Image Processing Reference
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Figure3.8 Passive millimeter-wave camera on aircraft nose. (CourtesyofNorthrup
GrummanCorporation)
unknown origin coming from outer space. Karl Jansky was an American radio
engineer studying thunderstorm interference of radio transmissions. He noticed
that his experimental directional antenna (shown in Fig. 3.9) received signals in
the 14.6-m waveband—signals that could not be linked to any terrestrial radio
sources. The apparent position of the source was a point in the sky; this source
moved around in the sky and reached peak strength every 24 hours. This suggested
that the source's position was fixed with respect to the stars, rising and setting like
a star, which meant that it had to be extraterrestrial.
Today we know that this object is a powerful celestial radio source located at
the center of our galaxy. The object is located in the portion of the sky nearest the
constellation Sagittarius, and since it is the brightest radio source in Sagittarius,
it is known asSagittariusA. In fact, Sagittarius A is one of the most powerful
radio sources in the sky as seen from Earth. It is believed to be a massive
rotatingblackholethat generates intense radio waves through the interaction
of electric and magnetic fields with matter that is being sucked into the hole. 8
Radio astronomers have built on Jansky's pioneering work, creating large, highly
directionaldishantennasystems that can scan images of the sky in the radio band
of the electromagnetic spectrum. This technology has led to the discovery of many
unexpected types of celestial objects such aspulsars,quasars, and vastmolecular
clouds, all of which emit radio waves.
8 Ibid.
 
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