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[shadow=blue]How Hubble Space Telescope Works[/shadow]
Посмотреть вложение 3
Have you ever stared at the night sky and wondered what the universe looks like up close? Most of us are forced to stargaze with just our eyes, searching for pinpricks of light in the vast black night. Even if you're lucky enough to have access to a ground-based telescope, whose clarity depends on atmospheric factors such as clouds and weather, it still doesn't offer the kind of lucidity these stunning celestial objects deserve.
In 1946, an astrophysicist named Dr. Lyman Spitzer Jr. proposed that a telescope in space would reveal much clearer images of distant objects than any ground-based telescope. That sounds logical, right? But this was an outrageous idea, considering no one had even launched a rocket into outer space yet.
As the U.S. space program matured in the 1960s and 1970s, Spitzer lobbied NASA and Congress to develop a space telescope. In 1975, the European Space Agency (ESA) and NASA began drafting the initial plans for it, and in 1977, Congress approved the necessary funds. NASA named Lockheed Missiles (now Lockheed Martin) as the contractor that would build the telescope and its supporting systems, as well as assemble and test it.
The famous telescope was named after U.S. astronomer Edwin Hubble, whose observations of variable stars in distant galaxies confirmed that the universe was expanding and gave support to the Big Bang theory.
After a long delay due to the Challenger disaster in 1986, the Hubble Space Telescope shot into orbit on April 24, 1990, piggybacking aboard the Discovery space shuttle. Since its launch, Hubble has reshaped our view of space, with scientists writing thousands of papers based on the telescope's clear-eyed findings on important stuff like the age of the universe, gigantic black holes or what stars look like in the throes of death.
In this article, we'll talk about how Hubble has documented outer space and the instruments that have allowed it to do so. We'll also talk about a few of the problems the venerable telescope/spacecraft has encountered along the way.
Посмотреть вложение 2
[shadow=blue]COSTAR Saves the Day.[/shadow]
Almost immediately after it was deployed in 1990, astronomers discovered a problem with their beloved $1.5 billion, 43.5-ft (13.3-m) telescope. Their new tractor-trailer-sized eye in the sky couldn't focus properly. They realized that the telescope's primary mirror had been ground to the wrong dimension. Although the defect in the mirror -- roughly equal to one-fiftieth the thickness of a human hair -- would seem ridiculously minute to most of us, it caused the Hubble Space Telescope to suffer spherical aberration and produce fuzzy images. Surely the astronomers didn't spend years working on the telescope only to be satisfied with unremarkable snapshots of outer space.
Scientists came up with a replacement "contact" lens called COSTAR (Corrective Optics Space Telescope Axial Replacement) to repair the defect in the HST. COSTAR consisted of several small mirrors that would intercept the beam from the flawed mirror, fix the defect and relay the corrected beam to the scientific instruments at the focus of the mirror.
NASA astronauts and staff spent 11 months preparing for what would be one of the most challenging space missions ever attempted. Finally, in December 1993, seven men aboard the space shuttle Endeavour rocketed into space for the HST's first servicing mission.
It took the crew one week to make all of the necessary repairs, and when the telescope was tested after the servicing mission, the images were vastly improved. Today, all of the instruments placed in the HST have built-in corrective optics for the mirror's defect, and COSTAR is no longer needed.
There's more to Hubble than COSTAR, though, and we'll talk about some of those critical parts next.
Посмотреть вложение 1
[shadow=blue]Anatomy of the HST[/shadow]
Like any telescope, the HST has a long tube that is open at one end to let in light. It has mirrors to gather and bring the light to a focus where its "eyes" are located. The HST has several types of "eyes" in the form of various instruments. Just as insects can see ultraviolet light or we humans can see visible light, Hubble must also be able to see the various types of light raining down from the heavens.
Specifically, Hubble is a Cassegrain reflector telescope. That just means that light enters the device through the opening and bounces off the primary mirror to a secondary mirror. The secondary mirror in turn reflects the light through a hole in the center of the primary mirror to a focal point behind the primary mirror. If you drew the path of the incoming light, it would like the letter "W," except with three downward humps instead of two.
At the focal point, smaller, half-reflective, half-transparent mirrors distribute the incoming light to the various scientific instruments. (We'll talk more about those instruments in the next section.) As you might have guessed, these aren't just ordinary mirrors that you might gaze in to admire your reflection.
