COMETS’ LUMINOSITY

Evening Star, Issue 20138, 1 April 1929, Page 10

COMETS’ LUMINOSITY

An important advance in our knowledge of comets has just been announced to the Koval Astronomical Society by Professor if. Zanstra, of the Imperial College of Science and Technology, who describes the result of 1 theoretical researches which he; has made into the cause of the luminosity of these bodies (says the ‘ Morning Post’). It is, perhaps, not generally known that the greater part, if not the whole, of the luminosity of a comet exists only when the body is in the neighbourhood of the sun. In the distant parts of its orbit a comet shines, if at all, with only a very feeble light, and is not observed from the earth, i t then consists simply of a “head,” which is a collection of meteorites; the “tail,” like the luminosity, is formed only when the comet approaches the sun, and is, doubtless, duo to the action of the sun's heat in liberating from the meteorite's gases which have been absorbed or “ occluded ” there. The spectroscope shows that the light of a comet, in addition to ordinary re- , - fleeted sunlight, consists of radiations r of carbon monoxide, sodium, iron, and i other substances. These substances must exist in the comet and bo stimn- ' "lated in some way by the sun to radiate their own peculiar light waves. The mechanism by which the. sun stimulates them, however, has been unknown, and only vague speculations have been put forward. Professor Zanstra lias now considered the matter in detail from the point of view of modern atomic theory, " and has examined in particular whether the ordinary light of the sun is snfli- - ...uient to cause the observed luminosity without resorting to the special hypoI.kthetical radiations which have sometimes been suggested. He linds that it is. ■ The atoms of the gases in the comet .when in the neighbourhood of a strong ‘’’beam of sunlight are made to shine by a prove .s closely akin to “ Jlnorcscence ” —a phenomenon with which, in a slightly different form, wo are fami■“"'liar in luminous paint, phosphorescent etc. * Professor Zanstra has carried his ro- "‘ Searches further, and has shown that his theory explains another puzzling fact. Although the spectroscope shows that carbon mcrr-Txids, for example, exists in comets, the radiations of this substance whicli it reveals are only a part of the radiations of the same substance produced in the laboratory. The absence of the other part has previousl'"' been unexplained. .Oh Professor Zanstra’s views, how■ever, this is just what would bo expected, for he has shown that the intensity of the sunlight is sufficient to stimulate the observed part of the radiation but insufficient to stimulate r -tlie unobserved part up to the limit of ‘"'Visibility. This constitutes strong support for the theory, which represents one' of the most notable advances in our know ledge of cometary phenomena made in recent times.