Great Observatories
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What are the Great Observatories?
The Great Observatories are a group of four U.S. satellite observatories with separate origins: the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Developed in the mid-1980s by Charles Pellerin, the Great Observatories concept aimed to provide an umbrella for large, expensive astrophysics missions that would span the electromagnetic spectrum and offer a comprehensive view of the universe.
Each observatory is named for an American astrophysicist: Edwin Hubble, Arthur H. Compton, Subrahmanyan Chandrasekhar, and Lyman Spitzer. Though linked conceptually, the missions had different origins and technologies. They often coordinated observing campaigns, but their observing programs were not consolidated.
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Why did the United States launch space-based observatories?
The United States launched space-based observatories to overcome limitations imposed by Earth's atmosphere, which absorbs parts of the electromagnetic spectrum and causes atmospheric turbulence. By placing instruments in space, astronomers can observe the universe in all regions of the spectrum, including gamma-ray, X-ray, ultraviolet, visible, and infrared regions. These satellite observatories avoid atmospheric distortion, gather data unachievable from the ground, and study cosmic phenomena. The Hubble Space Telescope, Compton Gamma Ray Observatory, Chandra X-Ray Observatory, and Spitzer Space Telescope are examples of these long-duration orbital facilities. These observatories have significantly contributed to understanding the universe's origin, evolution, and future.
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What are the names of the four main Great Observatories?
The four Great Observatories are U.S. satellite observatories launched by NASA. They include:
* Hubble Space Telescope
* Compton Gamma Ray Observatory
* Chandra X-ray Observatory
* Spitzer Space TelescopeThese observatories were designed to provide spatial and temporal coverage across the electromagnetic spectrum, ranging from gamma rays to infrared.
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How does each observatory study the universe differently?
The Great Observatories program includes four U.S. satellite observatories that study the universe across the electromagnetic spectrum. Each focuses on a different range, providing a comprehensive view.
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The Hubble Space Telescope captures visible, ultraviolet, and infrared light, offering high-resolution images and data on the chemical composition of cosmic objects.
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The Compton Gamma Ray Observatory mapped celestial gamma-ray sources, using techniques that narrowed the field of view to produce sharper views.
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The Chandra X-ray Observatory makes high-resolution images of celestial X-ray sources, focusing on black holes, supernova remnants, and distant objects.
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The Spitzer Space Telescope studies the cosmos at infrared wavelengths, detecting infrared radiation from extrasolar planets and distant galaxies.
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What important discoveries have the Great Observatories made?
The Great Observatories, a group of four U.S. satellite observatories, have made significant discoveries by providing unprecedented coverage across the electromagnetic spectrum.
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The Hubble Space Telescope determined the age of the universe to be about 13 to 14 billion years. It also played a key role in the discovery of dark energy and has shown scientists galaxies in early stages of growth, helping them understand how galaxies form.
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The Compton Gamma Ray Observatory mapped thousands of celestial gamma-ray sources and showed that mysterious bursts are distributed across the sky, implying that their sources are at the distant reaches of the universe.
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The Chandra X-ray Observatory found that starburst galaxies have a proportionally higher number of intermediate-size black holes. It also confirmed the presence of a supermassive black hole at the center of the Milky Way Galaxy and found direct proof of the existence of dark matter in the merging of two galaxy clusters.
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The Spitzer Space Telescope determined the temperature, atmospheric structure, composition, and dynamics of several extrasolar planets. It also detected infrared radiation from sources so far away that it looked almost 13 billion years back in time.
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How have the Great Observatories changed our understanding of space?
The Great Observatories, consisting of the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope, have broadened our view of the universe by providing spatial and temporal coverage across the electromagnetic spectrum.
These observatories have led to key discoveries such as determining the age of the universe, the discovery of dark energy, the observation of galaxies in early stages of development, and the detection of protoplanetary disks. The Chandra X-ray Observatory found evidence that supermassive black holes were more active in the past and confirmed a supermassive black hole at the center of the Milky Way. The Spitzer Space Telescope detected extrasolar planets and observed light from when the universe was less than a billion years old. The Compton Gamma Ray Observatory mapped thousands of gamma-ray sources and determined that gamma-ray bursts come from distant galaxies.
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Great Observatories, a semiformal grouping of four U.S. satellite observatories that had separate origins: the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. The grouping came about because the four would provide unprecedented spatial and temporal coverage across much of the electromagnetic spectrum from gamma rays (Compton) through X-rays (Chandra) and visible light (Hubble) to the infrared (Spitzer).
The Great Observatories concept was developed in the mid-1980s by American engineer Charles Pellerin, then Director of Astrophysics at the National Aeronautics and Space Administration (NASA), as a way of providing an umbrella for four large, expensive astrophysics missions that otherwise might be viewed as funding competitors. The idea was that by spanning the electromagnetic spectrum, the four would offer a comprehensive view of the universe that would help unify heretofore diverse perceptions. Comparisons were made between hearing an entire symphony rather than a solo instrument. In 1985 NASA introduced the program to the public in a full-colour booklet, The Great Observatories for Space Astrophysics, which was written by American astronomer Martin Harwit and American science writer Valerie Neal.
While linked conceptually, the four missions had vastly different origins and histories and shared little in the way of technology. Although they often joined in coordinated observing campaigns, no effort was made to consolidate their observing programs. Indeed, Spitzer was launched three years after Compton’s mission ended. Furthermore, the four were not identical in their ability to observe the heavens. Spitzer’s 0.85-metre (2.79-foot) primary mirror is about one-third the size of Hubble’s 2.4-metre (7.9-foot) primary and observes at much longer wavelengths than Hubble. Spitzer’s angular resolution is thus much coarser than Hubble’s. Because gamma rays have the shortest wavelength of all, they cannot be focused by mirrors or lenses in the same way as longer wavelength light. Therefore, Compton’s instruments used collimators and other techniques that narrowed the field of view and thus produced images coarser than those of the other three Great Observatories. Nevertheless, the four provided much sharper views of the universe than had been available previously. (Radio was not included in the Great Observatories. The long wavelength of radio waves required much larger satellites than were possible at that time, and most radio wavelengths can be detected from the ground.)
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As befitted the “Great” aspect of the program, the four spacecraft (listed here in order of launch) were named for American astrophysicists who made landmark contributions in their fields:
- Hubble Space Telescope, named for Edwin Hubble, who discovered the expansion of the universe. It was launched on April 24, 1990, and is planned to operate until 2013.
- Compton Gamma Ray Observatory, named for Arthur H. Compton, a pioneer in gamma-ray studies. It was launched on April 5, 1991, and was deorbited on June 4, 2000.
- Chandra X-ray Observatory, named for Subrahmanyan Chandrasekhar, who defined the upper mass limit for a white dwarf star. It was launched on July 23, 1999.
- Spitzer Space Telescope, named for Lyman Spitzer, who proposed the concept of orbiting observatories in 1946 and campaigned for such a mission from the 1950s through the ’70s. It was launched on Aug. 25, 2003, and is planned to operate until 2014.
The success of the Great Observatories has led NASA to outline a pair of Beyond Einstein Great Observatories: the International X-ray Observatory, designed to observe X-rays in finer detail than Chandra, and the Laser Interferometer Space Antenna (LISA), designed to seek gravity waves. However, NASA canceled development of these two observatories in 2011.