HST's mirrors are made of glass and coated with layers of pure aluminum (three-millionths of an inch thick) and magnesium fluoride (one-millionth of an inch thick) to make them reflect visible, infrared and ultraviolet light. The primary mirror is 7.9 feet (2.4 meters) in diameter, and the secondary mirror is 1.0 feet (0.3 meters) in diameter.
Next we'll talk about what Hubble does with all that light after it hits the telescope's mirrors.
[dropshadow=blue]Hubble's Scientific Instruments: WFPC2, NICMOS and STIS[/dropshadow]
By looking at the different wavelengths, or the spectrum of light, of a celestial object, you can discern many of its properties. To do this, HST is equipped with several scientific instruments. Each instrument uses charge-coupled devices (CCDs) rather than photographic film to capture the light. The light detected by the CCDs are turned into digital signals, which are stored in onboard computers and relayed to Earth. The digital data are then transformed into amazing photos. Let's look at how each instrument contributes to those images.
The Wide Field and Planetary Camera 2 (WFPC2) is Hubble's main "eye," or camera. It sees with the help of four CCD chips arranged in an "L" shape to catch the light -- three low-resolution, wide-field CCD chips, plus one high-resolution planetary camera CCD chip. All four chips are exposed simultaneously to the target, and the target image is centered on the desired CCD chip. This eye can see visible and ultraviolet light, and can take images through various filters to make natural color pictures, such as this well-known image of the Eagle nebula.
Often, interstellar gas and dust can block our vision of the visible light from various celestial objects. No problem: Hubble can see the infrared light, or heat, from the objects hidden in the dust and gas. To see this infrared light, HST has three sensitive cameras that make up the Near Infrared Camera and Multi-object Spectrometer (NICMOS).
Besides illuminating a celestial object, the light emanating from that object can also reveal what it's made of. The specific colors tell us what elements are present, and the intensity of each color tells us how much of that element is present. The Space Telescope Imaging Spectrograph (STIS) separates the incoming colors of light much as a prism makes a rainbow.
In addition to describing the chemical composition, the spectrum can convey the temperature, density and motion of a celestial object. If the object is moving, the chemical fingerprint may shift toward the blue end (moving toward us) or the red end (moving away from us) of the spectrum. Unfortunately, the STIS lost power in 2004 and has been inactive ever since.
Keep reading to find out what other scientific instruments Hubble has up its telescopic sleeve.
Посмотреть вложение 3
Have you ever stared at the night sky and wondered what the universe looks like up close? Most of us are forced to stargaze with just our eyes, searching for pinpricks of light in the vast black night. Even if you're lucky enough to have access to a ground-based telescope, whose clarity depends on atmospheric factors such as clouds and weather, it still doesn't offer the kind of lucidity these stunning celestial objects deserve.
In 1946, an astrophysicist named Dr. Lyman Spitzer Jr. proposed that a telescope in space would reveal much clearer images of distant objects than any ground-based telescope. That sounds logical, right? But this was an outrageous idea, considering no one had even launched a rocket into outer space yet.
As the U.S. space program matured in the 1960s and 1970s, Spitzer lobbied NASA and Congress to develop a space telescope. In 1975, the European Space Agency (ESA) and NASA began drafting the initial plans for it, and in 1977, Congress approved the necessary funds. NASA named Lockheed Missiles (now Lockheed Martin) as the contractor that would build the telescope and its supporting systems, as well as assemble and test it.
The famous telescope was named after U.S. astronomer Edwin Hubble, whose observations of variable stars in distant galaxies confirmed that the universe was expanding and gave support to the Big Bang theory.
After a long delay due to the Challenger disaster in 1986, the Hubble Space Telescope shot into orbit on April 24, 1990, piggybacking aboard the Discovery space shuttle. Since its launch, Hubble has reshaped our view of space, with scientists writing thousands of papers based on the telescope's clear-eyed findings on important stuff like the age of the universe, gigantic black holes or what stars look like in the throes of death.
In this article, we'll talk about how Hubble has documented outer space and the instruments that have allowed it to do so. We'll also talk about a few of the problems the venerable telescope/spacecraft has encountered along the way.
Посмотреть вложение 2
[shadow=blue]COSTAR Saves the Day.[/shadow]
Almost immediately after it was deployed in 1990, astronomers discovered a problem with their beloved $1.5 billion, 43.5-ft (13.3-m) telescope. Their new tractor-trailer-sized eye in the sky couldn't focus properly. They realized that the telescope's primary mirror had been ground to the wrong dimension. Although the defect in the mirror -- roughly equal to one-fiftieth the thickness of a human hair -- would seem ridiculously minute to most of us, it caused the Hubble Space Telescope to suffer spherical aberration and produce fuzzy images. Surely the astronomers didn't spend years working on the telescope only to be satisfied with unremarkable snapshots of outer space.
