Both faculae, or hot spots, and prominences are likely to be more numerous and more intense in the neighborhood of large sun-spot groups than elsewhere on the sun. Also, faculae-andprominence activity tends to wax and wane with the sun-spot cycle; the solar eruptions are more prevalent in years of sun-spot maximum. Faculae and prominences, indeed, are probably parts of the same thing viewed from different angles (Pugh 33). The ‘solar constant,’ or measure of the sun’s total radiation, has been measured by complex and ingenious methods devised mainly by Doctor C. G.
Abbot, solar researcher of the Smithsonian Institution in Washington. Measured on the earth’s surface, this entity would be meaningless because of variable atmospheric influences. But the Langley spectro-bolometer and the Abbot pyrheliometer permit aerologist-astronomers reliable to determine the solar constant outside the earth’s atmosphere from terrestrial observations at moderate altitudes. By this method, checked and rechecked many times, the average value of the solar constant, outside the earth’s atmosphere at mean earth-sun distance, is found to be about two calories (1.
94, to be exact) per square centimeter per minute. That is to say, the solar radiation falling squarely on a centimeter (. 6 inch) cube of water would, if entirely absorbed, raise the water temperature about 2° C. (around 3° F. ) per minute (Hoyt and Schatten 54-56). From the mean of the solar constant values reported by its three mountain-top stations, the Smithsonian Institution is enabled to plot with confidence a curve which represents the actual day-to-day, month-to-month, and year-to-year variations in the solar constant.
At first glance this curve resembles nothing so much as a profile of the Alps, and seems to show no regular periodicity. But a complicated machine is available which can analyze such a complex curve; it can, for example, break up the complex and irregular curve representing the playing of an organ into the pure and regular vibrations representing the fundamental notes that go to make up a chord, and all their separate overtones. In the same way, this machine analyzes the complex output curve of the solar light-organ; and finds that, in addition to the fundamental periods measured in years, there are many overtones measured in months.
And there is, of course, the twenty-seven-day period imposed by the sun’s rotation. The changes in the constant of total solar radiation are small, seldom exceeding three per cent. And it is fortunate for us earthlings that they are; for if the constant changed by as much as fifty per cent, life would vanish from the face of the earth (Pugh 27). Of all the electro-magnetic energy wave lengths radiated by the sun, the shorter wave lengths vary the most in response to solar disturbances.
Though only a small fraction of the total radiation is in the ultra-violet region, this region suffers the greatest changes with the changing solar constant, and may mainly account for some of the earthly echoes that respond to the solar chords. Around 1932 Edison Pettit of Mount Wilson Observatory devised an instrument which measures the ratio of the sun’s ultra-violet to its visible light. As a sample of visible light Pettit chose green, in the center of the visible spectrum. To get green and no other color one might use a filter such as those used in three-color photography – perhaps a piece of green glass.
But Pettit wanted a narrower band of green than most people (at about 5300 a. ), so he chose for his filter a film of pure gold thin enough to be translucent. And for his ultra-violet filter, to admit the short-wave radiation and nothing else (at about 3200 a. ) he chose a thin, translucent film of pure silver. Pettit found that there seemed often to be relation between sun-spot activity and the sun’s output of ultra-violet (which varies from time to time by fifty per cent or more), at least during the shorter-period fluctuations.
He also found that the ultra-violet varies more or less with, but more widely than, the solar constant of total radiation (Hoyt and Schatten 67). All in all, I may admit that a lot can be written (and I hope some day to write) about the earth and the sun – about all the fascinating and portentous happenings within the sun, and about their terrestrial effects in the way of radio interference, aurora, magnetic storms, and atmospheric storms.
The sun is perceived as a mundane star in astronomical sphere. In this we are undoubtedly lucky, because if the sun’s variations happened to be too violent, Earth could not have been a safe place for the evolution of life, as it demands great stability for hundreds of millions of years. However, evidently, the sun displays a wide range of exciting astrophysical phenomena in interesting, but modest, variations; one of the greatest, definitely, are undoubtedly, sunspots.
Bond, Peter. “Hubble’s long view. ” Astronomy & Geophysics. Volume 45 Issue 3, 2004. Hoyt, Douglas V. and Schatten, Kenneth H. The Role of the Sun in Climate Change. Oxford University Press, 1997. Kedzie, John Hume. Solar Heat, Gravitation, And Sun Spots. Kessinger Publishing, LLC 2008. MacRobert, Alan. “The Leonid Meteors: Waiting and Watching”. Sky & Telescope, November 1996. Pugh, Philip. Observing the Sun with Coronado Telescopes. Springer; 1 edition, 2007.