Speaker 1: Section twenty seven of Sun, Moon and Stars Astronomy for Beginners.
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Speaker 1: Moon and Stars Astronomy for Beginners by Agnes Giburne, Reading
Speaker 1: the Light, God said let there be light, And there
Speaker 1: was light Genesis one three. Many times in the course
Speaker 1: of this little book, mention has been made of an
Speaker 1: instrument called the spectroscope, to which much of our present
Speaker 1: knowledge of the heavens is due. The subject of spectrum
Speaker 1: analysis is too complex to be fully discussed in a
Speaker 1: volume of this kind, but a few words of explanation
Speaker 1: may be desirable. By means of the spectroscope, we know
Speaker 1: with almost certainty many of the substances which are contained
Speaker 1: in the Sun, in the stars, in nebulae. How large,
Speaker 1: or how far away, or how quickly moving some of
Speaker 1: the heavenly bodies are, could be discovered through the telescope
Speaker 1: without help from the spectroscope. But the actual make of
Speaker 1: them lay, until recent years beyond our grasp, not upon
Speaker 1: Earth alone, but also in the Sun. Exist iron and sodium,
Speaker 1: copper and zinc, magnesium, cobalt, and many other substances with
Speaker 1: which we are familiar, notably hydrogen. Every metal may be
Speaker 1: either in the solid or in the liquid, or in
Speaker 1: the vapor form. Iron, as we commonly see it, is solid.
Speaker 1: In other words, it is frozen like ice. Most metals
Speaker 1: freeze at a much lower temperature than water does. Just
Speaker 1: as a certain increase of heat will turn ice into water,
Speaker 1: so a certain increase of heat will transform solid iron
Speaker 1: into liquid iron. And just as yet greater heat will
Speaker 1: turn water into steam, so very much greater heat will
Speaker 1: transform liquid iron into vapor of iron or iron gas.
Speaker 1: A little heat will do for ice what immense heat
Speaker 1: will do for iron. The intense heat of the Sun
Speaker 1: causes metals which are solid upon Earth to float as
Speaker 1: glowing vapor in the solar atmosphere. Indeed, that dense and
Speaker 1: far reaching atmosphere is largely composed of such metals. Whether
Speaker 1: iron and other earthly metals can be found anywhere in
Speaker 1: or near the sun in anything approaching to a solid
Speaker 1: form is more than doubtful. But in the photosphere they
Speaker 1: probably do exist, in a shape ordering on the liquid form,
Speaker 1: where glowing clouds appear to float formed of condensed and
Speaker 1: radiant metals. This state would answer not to the liquid
Speaker 1: waters of a river, but to the condensed water droplets
Speaker 1: of a fog or cloud. Spectrum analysis, beside teaching us
Speaker 1: what metals may be found in the sun, has also
Speaker 1: a word to say about those which exist in some
Speaker 1: of the stars far distant as those sums of light are.
Speaker 1: We know that in them, too are such earthly materials
Speaker 1: as iron, sodium, magnesium, and a variety of kindred substances,
Speaker 1: while in many of them hydrogen predominates. But how can
Speaker 1: we know all this? How could the wildest guessing grow
Speaker 1: to more than a guess and reveal to us the
Speaker 1: actual presence in even our own particular sun of iron
Speaker 1: or hydrogen, not to speak of more diday distant suns.
Speaker 1: We know it by means of spectrum analysis. The spectroscope
Speaker 1: may be looked upon as twin sister to the telescope.
Speaker 1: A telescope gathers together widely scattered rays of light into
Speaker 1: a spot or focus for our use. The spectroscope separates
Speaker 1: those rays of lights into ribbons, sorts them, and enables
Speaker 1: us to read in them hidden meanings. When a ray
Speaker 1: of light reaches us from the sun, that ray is white,
Speaker 1: but in the whiteness other hues are hidden. A white
Speaker 1: ray is composite in form, made up of many lesser
Speaker 1: rays of diverse colors blended together. Newton was the first
Speaker 1: to discover so much. If a sunlight ray is allowed
Speaker 1: to pass through a small round hole in the wall,
Speaker 1: it will fall upon the opposite wall or upon the ground,
Speaker 1: in a little round patch of light. But if a
Speaker 1: piece of glass cut into the shape of a prism
Speaker 1: is placed in the path of that sunbeam, the round
Speaker 1: patch of light vanishes. In its stead appear several bands
Speaker 1: of soft color, each overlapping and melting into the next. Red, orange, yellow, green, blue, indigo, violet.