Scientists came up with a replacement "contact" lens called COSTAR (Corrective Optics Space Telescope Axial Replacement) to repair the defect in the HST. COSTAR consisted of several small mirrors that would intercept the beam from the flawed mirror, fix the defect and relay the corrected beam to the scientific instruments at the focus of the mirror.
NASA astronauts and staff spent 11 months preparing for what would be one of the most challenging space missions ever attempted. Finally, in December 1993, seven men aboard the space shuttle Endeavour rocketed into space for the HST's first servicing mission.
It took the crew one week to make all of the necessary repairs, and when the telescope was tested after the servicing mission, the images were vastly improved. Today, all of the instruments placed in the HST have built-in corrective optics for the mirror's defect, and COSTAR is no longer needed.
There's more to Hubble than COSTAR, though, and we'll talk about some of those critical parts next.
Посмотреть вложение 1
[shadow=blue]Anatomy of the HST[/shadow]
Like any telescope, the HST has a long tube that is open at one end to let in light. It has mirrors to gather and bring the light to a focus where its "eyes" are located. The HST has several types of "eyes" in the form of various instruments. Just as insects can see ultraviolet light or we humans can see visible light, Hubble must also be able to see the various types of light raining down from the heavens.
Specifically, Hubble is a Cassegrain reflector telescope. That just means that light enters the device through the opening and bounces off the primary mirror to a secondary mirror. The secondary mirror in turn reflects the light through a hole in the center of the primary mirror to a focal point behind the primary mirror. If you drew the path of the incoming light, it would like the letter "W," except with three downward humps instead of two.
At the focal point, smaller, half-reflective, half-transparent mirrors distribute the incoming light to the various scientific instruments. (We'll talk more about those instruments in the next section.) As you might have guessed, these aren't just ordinary mirrors that you might gaze in to admire your reflection.
HST's mirrors are made of glass and coated with layers of pure aluminum (three-millionths of an inch thick) and magnesium fluoride (one-millionth of an inch thick) to make them reflect visible, infrared and ultraviolet light. The primary mirror is 7.9 feet (2.4 meters) in diameter, and the secondary mirror is 1.0 feet (0.3 meters) in diameter.
Next we'll talk about what Hubble does with all that light after it hits the telescope's mirrors.
[dropshadow=blue]Hubble's Scientific Instruments: WFPC2, NICMOS and STIS[/dropshadow]
By looking at the different wavelengths, or the spectrum of light, of a celestial object, you can discern many of its properties. To do this, HST is equipped with several scientific instruments. Each instrument uses charge-coupled devices (CCDs) rather than photographic film to capture the light. The light detected by the CCDs are turned into digital signals, which are stored in onboard computers and relayed to Earth. The digital data are then transformed into amazing photos. Let's look at how each instrument contributes to those images.
The Wide Field and Planetary Camera 2 (WFPC2) is Hubble's main "eye," or camera. It sees with the help of four CCD chips arranged in an "L" shape to catch the light -- three low-resolution, wide-field CCD chips, plus one high-resolution planetary camera CCD chip. All four chips are exposed simultaneously to the target, and the target image is centered on the desired CCD chip. This eye can see visible and ultraviolet light, and can take images through various filters to make natural color pictures, such as this well-known image of the Eagle nebula.
Often, interstellar gas and dust can block our vision of the visible light from various celestial objects. No problem: Hubble can see the infrared light, or heat, from the objects hidden in the dust and gas. To see this infrared light, HST has three sensitive cameras that make up the Near Infrared Camera and Multi-object Spectrometer (NICMOS).
Besides illuminating a celestial object, the light emanating from that object can also reveal what it's made of. The specific colors tell us what elements are present, and the intensity of each color tells us how much of that element is present. The Space Telescope Imaging Spectrograph (STIS) separates the incoming colors of light much as a prism makes a rainbow.
In addition to describing the chemical composition, the spectrum can convey the temperature, density and motion of a celestial object. If the object is moving, the chemical fingerprint may shift toward the blue end (moving toward us) or the red end (moving away from us) of the spectrum. Unfortunately, the STIS lost power in 2004 and has been inactive ever since.
Keep reading to find out what other scientific instruments Hubble has up its telescopic sleeve.