X-Ray Astronomy

This paper reviewed X-ray data that have been recently accumulated by space instruments and described a most remarkable experiment relating to X-ray emission from the Crab Nebula. This nebula is the remnant of a supernova explosion in the year 1054 AD. The question was whether the X-radiation eminated from a point source, indicating possibly an invisible neutron star, or from a more diffuse source. Detector angular resolution was entirely inadequate for such a measurement so it was decided to use the moon for a shutter. An occultation by the moon occurs only once in 9 years. The detectors were carried above the atmosphere on a rocket, providing 5 minutes to make the observation. In spite of the seemingly impossible timing requirements, further complicated by X-rays from the sun, the experiment was successful and showed that the source was about 1 light year in diameter. See "Lunar Occultation of X-ray Emission from the Crab Nebula," Bowyer, Byram, Chubb and Friedman, Science, 146, p. 912, 13 Nov. 1964. (W.A.H.)