Progress on the nebulae in the early twentieth century was stim lated by the construction of large telescopes in good climates and the regular use of permanent records such as photographic plates and spectrograms. The Harvard telescope in Peru, the Crossley 1-m reflector at the Lick Observatory and the Mount Wilson 1.5-m played an important […]
Herschel’s discovery of stars embedded in nebulosity, the so-called planetary nebulae, reinforced a possible interpretation of the nebulae as planetary systems in the making. Such an interpretation correlated very well with the accepted theory of the origin of the Solar System developed by Pierre Simon de Laplace towards the end of the eighteenth century. According […]
The Draper catalogues provided astrophysicists with the massive numbers of spectra needed for statistical studies of the distribution of stellar types, which in turn might provide clues on stellar evolution. Two independent studies of particular interest, one by E.Hertzsprung, a Danish astronomer, the other by the American astronomer H.N.Russell, resulted in one of the corner-stones […]
In the mid-nineteenth century, very little was known about stars other than positions, apparent magnitudes, and, in a few cases distances. The method of determining distance, by trigonometrical parallax, was limited to those stars within a hundred parsecs of the Sun ; thus, even by 1890 fewer than 100 stars had known distances. Spectral analysis […]
Vital step were taken towards the detection of stellar parallax during the eighteenth century through the collection of extensive and precise stellar catalogues. In addition, more precise instruments, impossible for the crude technologies of earlier times, were being constructed. Both these factors contributed to many false alarms until the actual minuteness of stellar parallaxes was […]
Apart from the handful of remnants in our Galaxy which can be identified with particular explosive events, the ages of Supernova remnants must be determined by indirect means. In Some Cases, such as cas A, this may be; done by comparing the diameter of the remnant with its expansion velocity; in general, however, one must […]
X-rays have been detected from several supernova remnants by the use of satellite-borne telescopes. The case of the Crab Nebula has already been mentioned; here the X-rays are almost certainly due to synchrotron radiation. Most SNRs, however, do not contain a pulsar that can maintain the supply of the ultra-relativistic electrons which are necessary for […]
The CRAB NEBULA is almost certainly the result of a supernova explosion which was observed by Chinese astronomers on 4 July 1054. This supernova was so bright that it was risible in full daylight for three weeks. Strangely, however, there is no record of its having been seen in any of the European or Arabian […]
There are about a hundred known supernova remnants in Galaxy. Although visible, X-ray and gamma radiation have been detected from a few of these, most are seen only at radio wave¬lengths. The radio emission is caused by high-speed electrons, produced within the supernova, spiralling around magnetic field lines. This process, called synchrotron radiation, is also […]
The explosion of a supernova SUPERNOVA EXPLOSIONS are the most spectacular events that occur in our Galaxy. During the first week of its supernova phase, a star can reach an absolute magnitude of —20.5, which is 10 billion times more luminous than the Sun, and as bright as many complete galaxies. Supernova explosions are rare […]