WEBVTT 1 00:00:00.720 --> 00:00:06.639 Section twenty seven of Sun, Moon and Stars Astronomy for Beginners. 2 00:00:07.280 --> 00:00:11.080 This is a LibriVox recording. All LibriVox recordings are in 3 00:00:11.119 --> 00:00:15.839 the public domain. For more information or to volunteer, please 4 00:00:15.960 --> 00:00:22.559 visit LibriVox dot org. Read by Jennifer beckett Wood Sun 5 00:00:22.920 --> 00:00:30.120 Moon and Stars Astronomy for Beginners by Agnes Giburne, Reading 6 00:00:30.160 --> 00:00:35.920 the Light, God said let there be light, And there 7 00:00:36.119 --> 00:00:42.159 was light Genesis one three. Many times in the course 8 00:00:42.200 --> 00:00:44.799 of this little book, mention has been made of an 9 00:00:44.799 --> 00:00:48.759 instrument called the spectroscope, to which much of our present 10 00:00:48.880 --> 00:00:52.679 knowledge of the heavens is due. The subject of spectrum 11 00:00:52.719 --> 00:00:55.960 analysis is too complex to be fully discussed in a 12 00:00:56.039 --> 00:00:59.520 volume of this kind, but a few words of explanation 13 00:00:59.719 --> 00:01:04.239 may be desirable. By means of the spectroscope, we know 14 00:01:04.799 --> 00:01:09.120 with almost certainty many of the substances which are contained 15 00:01:09.159 --> 00:01:14.000 in the Sun, in the stars, in nebulae. How large, 16 00:01:14.200 --> 00:01:17.480 or how far away, or how quickly moving some of 17 00:01:17.480 --> 00:01:21.200 the heavenly bodies are, could be discovered through the telescope 18 00:01:21.480 --> 00:01:25.239 without help from the spectroscope. But the actual make of 19 00:01:25.280 --> 00:01:30.239 them lay, until recent years beyond our grasp, not upon 20 00:01:30.319 --> 00:01:35.159 Earth alone, but also in the Sun. Exist iron and sodium, 21 00:01:35.560 --> 00:01:40.959 copper and zinc, magnesium, cobalt, and many other substances with 22 00:01:41.040 --> 00:01:46.920 which we are familiar, notably hydrogen. Every metal may be 23 00:01:47.079 --> 00:01:49.519 either in the solid or in the liquid, or in 24 00:01:49.599 --> 00:01:53.640 the vapor form. Iron, as we commonly see it, is solid. 25 00:01:54.319 --> 00:01:58.680 In other words, it is frozen like ice. Most metals 26 00:01:58.719 --> 00:02:02.519 freeze at a much lower temperature than water does. Just 27 00:02:02.560 --> 00:02:05.920 as a certain increase of heat will turn ice into water, 28 00:02:06.640 --> 00:02:10.360 so a certain increase of heat will transform solid iron 29 00:02:10.400 --> 00:02:14.479 into liquid iron. And just as yet greater heat will 30 00:02:14.479 --> 00:02:18.680 turn water into steam, so very much greater heat will 31 00:02:18.680 --> 00:02:23.400 transform liquid iron into vapor of iron or iron gas. 32 00:02:24.360 --> 00:02:27.639 A little heat will do for ice what immense heat 33 00:02:27.680 --> 00:02:31.680 will do for iron. The intense heat of the Sun 34 00:02:31.759 --> 00:02:35.479 causes metals which are solid upon Earth to float as 35 00:02:35.520 --> 00:02:40.319 glowing vapor in the solar atmosphere. Indeed, that dense and 36 00:02:40.439 --> 00:02:45.479 far reaching atmosphere is largely composed of such metals. Whether 37 00:02:45.560 --> 00:02:49.280 iron and other earthly metals can be found anywhere in 38 00:02:49.639 --> 00:02:52.960 or near the sun in anything approaching to a solid 39 00:02:53.039 --> 00:02:57.759 form is more than doubtful. But in the photosphere they 40 00:02:57.800 --> 00:03:01.400 probably do exist, in a shape ordering on the liquid form, 41 00:03:01.960 --> 00:03:05.919 where glowing clouds appear