Speaker 1: All these become visible. The arrangement of colors is invariably
Speaker 1: the same. Now the prism has done two things. First,
Speaker 1: it has bent the ray out of a straight course,
Speaker 1: causing it to fall in a different place from where
Speaker 1: the round spot lay. Secondly, it has broken up or disintegrated,
Speaker 1: the white ray into those differently tinted rays of which
Speaker 1: it was made. And the manner of breaking it up
Speaker 1: is simply this, that one color is always more or
Speaker 1: less bent than another color in passing through a prism. Therefore,
Speaker 1: all the different tints fall upon different places. The whole
Speaker 1: variegated band, whether of sunlight or of any other light,
Speaker 1: is known as the spectrum of that light, and the
Speaker 1: breaking up of the ray and searching into its make
Speaker 1: is called the analysis of it. Thus the reading of light,
Speaker 1: whether earthly light, moonlight, sunlight, or starlight, is included under
Speaker 1: the head of spectrum analysis. At the so called lowest
Speaker 1: end of the spectrum lies red, the least bent of
Speaker 1: all the colored rays. Of the so called highest end
Speaker 1: lies violet, the most bent. All other hues visible to
Speaker 1: our eyes are placed between light. Beyond the violet and
Speaker 1: below the red. We cannot see. That is, by no
Speaker 1: means to say that it does not exist. We can
Speaker 1: feel the warmth of rays below the red, although we
Speaker 1: cannot see them, and photographs are taken by means of
Speaker 1: rays beyond both the red violet, albeit they are to
Speaker 1: us invisible. By means of those faint rays, photographs can
Speaker 1: actually be taken of countless stars, which no living man
Speaker 1: can see through the most powerful telescopes. For the rays
Speaker 1: are there, however, faint, and they will slowly impress their
Speaker 1: image upon prepared sensitive paper long exposed to their dim shining,
Speaker 1: though human eyes cannot gaze long or steadily enough to
Speaker 1: detect them. Suppose now that for the round hole in
Speaker 1: the wall we substitute a very narrow slit. Then, letting
Speaker 1: the sunshine again stream through, we once more place a
Speaker 1: prism of glass in the path of the ray. When
Speaker 1: it has entered the slit, bright bands of color are
Speaker 1: perceived anew arranged, always in the same order, from red
Speaker 1: to violet. But the different colors no longer overlap as before,
Speaker 1: and in addition to the bright hues, a great many slender,
Speaker 1: dark lines or gaps in the coloring are to be seen.
Speaker 1: These dark lines in the spectrum of sunlight were for
Speaker 1: a long while a great perplexity. At first it was
Speaker 1: thought that they might be caused by something in our
Speaker 1: own atmosphere, but this notion had to be given up.
Speaker 1: It became manifest that the lines were somehow connected with
Speaker 1: the sun, not with the earth. Whenever a ray of
Speaker 1: sunlight was passed through a narrow slit and analyzed there,
Speaker 1: they were always the same in position. More and more
Speaker 1: of them were found through closer observation, but the old
Speaker 1: ones did not change. A ray of moonlight was found
Speaker 1: to contain exactly the same dark lines as a ray
Speaker 1: of sunlight, and most naturally, for a ray of moonlight
Speaker 1: really is nothing more or less than a ray of
Speaker 1: sunlight reflected from the moon. But in a ray of
Speaker 1: starlight the lines were found to be in time different,
Speaker 1: and this alone is enough to do away with the
Speaker 1: idea of the lines being due to something in our air.
Speaker 1: Starlight and sunlight, both alike journey through Earth's atmosphere. Every
Speaker 1: star has its own particular spectrum, sometimes bands of color,
Speaker 1: like our sun's spectrum with fine dark lines. Only the
Speaker 1: arrangement of lines is never the same as those of
Speaker 1: our sun, and it is never the same in any
Speaker 1: two stars. These dark lines in sunlight and starlight tell
Speaker 1: us much and briefly, as follows. If the light of
Speaker 1: a white hot metal, either solid or liquid, is allowed
Speaker 1: to pass through the slit and prism of a spectroscope,
Speaker 1: bands of bright color are seen, one passing into another,
Speaker 1: as with the solar spectrum, but under ordinary conditions of
Speaker 1: bodies in a gaseous state, the spectrum does not consist
Speaker 1: of broad, hazy bands of color, but of sharp bright
Speaker 1: lines and mark this. Each particular gas has its own
Speaker 1: especial lines, always occupying the same position. A chemist knows
Speaker 1: to a certainty how many lines will be seen in
Speaker 1: the case of iron gas, or sodium gas or hydrogen gas,
Speaker 1: and where each line will fall. But suppose mark this again,
Speaker 1: that the light comes either from a solid or a
Speaker 1: liquid or a highly compressed gas, and passes on its
Speaker 1: way through a gas medium at a lower temperature, such
Speaker 1: as a gas flame or glowing gas atmosphere. In such
Speaker 1: a case, when the ray has gone through slit and
Speaker 1: prism and has spread out its spectrum of color bands,
Speaker 1: dark lines will be seen in those bands. These dark
Speaker 1: lines are gas or breaks in the light. They mean
Speaker 1: the absence of part of the sunlight or starlight for
Speaker 1: the gas through which that light has traveled on its way.
