Bun-Spot.

Manawatu Herald, 12 January 1897, Page 3

Bun-Spot.

Attention is now drawn to a large dark disc observable on the sun, it is best noticed with the naked eye of an evening when the smoke enables one to look direct at it, otheiwise a smoked glass is necessary. This is a " son-spot," and is one of the dark patches from 1000, to 100,000 miles in diameter, which are often visible upon the photosphere. The central part, or umbra, appears nearly black, though the darkness is really only relative to the intense surrounding brightness. With proper appliances the umbra itself is seen to contain still darker circular holes, and to be overlaid by films of transparent cloud. It is ordinarily surrounded by a nearly concentric penumbra composed of converging filaments, Often, however, the penumbra h unsymmetrical with respect to the umbra, and sometimes it is entirelj wanting* The spots often appeal* ie groups, and frequently a large one breaks up into smaller ones. The) are continually changing in fora and dimensions, and sometimes havi a diitinet drift upon the sun's surface. They last from a few hours to

many months. They are known to be shallow cavities in the photosphere, depressed several hundred miles below the general level, and owe their darkness mainly to the absorption of light due to the cooler vapours which fill them. Their cause and the precise theory of their formation are still uncertain, though it is more than probable that they are in seme way connected with descending currents from the upper regions of the solar atmosphere. The spots are limited to the region within 45 degrees of the sun's equator, and are most numerous in latitudes from 15 to 20 degrees, being rather scarce on the equator itself. They exhibit a marked periodicity in number; at intervals of about eleven years they are abundant, while at intermediate times they almost vanish. The explanation af this periodicity is still unknown. Numerous attempts have been made to oorralate it with various periodic phenomena upon the earth— with doubtful success, however, except that there ii an unmistakable (though unexplained) connection between the spottednets of the sun's surface and the number and violence of our so-called magnetic storms and auroras.