to float formed of condensed and 42 00:03:06.080 --> 00:03:10.840 radiant metals. This state would answer not to the liquid 43 00:03:10.879 --> 00:03:14.599 waters of a river, but to the condensed water droplets 44 00:03:14.639 --> 00:03:20.280 of a fog or cloud. Spectrum analysis, beside teaching us 45 00:03:20.280 --> 00:03:23.360 what metals may be found in the sun, has also 46 00:03:23.400 --> 00:03:26.039 a word to say about those which exist in some 47 00:03:26.120 --> 00:03:30.879 of the stars far distant as those sums of light are. 48 00:03:31.080 --> 00:03:34.439 We know that in them, too are such earthly materials 49 00:03:34.800 --> 00:03:40.479 as iron, sodium, magnesium, and a variety of kindred substances, 50 00:03:41.000 --> 00:03:46.120 while in many of them hydrogen predominates. But how can 51 00:03:46.159 --> 00:03:49.879 we know all this? How could the wildest guessing grow 52 00:03:49.960 --> 00:03:52.719 to more than a guess and reveal to us the 53 00:03:52.759 --> 00:03:57.120 actual presence in even our own particular sun of iron 54 00:03:57.400 --> 00:04:00.840 or hydrogen, not to speak of more diday distant suns. 55 00:04:02.240 --> 00:04:07.319 We know it by means of spectrum analysis. The spectroscope 56 00:04:07.400 --> 00:04:10.400 may be looked upon as twin sister to the telescope. 57 00:04:11.280 --> 00:04:15.520 A telescope gathers together widely scattered rays of light into 58 00:04:15.560 --> 00:04:20.839 a spot or focus for our use. The spectroscope separates 59 00:04:20.879 --> 00:04:25.120 those rays of lights into ribbons, sorts them, and enables 60 00:04:25.199 --> 00:04:29.360 us to read in them hidden meanings. When a ray 61 00:04:29.399 --> 00:04:33.040 of light reaches us from the sun, that ray is white, 62 00:04:33.560 --> 00:04:37.160 but in the whiteness other hues are hidden. A white 63 00:04:37.279 --> 00:04:40.879 ray is composite in form, made up of many lesser 64 00:04:41.000 --> 00:04:45.879 rays of diverse colors blended together. Newton was the first 65 00:04:46.040 --> 00:04:50.600 to discover so much. If a sunlight ray is allowed 66 00:04:50.639 --> 00:04:53.560 to pass through a small round hole in the wall, 67 00:04:53.800 --> 00:04:57.240 it will fall upon the opposite wall or upon the ground, 68 00:04:57.639 --> 00:05:00.879 in a little round patch of light. But if a 69 00:05:00.920 --> 00:05:03.360 piece of glass cut into the shape of a prism 70 00:05:03.800 --> 00:05:06.879 is placed in the path of that sunbeam, the round 71 00:05:06.959 --> 00:05:11.480 patch of light vanishes. In its stead appear several bands 72 00:05:11.519 --> 00:05:22.240 of soft color, each overlapping and melting into the next. Red, orange, yellow, green, blue, indigo, violet. 73 00:05:22.839 --> 00:05:27.439 All these become visible. The arrangement of colors is invariably 74 00:05:27.480 --> 00:05:32.000 the same. Now the prism has done two things. First, 75 00:05:32.079 --> 00:05:34.480 it has bent the ray out of a straight course, 76 00:05:34.920 --> 00:05:37.360 causing it to fall in a different place from where 77 00:05:37.360 --> 00:05:42.360 the round spot lay. Secondly, it has broken up or disintegrated, 78 00:05:42.360 --> 00:05:46.120 the white ray into those differently tinted rays of which 79 00:05:46.160 --> 00:05:49.240 it was made. And the manner of breaking it up 80 00:05:49.319 --> 00:05:53.279 is simply this, that one color is always more or 81 00:05:53.360 --> 00:05:57.800 less bent than another color in passing through a prism. Therefore, 82 00:05:58.120 --> 00:06:02.160 all the different tints fall upon different