Speaker 1: Hitherwood has absorbed or captured part of the light, and
Speaker 1: only part has been free to continue its journey. A
Speaker 1: ray of light from the Sun's photosphere has to pass
Speaker 1: through the Sun's atmosphere of gases, and as it passes,
Speaker 1: each gas in the solar atmosphere takes possession of some
Speaker 1: part of it, producing dark lines which are peculiar to
Speaker 1: that gas. In consequence of this, hundreds of tiny breaks
Speaker 1: are formed in the solar spectrum where the much robbed
Speaker 1: ray falls. If the light of a sodium flame is
Speaker 1: passed through the spectroscope, two bright lines are always seen,
Speaker 1: always in the same position. But in the Sun's coloured spectrum,
Speaker 1: those two lines are dark, for the sodium in the
Speaker 1: Sun's atmosphere has absorbed or stolen exactly that part of
Speaker 1: the sunlight which would have given the two bright sodium lines.
Speaker 1: The spectrum of our means not two, but hundreds of
Speaker 1: bright lines in the solar spectrum. These hundreds of lines
Speaker 1: are dark because the iron gas in the atmosphere of
Speaker 1: the Sun has absorbed all that part of the light
Speaker 1: ray on its journey from the radiant photosphere. Therefore, when
Speaker 1: certain dark lines are apparent in the spectrum of the
Speaker 1: Sun or of a star, we know that the metal
Speaker 1: which always shows exactly corresponding bright lines is present in
Speaker 1: the atmosphere of that sun or star. By the same mode,
Speaker 1: the make of comets, of nebulae, and of other heavenly
Speaker 1: bodies can be tested and examined. This may give just
Speaker 1: a faint idea of the first principles of a new
Speaker 1: grand branch of astronomy, included under the head of spectrum analysis.
Speaker 1: The science is a science of itself, however, and one
Speaker 1: full of complexity. Chemistry and astronomy here walk hand in hand,
Speaker 1: and the spectroscope alone can decide whether any particular star
Speaker 1: is in fact a sun. If the rainbow tinted ribbon
Speaker 1: of light is there crossed by thin dark lines due
Speaker 1: to the stellar atmosphere through which each ray has passed
Speaker 1: after quitting the photosphere, then that star may be counted
Speaker 1: a true sun. Such stars constitute the majority among the
Speaker 1: hosts of Heaven, yet variety without limit is found. In
Speaker 1: one star, the light from the photosphere is almost lost,
Speaker 1: almost absorbed by the surrounding atmosphere. In another, the light
Speaker 1: of the atmosphere so overpowers that of the photosphere that
Speaker 1: only bright gas lines are seen in the spectroscope, the
Speaker 1: continuous color band being comparatively faint. Besides telling us of
Speaker 1: the make of the stars, the spectroscope also speaks to
Speaker 1: us of their motions. A very tiny shift movement of
Speaker 1: the little dark lines or bright lines to right or
Speaker 1: left is sufficient. From this can be calculated with it
Speaker 1: is believed astonishing exactness the rate at which a star
Speaker 1: is rushing towards us or rushing away from us. For
Speaker 1: if the star is nearing our earth, the light waves
Speaker 1: coming from him are pressed together, so to speak, hurrying
Speaker 1: one upon another, while if the star is retreating, the
Speaker 1: light waves are affected in a reverse manner, delayed or
Speaker 1: pulled apart, if such a term may be used. By
Speaker 1: this method, also stars are discovered so dim as to
Speaker 1: be not only utterly invisible to the naked eye, but
Speaker 1: undiscoverable by the telescope. End of Section twenty seven.