The Astronomical Radiative Stability

Abstract

ASTRONOMERS are doubtless not unaware of the enormous radiative uniformity that is demanded by the permanence of organic life on the earth. If the temperature at the earth's surface were altered even for a single season from its actual value about, say, 27° C. or 300° K., by 50° in excess or defect, all terrestrial organic life would be blotted out never to return. This would happen if even only once in the hundred million years demanded for terrestrial organic evolution the effective temperature of the solar radiating surface changed from the present mean value 6,000° K. by 1,000° in excess or defect, if it were a matter of steady state, while during the time of this change the stream of radiation incident on the earth would be altered in a proportion much greater. On current theories the difference between the top and bottom of the radiating solar atmosphere would be great in comparison with this figure, and lower down vast temperatures are soon reached. This shows how extremely steady the balance must be, and how slight the solar evolution must have been even in that vast time. As one result, the sunspot disturbances, even though they occupy only a very small part of the area of the solar disc, would have to be purely superficial phenomena. The output of radiation is very steady, as from a steady interior; yet the heavens are full of variable stars. Perhaps these considerations were remotely in view when long ago Whewell and Brewster were discussing the plurality of worlds, and Huxley championed the geologists against Kelvin.