along a Y-shaped pattern about 30 km across. The most sensitive radio device in the world, it is called the Very Large Array, or VLA for short. (b) A close-up view from ground level shows how some of the VLA dishes are mounted on railroad tracks so that they can be repositioned easily. (NRAO)

    25. 5.6 Interferometry Figure 5-25. Interferometry Two detectors, A and B, record different signals from the same incoming wave because of the time it takes the radiation to traverse the distance between them. When the signals are combined, the amount of interference depends on the wave’s direction of motion, providing a means of measuring the position of the source in the sky. Here, the dark-blue waves come from a source high in the sky and interfere destructively when captured by antennas A and B. But when the same source has moved because of Earth’s rotation (light-blue waves), the interference can be constructive. Figure 5-25. Interferometry Two detectors, A and B, record different signals from the same incoming wave because of the time it takes the radiation to traverse the distance between them. When the signals are combined, the amount of interference depends on the wave’s direction of motion, providing a means of measuring the position of the source in the sky. Here, the dark-blue waves come from a source high in the sky and interfere destructively when captured by antennas A and B. But when the same source has moved because of Earth’s rotation (light-blue waves), the interference can be constructive.

    26. 5.6 Interferometry Figure 5-26. Radio–Optical Comparison (a) VLA radio “image” (or radiograph) of the spiral galaxy M51, observed at radio frequencies with an angular resolution of a few arc seconds. (b) Visible-light photograph of that same galaxy, made with the 4-m Kitt Peak optical telescope and displayed on the same scale as (a). (NRAO/AURA) Figure 5-26. Radio–Optical Comparison (a) VLA radio “image” (or radiograph) of the spiral galaxy M51, observed at radio frequencies with an angular resolution of a few arc seconds. (b) Visible-light photograph of that same galaxy, made with the 4-m Kitt Peak optical telescope and displayed on the same scale as (a). (NRAO/AURA)

    27. 5.7 Space-Based Astronomy Figure 5-28. Smog Revealed An optical photograph (a) taken near San Jose, California, and an infrared photo (b) of the same area taken at the same time. Infrared radiation of long wavelength can penetrate smog much better than short-wavelength visible light. The same advantage pertains to astronomical observations: An optical view (c) of an especially dusty part of the central region of the Orion Nebula is more clearly revealed in this infrared image (d) showing a cluster of stars behind the obscuring dust. (Lick Observatory; NASA) Figure 5-28. Smog Revealed An optical photograph (a) taken near San Jose, California, and an infrared photo (b) of the same area taken at the same time. Infrared radiation of long wavelength can penetrate smog much better than short-wavelength visible light. The same advantage pertains to astronomical observations: An optical view (c) of an especially dusty part of the central region of the Orion Nebula is more clearly revealed in this infrared image (d) showing a cluster of stars behind the obscuring dust. (Lick Observatory; NASA)

    28. 5.7 Space-Based Astronomy Figure 5-29. Infrared Image (a) This infrared image of the Orion region was made by the Infrared Astronomy Satellite. In this false-color image, colors denote different temperatures, descending from white to orange to black. The resolution is about 1’. (b) The same region photographed in visible light with 1” resolution. The labels a and ß refer, respectively, to Betelgeuse and Rigel, the two brightest stars in the constellation. Note how the red star Betelgeuse is easily seen in the infrared (part a), whereas the blue star Rigel is very faint. (NASA; J. Sanford) Figure 5-29. Infrared Image (a) This infrared image of the Orion region was made by the Infrared Astronomy Satellite. In this false-color image, colors denote different temperatures, descending from white to orange to black. The resolution is about 1’. (b) The same region photographed in visible light with 1” resolution. The labels a and ß refer, respectively, to Betelgeuse and Rigel, the two brightest stars in the constellation. Note how the red star Betelgeuse is easily seen in the infrared (part a), whereas the blue star Rigel is very faint. (NASA; J. Sanford)

    29. 5.7 Space-Based Astronomy Figure 5-30. Spitzer Images Sample images from the Spitzer Space Telescope, now in orbit around the Sun, clearly show its camera’s capabilities. (a) The magnificent spiral galaxy, M81, about 12 million light-years away. (b) Its companion, M82, is not so serene, rather resembling a “smoking hot cigar.” ( JPL) Figure 5-30. Spitzer Images Sample images from the Spitzer Space Telescope, now in orbit around the Sun, clearly show its camera’s capabilities. (a) The magnificent spiral galaxy, M81, about 12 million light-years away. (b) Its companion, M82, is not so serene, rather resembling a “smoking hot cigar.” ( JPL)

