Home >> Encyclopedia Americana, Volume 26 >> Analysis to Or The Me Chanical >> Slimy_P1


sun, light, centre, limb, dark, atmosphere, earth, heat and miles

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SLIMY, soo'ine, Rusiia, a town in the gov ernment of Kharkov, on the river Psiol, 83 miles north of the town of Kharkov. It has nine churches, a gymnasium, technical school, banks and a large sugar refinery, besides nu merous distilleries. The soil is productive, and agricultural products are exported together with brandy. Four annual fairs give considerable impulse to trade. Pop. 51,500.

SUN, the great central body of the solar system. The aspect of the sun with which all are familiar from infancy shows that it is a shining globe. Astronomical measurements show that this globe is more than 100 times the diam eter of the earth, and, therefore, more than 1,000,000 times its volume. Its small apparent diameter is dpe to its enormous distance of 93,000,000 miles. The following are more ,exact numerical particulars: Mean distance (miles) 92,900,000 Eqhor. parallax 8.80" Density (water = I) 1.41 Mass (earth =1) 332,800 Diameter (miles) 866,400 Gravity (earth's =1) 27.65 For methods of determining the distance and other quantities see Astaormsiv, Theoretical. The aim of the present article is to set forth the physical constitution of the sun, so far as modern research has made it known.

One of the most certain results of research is that the sun is at an extremely high tempera ture, higher than any that we can produce in our furnaces. This is shown by two consider ations. One is the enormous amount of energy radiated, which suffices to keep the earth warm and support life on its surface, notwithstanding the immense distance at which it is placed Nothing but a hot body could radiate so great a volume of energy. Another proof of the high temperature is shown by the spectroscope, which discloses the vapor of iron and other refractory metals in the sun's atmosphere. It requires a hot furnace to melt iron. Much higher must be the temperature which would make it boil away like water. The temperature of the sun not only does this, but the fact that the spectral lines of iron are dark on a bright ground shows that the solar light emanates from a body yet hotter than the vapor of iron.

Aspect of the We can see only the surface of the sun, not its vast interior. To distinguish the two, the shining surface is called the °photosphere.° The latter presents to our view the appearance of a flat disc. The edge of this disc is called the °limb.° When seen without telescopic magnification, through a dark glass or other medium, the disc of the sun ap pears quite uniform, slightly shading off in tint at the limb. But when carefully examined with the telescope, under good atmospheric condi tions, the entire photosphere appears as a dark ish background, sprinkled with brighter grains or nodules. These are quite ir

regular in size and form, and appear as if bright on a relatively dark or yellowish back ground. It is probable that they are produced by currents of heated matter from the interior, hereafter to be described, which are constantly rising to the surface, there to radiate their heat and then fall back again. When the intensity of the heat radiated from different parts of the photosphere is accurately measured, it is found that the amount of radiation diminishes from the centre of the disc to the limb, where it is least. The diminution is slow at first, but in creases quite rapidly at the limb, where it is little more than one-half of that at the centre. The light diminishes in a still greater ratio than the heat. The tint of the light is also different scope was first pointed at the sun, the observers were surprised to find that that object was now and then variegated by dark spots. These were observed by Galileo, Scheiner and Fabritius. The two latter published more or less elaborate treatises on the subject, but with their imperfect instruments they were not able to learn much as to the laws of these objects. We now know, with the modern perfected methods of observa tion, that the spots are of very different sizes, ranging from the minutest point visible in the telescope to a size so great as to be perceptible to the naked eye. The largest must, therefore, exceed the earth itself in diameter. These ob jects are usually very irregular in their outline, being frequently jagged and cornered, as if made by a shot or bunch of shot passing through a tin plate or wooden plank They frequently appear in groups; indeed a spot vis ible to the naked eye commonly consists of a at the centre and at the limb, although this would hardly be noticed by the eye. The light at the limb has more red in its composition than at the centre. This effect is especially noticeable at the time of a total or annular eclipse of the sun. When the moon has nearly covered the sun, the remaining light has a lurid aspect, as if the sun were shining through a smoky atmosphere, thus giving to observers the illusion that the sky is hazy. There can be no doubt of the cause of this appearance. The sun, like the earth, is surrounded by an atmos phere; but this atmosphere is cooler than the photosphere which sends out the light and heat. The existence of the atmosphere is demon strated by the lines of the spectrum, as well as by the absorption of heat at the limb, which is greater than near the centre because the light coming from that portion of the photo sphere has to pass through a greater depth of the atmosphere than when it rises directly upward from the centre.

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