Category Science & Technology

In 1960, very strong radio emissions were observed by an American astronomer, Allan R. Sandage to be coming from certain localized direction in the sky. When viewed on the photographic plate, they appeared like stars. But they were not stars, as proved by their other characteristics including a large red shift. The accurate position measurement of these star like objects on optical photographs, led to the discovery of a new class of objects in the universe, the quasars (quasi-stellar sources).

They appear star like on the photograph because their angular diameters are less than about 1 second of an arc, which is the resolution limit of ground-based optical telescopes. Since stars also have angular diameters much less than this, they too appear unresolved or point-like on a photograph.

In 1962 a much brighter star like object 3C273 was identified by Maarten Schmidt with the help of a radio telescope in Australia. Its red shift was found to be 0.158. This red shift turned out to be far larger than any other that had been detected for ordinary galaxies. These observations established the existence of quasars beyond doubt.

Quasars are generally much bluer than most of the stars, except white dwarf stars. The blueness of quasars, as an identifying characteristic, led to the discovery that many blue star like objects have a large red shift, and are therefore quasars. Till today scientists have studied more than 1000 quasars but their nature and distance from earth remain a puzzle.

Quasars consist of a massive nucleus with a total size of less than a light year, which is surrounded by an extended halo of gas excited by the energy radiated by the central object. The central object emits radiation over a wide spectral range. Some quasars emit significant amount of energy at radio frequencies ranging from about 30 MHz to 100 GHz. It is believed that the energy emitted by quasars is gravitational and not thermonuclear in origin. More than ergs of energy are released in quasars over their life-time.

Till to day scientists have not been able to measure the exact distance of quasars from the earth. Various similarities of quasars with radio galaxies strongly suggest that quasars are also active nuclei of galaxies might be associated with the birth of some galaxies. Studies have shown that quasars must have been much more common in the universe about many years ago.

          The polaroid camera is also known as the ‘instant camera’ because it takes pictures and develops them in a matter of minutes. It was invented by Edwin H. Land of the United States and the first polaroid camera was sold in 1948. At that stage, it took only black and white photographs. Later, another camera was built that could take pictures and develop colour photographs.

          Polaroid cameras are loaded with a double picture roll. One part is a negative roll of the film, and the other a positive roll of a special printing paper. Small pods (containers) of chemicals are joined to the positive roll. After exposure to light through the camera’s lens, the negative and positive rolls are made to pass through a pair of rollers that break the chemical pods. The chemicals flow over the exposed portion of the negative roll and develop a negative image on the roll – the parts of the picture that should be black are white, and the parts that should be white are black. More chemical reactions take place between the pod chemicals and the chemicals coated on the positive roll, and a positive photograph is made – the white areas in the photograph are printed white and the black areas black. This process takes about 10 seconds for a black and white photograph and upto a minute for a colour one. 

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