Sunday, May 25, 2008

A Study of The Sun



How It May Be Observed Without Danger. A Method of Getting a Perfectly Pure Beam For Inspection — A Lesson In Astronomy Couched In Simple Terms.

Every day a royal presence, attended by numerous unseen courtiers, sweeps across the sky. The sun looks us so boldly in the face that we are compelled to veil ourselves from his accursing gaze. Let us commence our now studies by contemplating his attractiveness.

A piece of well smoked glass will give us good service. If this be covered with another piece, with strips of paper at the edges to separate them and prevent rubbing, and other mucilaged strips to bind the outer edges, we shall have a respectable and lasting astronomical instrument.

The eye may now examine the dazzling orb without danger, and it will discover a disk which is apparently no larger than that of the full moon, but the fact that the sun is about 400 times farther away accounts for the resemblance in size. But the disk is not all of the immense world, for a very important envelope of vast dimensions is invisible except to special instruments. The limb of the sun is seen to be not quite so bright as the central portions, because the light from it has to penetrate a greater depth of atmosphere.

Occasionally we see a "spot" upon the solar surface, in which case it must be very large, but if we are fortunate enough to have access to even a small spyglass we shall many times see spots. There are years when the spots are very numerous (the writer counted 168 one day and more than 300 on a day in 1893), and years when none is seen for months, and this appears to be governed by a "period" of about 11 years.

If we use a telescope with our smoked glass, the spectacle will be curiously interesting, for the object glass — a very large eye — gathers many rays of light and bends them to a focus, producing a magnified image which is yet more enlarged by the eyepiece, which is a microscope. Now, the very grain of the sun, so to speak, is visible, the surface being completely flecked with gray white matter, while here and there huge masses of white protrude. These latter are called faculae and are usually associated with the spots which are depressions in the surface — deep, dark cavities, but dark only as contrasted with the shining regions, for they are brighter than the calcium light. Very recently the writer measured a large group and found that it occupied an area of more than 100,000 miles in length and about three-fourths as wide, into which could be cast 100 earths without crowding them. Still larger groups have sometimes been noticed. Watching the spots from day to day reveals the time of revolution of the sun upon its axis, about 25 days, which means that one day on the sun is as long as 25 of ours.

As yet the sun has not yielded the secret of its composition, and the telescope, unaided, is inadequate to solve the mystery. Perhaps in childhood we beguiled hours of church service, which were a trifle wearisome to little ones, by noticing the play of color in the "lusters" which hung in profusion from the old fashioned lamps. How little we dreamed that the sun was whispering through this simple medium intelligible messages of very high importance, for this three faced form of glass is called a prism, the change of direction of objects viewed through it being due to the bending (refraction) of the rays of light passing through it, and the color fringe along the edges of the images the primary rays of which white light is composed, which is easily proved by passing the colored rays through another prism, when they form a beam of white light once more.

The same color band, or spectrum, is shown by a grating of parallel wires strung in a frame, or by a close grained feather, or even by the eyelashes when the eye is half closed.

But we can easily improve upon these primitive instruments by employing a series of prisms of fine construction or a grating produced by ruling lines with a diamond upon a piece of perfectly flat and highly polished speculum metal.

To get a perfectly pure beam for inspection we let the telescopic image of the sun fall upon a delicate slit in a metal plate, which is in the focus of the object glass of a little telescope, whose duty it is to make parallel the rays to be examined, and which sends them through the series of prisms referred to or causes them to fall upon a grating. In either case they are viewed by another little telescope, and the beam of sunlight tells its story in a magnificent spectrum, far exceeding the rarest touches of world renowned artists.

Now for the precious secret! The beautiful color band is threaded with thousands of slender dark lines, which correspond with the bright lines, which are the sign manual of metals in a glowing state, and we need only to put a pinch of salt in the flame of a candle and let the light fall alongside the sun's image on the slit, when there will be two spectra, side by side, and the two bright yellow lines of sodium will exactly coincide with two black lines in the orange of the solar spectrum, and the crowning proof appears when the calcium light is permitted to shine through the candle flame, instantly turning the bright lines to dark ones. So with the lines of other metals.

We have learned from the sun's own messages, after a journey of 93,000,000 miles, that it is a gaseous body; that many of the metals of earth are vaporized in its awful temperature, and that the surface is probably a shell of luminous clouds surrounded by an "atmosphere" of gases thousands of miles deep, out of which spurt for hundreds of thousands of miles, with a speed in contrast with which the movement of whirlwinds on earth is a dead calm, jets of flaming hydrogen intermingled with the metallic vapors, which, becoming cooled by exposure to the cold of space, fall upon the surface and cause the depressions known as spots. — Philadelphia Ledger.

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