100 YEARS AGO

Though Jupiter has been unfavourably placed for European observers during the present year, his surface markings have been extremely interesting, of great variety and in plentiful numbers. The English climate, even at its best, can scarcely be said to suit astronomical work in an eminent degree, but its characteristics in 1902 have proved unusually bad... The most noteworthy incident in connection with recent studies of Jupiter is to be found in a very pronounced acceleration of motion in the great red spot. This first made itself evident in 1901, but it has been intensified during the past summer. For about twenty-three years, uninterruptedly, this singular marking had exhibited a constantly increasing retardation, which caused its rotation period to lengthen from about 9h. 55m. 34s. to nearly 9h. 55m. 42s. But in 1901 it declined to 9h. 55m. 41s. and during the present year the rate has been about 9h. 55m 39½s. And this increase in velocity has been contemporary with the outbreak of a large, irregular or multiple marking of a dusky hue, in the same latitude of the planet.

From Nature 18 December 1902.

50 YEARS AGO

The existence of discrete sources of extra-terrestrial radio-frequency radiation is now well established and the positions of more than one hundred sources have been published. Attempts to identify these sources with any particular class of visual object have so far failed, and the origin of the radiation remains unexplained. One of the fundamental requirements in the study of these sources is a knowledge of their apparent angular size, and although attempts to make this measurement have been made by several observers, it has proved to be beyond the resolving power of their equipment. The present communication gives a preliminary account of a successful attempt to measure the angular size of the two most intense sources... The measurements are not yet adequate to define satisfactorily the shape of the sources or the distribution of intensity across their disks. Further observations are now being made... We wish to thank Dr. R. Q. Twiss for his assistance with the mathematical theory, and Prof. A. C. B. Lovell for making the necessary facilities available and for his interest in the investigation.

R. Hanbury Brown, R. C. Jennison & M. K. Das Gupta

From Nature 20 December 1952.