    30. 5.7 Space-Based Astronomy Figure 5-31. Ultraviolet Images (a) A camera on board the Extreme Ultraviolet Explorer satellite captured this image of the Cygnus loop supernova remnant, the result of a massive star that blew itself virtually to smithereens. The release of energy was enormous and the afterglow has lingered for centuries. The glowing field of debris shown here within the telescope’s circular field of view lies some 1500 light-years from Earth. Based on the velocity of the outflowing debris, astronomers estimate that the explosion itself must have occurred about 12,000 years ago. (b) This false-color image of the spiral galaxy M81 and its companion M82, (see also Figure 5.30) made by the Galaxy Evolution Explorer satellite, reveals stars forming in the blue arms well away from the galaxy’s center. (NASA; GALEX) Figure 5-31. Ultraviolet Images (a) A camera on board the Extreme Ultraviolet Explorer satellite captured this image of the Cygnus loop supernova remnant, the result of a massive star that blew itself virtually to smithereens. The release of energy was enormous and the afterglow has lingered for centuries. The glowing field of debris shown here within the telescope’s circular field of view lies some 1500 light-years from Earth. Based on the velocity of the outflowing debris, astronomers estimate that the explosion itself must have occurred about 12,000 years ago. (b) This false-color image of the spiral galaxy M81 and its companion M82, (see also Figure 5.30) made by the Galaxy Evolution Explorer satellite, reveals stars forming in the blue arms well away from the galaxy’s center. (NASA; GALEX)

    31. 5.7 Space-Based Astronomy Figure 5-32. X-Ray Telescope (a) The arrangement of nested mirrors in an X-ray telescope allows the rays to be reflected at grazing angles and focused to form an image. (b) A cutaway 3-D rendition of the mirrors, showing their shape more clearly. Figure 5-32. X-Ray Telescope (a) The arrangement of nested mirrors in an X-ray telescope allows the rays to be reflected at grazing angles and focused to form an image. (b) A cutaway 3-D rendition of the mirrors, showing their shape more clearly.

    32. 5.7 Space-Based Astronomy Figure 5-34. X-Ray Image A false-color Chandra X-ray image of the supernova remnant Cassiopeia A, a debris field of scattered, hot gases that were once part of a massive star. Here, color represents the intensity of the X rays observed, from white (brightest) through red (faintest). Roughly 10,000 light-years from Earth and barely visible in the optical part of the spectrum, Cas A is now awash in brilliantly glowing X rays spread across some 10 light-years. (NASA) Figure 5-34. X-Ray Image A false-color Chandra X-ray image of the supernova remnant Cassiopeia A, a debris field of scattered, hot gases that were once part of a massive star. Here, color represents the intensity of the X rays observed, from white (brightest) through red (faintest). Roughly 10,000 light-years from Earth and barely visible in the optical part of the spectrum, Cas A is now awash in brilliantly glowing X rays spread across some 10 light-years. (NASA)

    33. 5.7 Space-Based Astronomy Figure 5-35. Gamma-Ray Astronomy (a) This photograph of the 17-ton Compton Gamma-Ray Observatory (CGRO; named after an American pioneer in gamma-ray telescopy) was taken by an astronaut during the satellite’s deployment from the space shuttle Atlantis over the Pacific Coast of the United States. (b) A typical false-color gamma-ray image—this one showing a violent event in the distant galaxy 3C279, also known as a “gamma-ray blazar.” (NASA) Figure 5-35. Gamma-Ray Astronomy (a) This photograph of the 17-ton Compton Gamma-Ray Observatory (CGRO; named after an American pioneer in gamma-ray telescopy) was taken by an astronaut during the satellite’s deployment from the space shuttle Atlantis over the Pacific Coast of the United States. (b) A typical false-color gamma-ray image—this one showing a violent event in the distant galaxy 3C279, also known as a “gamma-ray blazar.” (NASA)

    34. 5.8 Full-Spectrum Coverage Figure 5-36. Multiple Wavelengths The Milky Way Galaxy as it appears at (a) radio, (b) infrared, (c) visible, (d) X-ray, and (e) gamma-ray wavelengths. Each frame is a panoramic view covering the entire sky. The center of our Galaxy, which lies in the direction of the constellation Sagittarius, is at the center of each map. (NRAO; NASA; Lund Observatory; MPI; NASA) Figure 5-36. Multiple Wavelengths The Milky Way Galaxy as it appears at (a) radio, (b) infrared, (c) visible, (d) X-ray, and (e) gamma-ray wavelengths. Each frame is a panoramic view covering the entire sky. The center of our Galaxy, which lies in the direction of the constellation Sagittarius, is at the center of each map. (NRAO; NASA; Lund Observatory; MPI; NASA)

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