LESSON 7. RADIO TELESCOPE
1. Read the new words:
radio telescope
extraterrestrial
to emit , ,
photon ,
reflector , ,
wavelength
light wave
to focus , , ;
steerable paraboloid
to dub
pickup antenna
feed , () , ()
broad bandwidth
continuum ,
spectroscopic
radio spectrum
frequency range
time-consuming , ;
to restrict
frequency channel
radiometer , ;
weak source
radio emission
to amplify ,
performance ; ,
to limit , ,
to depart , ;
wind load
2. Read the text and translate it:
Radio telescope is an astronomical instrument which is used to detect radio-frequency radiation emitted by extraterrestrial sources.
Radio telescopes are much larger than optical telescopes because radio wavelengths are much longer than optical wavelengths. The longer wavelengths means that the radio waves have lower energy than optical light waves. In order to collect enough radio photons to detect a signal, the radio dishes must be very large. Both optical and radio telescope reflectors use a parabolic shape to perfectly focus the light to a point.
The first radio telescope, built in 1937 by Grote Reber of Wheaton, Ill., U.S., was a steerable paraboloid--i.e., a device with a parabolically shaped reflector, dubbed the "dish," that focuses the incoming radio waves onto a small pickup antenna, or "feed."
Radio telescopes are used to measure broad-bandwidth continuum radiation as well as spectroscopic features due to atomic and molecular lines found in the radio spectrum of astronomical objects. In early radio telescopes, spectroscopic observations were made by tuning a receiver across a sufficiently large frequency range to cover the various frequencies of interest. This procedure, however, was extremely time-consuming and greatly restricted observations. Modern radio telescopes observe simultaneously at a large number of frequencies by dividing the signals up into as many as several thousand separate frequency channels that may range over a total bandwidth of tens to hundreds of megahertz.
Radio telescopes vary widely, but they all have two basic components: a large radio antenna and a radiometer or radio receiver. The sensitivity of a radio telescope, i.e., the ability to measure weak sources of radio emission--depends on the area and efficiency of the antenna, the sensitivity of the radio receiver used to amplify and detect the signals, and the duration of the observation.
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The performance of a radio telescope is limited by various factors: the accuracy of a reflecting surface that may depart from the ideal shape because of manufacturing irregularities; the effect of wind load; thermal deformations that cause differential expansion and contraction; and deflections due to changes in gravitational forces as the antenna is pointed to different parts of the sky.
3. Answer the following questions:
1) Is the radio telescope used to detect radio-frequency radiation?
2) Are radio telescopes larger than optical telescopes?
How can you explain it?
3) When was the first radio telescope built?
4) What do you know about spectroscopic observations in early radio telescopes?
5) How do modern radio telescopes observe?
6) What are the basic components of a radio telescope?
7) What is the sensitivity of a radio telescope?
8) What factors do limit the performance of a radio telescope?
4. Correct the wrong statements:
Radio telescopes allow astronomers to observe radio waves which have much longer wavelengths than does visible light coming from space.
Radio telescopes are smaller than optical telescopes.
A radio telescope typically consists of a bowl-shaped antenna similar to a modern satellite dish.
The first radio telescope was built in 1973 by Grote Wheaton.
In early radio telescopes spectroscopic observations were energy efficient and time consuming.
The sensitivity of a radio telescope is the ability to restrict observations.
Thermal deformations cause differential expansion and make the antenna point to different parts of the sky.
