VOA慢速英语: 哈勃空间望远镜25周年纪念
Before the Hubble Space Telescope, people saw the field of astronomydifferently than they do today. American spacecraft did provide detailedpictures of Jupiter and Saturn, planets in our own solar system. But deepspace, the place where nebulae and galaxies exist, remained mostlycolorless -- until the Hubble Space Telescope. It has provided detailed andoften colorful images of once unimaginable objects.
Friday marks 25 years since Hubble left the ground. It was launched on theAmerican space agency’s Space Shuttle Discovery. The agency, also knownas NASA, says the telescope can no longer be repaired in space. But a newspace telescope, the James Webb Space Telescope, is being built andtested. Plans call for it to be launched from French Guiana in October of 2018.
The Hubble and the Webb telescopes have much in common. Scientistsdesigned both to operate in the vacuum of outer space. In other words, theycan work in an environment without air. Both telescopes use mirrors tocollect and redirect light to make pictures, and radio signals to send theseimages back to earth. And both are powered by sunlight.
However, NASA officials say the James Webb Space Telescope is differentfrom Hubble. Matt Greenhouse is a project scientist for the Webb telescope.
“The Webb, as we call it, is the successor to Hubble Space Telescope, and it is designed to do science that the Hubble can’t do by virtue of its design. Oneof the biggest differences between the Webb and the Hubble is that the Webbis designed to be an infrared telescope to see these very primordial objects,these objects that are among the oldest objects in the universe.”
To examine these distant objects, Webb will not look at visible light – the lightwe see. Instead, it will look at infrared light, which is given off by hot objects.After its launch, the Webb telescope will enter an orbit 1.5 million kilometersabove earth’s atmosphere. That is much farther than Hubble’s orbit and willgive the Webb telescope a better ability to see infrared light, says Mr.Greenhouse.
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“With infrared radiation we can peer through clouds of dust in space thatobscure regions where stars are being born around us today.”
The Webb telescope’s mirror is also more than six times larger than Hubble’s. This means it will be able to create images with more detail and show objectsthat are father away and not as bright. The mirror is made of lightweightberyllium and covered with gold. The huge device comes in pieces so that itcan fit inside the Ariane 5 rocket that will carry the Webb telescope intospace.
Mr. Greenhouse says the instruments must be kept extremely cold so thatthey can observe infrared light.
“…more than minus 200 degree Celsius, which is what we call a cryogenictemperature. The reason for that is because anything above absolute zeroemits infrared light. If we didn’t cool the telescope, it would be blinded by itsown infrared emission.”
New technologies combined with the larger mirror mean that the Webbtelescope is more than 100 times more powerful than Hubble.
The Webb is being put together at the Goddard Space Flight Center inGreenbelt, Maryland. Matt Greenhouse says scientists are performing tests.They want to avoid the problems that the Hubble Space Telescope had whenit started.
Shortly after its launch on April 24th, 1990, NASA scientists found thatHubble’s mirror was too flat -- by about the width of a human hair. Not a lot, but enough to cause problems. Space shuttle astronauts repaired thetelescope in 1993. But this time, Matt Greenhouse says, mission scientistslearned from the experience.
“One of the big things that we learned from the Hubble is the Hubble didn’t dosomething called an end-to-end optical test, where we take the entireobservatory and shine light through it the way it will be done in space andmake sure everything works.”
That will be important because the Webb telescope is not designed to berepaired in space like Hubble.
Mr. Greenhouse says scientists are performing tests on the Webbtelescope’s optical systems. He hopes that the Webb will bring newdiscoveries as Hubble did before it.
Jennifer Wiseman is a senior project scientist with Hubble. She notes that itprovided new information about the birth and development of stars. She saysthe telescope showed that the universe is expanding and suggested the ageof the universe at 13.8 billion years. She says it also helped prove theexistence of black holes in some galaxies.
“Hubble was capable of looking at the fast motions of gas around the center ofanother galaxy and to discern that that fast motion, that fast rotation of gas,could only be held in place if there were something very massive in the core. It had to be a super massive black hole.”
After 25 years in space, Hubble not only remains in orbit but is working well.Astronomers hope that both telescopes can be operating at the same time sothey can work together.
Jennifer Wiseman says Hubble’s accomplishments are clear.
“I think that it causes at its best all of humanity to pause for a moment, look upand think about who we are and how we are all citizens of this onemagnificent planet in a very magnificent universe.”
The new Webb space telescope is an international project. NASA, theEuropean Space Agency and the Canadian Space Agency have workedtogether to build it at an estimated cost of over $8 billion dollars.
I’m Mario Ritter.
This story was based on from reports by VOA’s Rosanne Skirble. Mario Ritterwrote it for Learning English. George Grow was the editor.
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Words in This Story
nebula – n. a cloud of gas or dust in space that can be seen by reflected orradiated light
galaxies – n. any one of a very large group of stars that make up the universe
mirror – n. a piece of glass or similar material that reflects light
vacuum – n. empty space in which there is no air, gas or other matter
infrared light – n. light radiation that is not visible to the human eye and is at a longer wavelength than visible light, associated with heat
radiation – n. energy that comes from an object in the form of waves or rays
What do you think about the Hubble Space Telescope or the new JamesWebb Space Telescope? Let us know in the comment section below.
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