OUR NEAREST STAR

The good news this month comes from Denmark where a remarkable correlation between solar activity and global climate has been discovered. As usuaL the bad news comes from Washington, where Reilly rides again, waving manipulated data and screaming "The ozone layer is going! The ozone layer is going!" The two are connected, and we start with the sun.

The sun is our nearest star; compared with the earth, it is 1.3 million times larger in volume, and 333,000 larger in mass. This alone suggests that its radiation and fluctuations are likely to affect the earth's atmosphere more than Mrs. Reilly's refrigerator or Billy Boys deodorant spray.

The sun rotates, but since it is not a solid body, but a gaseous sphere, its equatorial parts rotate faster than those closer to the poles; the mean length of rotation is about 27 days. The sun is a giant thermonuclear reactor producing energy mainly by fusion of deuterium (hydrogen with an extra neutron in its nucleus) into helium similar to the fusion just achieved in England. The energy is released in the form of several types of radiation: electromag-netic radiation across the entire spectrum from radio waves through visible light to gamma rays; but the sun also spews out streams of particles such as electrons and protons, i.e., corpuscular radiation. (When its particles reach the earth, they are deflected by the geomagnetic field in spiral paths toward the poles where they cause magnetic disturbances, northern lights and other phenomena.)

The solar constant giving the power flow per unit area near the earth at its mean distance fron the sun was long thought to be a constant (1,374 kW/m^2), reduced by the atmospheric absorption to the "insolation" at the earth's surface to about 900 W/m^2. The former constant (in outer space) was the result of calculations from the data at various heights in the atmosphere. Only since the mid-1970s was it possible to measure it directly by satellites; and this revealed that the solar constant was not a constant at all, but fluctuated with solar activity.

Solar activity comprises a number of short-lived phenomena on the sun, such as sun spots, protuberances, and eruptions. Sun spots are on occasion so large that they can be observed with the naked (but protected) eye, which is why they have been known since anti-quity. A regular record has been kept on them since 1750 by an observatory in Zurich, Switzerland. The sunspot number (or "Zurich" num[b]er) 10g + s, where s is the number of spots and g the number of groups of merging spots (in effect regarding each group as containing 10 spots) has proved to be a good measure of solar activity in general. Its record over the last 240 years shows that it periodically rises and diminishes again. The average length of a cycle is 11 years, though its duration from one maximum to the next may vary within +/-4 years.

[Strictly speaking, these are half-cycles of a 22-year cycle; the matter that churns in the sunspot eddies rotates clockwise for 11 years, and when they reappear during the next cycle, the direction of rotation, and therefore also of the accompanying magnetic field, is reversed.]

For the discussion of Billy Boy's concocted data in the following, it is important to note that the last solar minimum occurred in 1986, and we are now probably dose to a maximum. (The cycles generally exhibit faster rises and slower declines.)