Чтение общенаучной литературы. Кытманова О.А. - 46 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

47
The Start of Radio Astronomy in 1932 an American electrical engineer, Karl
Jansky, constructed the first radio telescope capable of picking up waves from the
Milky Way. The invention arose because in the previous year Jansky had found
that when he pointed an ordinary radio antenna towards the Milky Way he picked
up a faint hiss on his radio set. In the 1940s an English scientist, J. S. Hey, realized
that strange interference on radar equipment was in fact caused by radio waves
from the Sun. About this time, an American amateur astronomer, Grote Reber,
built the first true radio telescope with which he detected a strong source of radio
waves at ' he center of the Milky Way. From these small beginnings the giant radio
telescopes of the present day have evolved.
Radio Telescopes
A radio telescope has three essential components: something to reflect the cosmic
radio waves, a detector to pick them up, and a receiver for amplifying and
recording the signals, which are extremely feeble. The reflecting "mirror" can be
either an array, or set. of many antennas connected in a special way, or a metal
sheet or wire netting. It is not necessary for the reflector to be solid, and wire net-
mg reflects radio waves very well Nor does the "mirror"' need to be particularly
smooth, unless it is going to be used to receive signals it wavelengths smaller than
10 centimeters (4 inches).
Radio telescopes need to be far bigger than optical ones. This is mainly because
radio waves are about a million times longer in wavelength than those of visible
light, and for that reason alone large reflectors and arrays are needed in order to
make detailed maps of cosmic radio emission. A second reason for the size is that
the radio signals are extremely weak, and therefore undetectable unless a large
collecting area is used.
The detector is generally a simple dipole antenna or rod with a connecting wire
fixed to its middle . This is positioned at the focus of the dish-shaped telescope; its
protective housing includes an amplifier to boost the incoming signal, which is too
weak to be sent to the receiver. The radio receiver is complex and normally part of
a computer system The information collected by the telescope can he processed by
computer to make maps of the radio sky or to produce a "photograph"' of the radio
image. The receiving system may include a radio spectrometer which is capable of
recording the strength of the radio signal over a narrow range of wavelengths. This
particular technique can be used to identify, b} means of" characteristic radio
signals, the atoms and molecules in gas clouds in the Milky Way.
The largest single-dish radio telescope in the world is in the United States, at
Arecibo, in Puerto Rico. Here engineers have constructed a 300-meter (1,000-foot)
radio telescope by lining a natural crater with wire netting. The telescope cannot he
pointed just anywhere in the sky, but observers using it can move the detecting
dipole instead. In addition, the Earth spinning on its axis allows astronomers to
view different parts of the sky at different times of day.
More efficient than a fixed single-dish radio telescope like this is a steer able
instrument such as the one at Effelsberg. near Bonn, Germany. The dish of the
Effelsberg telescope is 100 meters (328 feet) across, making it the largest steer able
single-dish instrument in the world. Other steer able single-dish telescopes include

Страницы