places. The whole 83 00:06:02.319 --> 00:06:06.560 variegated band, whether of sunlight or of any other light, 84 00:06:07.079 --> 00:06:10.000 is known as the spectrum of that light, and the 85 00:06:10.040 --> 00:06:13.319 breaking up of the ray and searching into its make 86 00:06:13.759 --> 00:06:17.720 is called the analysis of it. Thus the reading of light, 87 00:06:17.920 --> 00:06:23.720 whether earthly light, moonlight, sunlight, or starlight, is included under 88 00:06:23.759 --> 00:06:28.079 the head of spectrum analysis. At the so called lowest 89 00:06:28.199 --> 00:06:31.399 end of the spectrum lies red, the least bent of 90 00:06:31.439 --> 00:06:35.160 all the colored rays. Of the so called highest end 91 00:06:35.279 --> 00:06:39.720 lies violet, the most bent. All other hues visible to 92 00:06:39.800 --> 00:06:44.439 our eyes are placed between light. Beyond the violet and 93 00:06:44.519 --> 00:06:48.240 below the red. We cannot see. That is, by no 94 00:06:48.360 --> 00:06:51.360 means to say that it does not exist. We can 95 00:06:51.399 --> 00:06:54.720 feel the warmth of rays below the red, although we 96 00:06:54.759 --> 00:06:58.199 cannot see them, and photographs are taken by means of 97 00:06:58.319 --> 00:07:02.279 rays beyond both the red violet, albeit they are to 98 00:07:02.399 --> 00:07:06.959 us invisible. By means of those faint rays, photographs can 99 00:07:07.000 --> 00:07:11.279 actually be taken of countless stars, which no living man 100 00:07:11.319 --> 00:07:15.720 can see through the most powerful telescopes. For the rays 101 00:07:15.759 --> 00:07:19.920 are there, however, faint, and they will slowly impress their 102 00:07:19.920 --> 00:07:25.480 image upon prepared sensitive paper long exposed to their dim shining, 103 00:07:26.120 --> 00:07:29.839 though human eyes cannot gaze long or steadily enough to 104 00:07:29.920 --> 00:07:34.120 detect them. Suppose now that for the round hole in 105 00:07:34.160 --> 00:07:38.600 the wall we substitute a very narrow slit. Then, letting 106 00:07:38.639 --> 00:07:42.360 the sunshine again stream through, we once more place a 107 00:07:42.399 --> 00:07:45.199 prism of glass in the path of the ray. When 108 00:07:45.240 --> 00:07:48.759 it has entered the slit, bright bands of color are 109 00:07:48.759 --> 00:07:52.759 perceived anew arranged, always in the same order, from red 110 00:07:52.759 --> 00:07:57.040 to violet. But the different colors no longer overlap as before, 111 00:07:57.720 --> 00:08:01.240 and in addition to the bright hues, a great many slender, 112 00:08:01.360 --> 00:08:05.000 dark lines or gaps in the coloring are to be seen. 113 00:08:06.560 --> 00:08:09.240 These dark lines in the spectrum of sunlight were for 114 00:08:09.279 --> 00:08:13.120 a long while a great perplexity. At first it was 115 00:08:13.160 --> 00:08:16.079 thought that they might be caused by something in our 116 00:08:16.120 --> 00:08:19.600 own atmosphere, but this notion had to be given up. 117 00:08:20.240 --> 00:08:23.720 It became manifest that the lines were somehow connected with 118 00:08:23.800 --> 00:08:27.639 the sun, not with the earth. Whenever a ray of 119 00:08:27.680 --> 00:08:31.480 sunlight was passed through a narrow slit and analyzed there, 120 00:08:31.560 --> 00:08:35.399 they were always the same in position. More and more 121 00:08:35.440 --> 00:08:38.919 of them were found through closer observation, but the old 122 00:08:38.960 --> 00:08:42.960 ones did not change. A ray of moonlight was found 123 00:08:43.000 --> 00:08:46.000 to contain exactly the same dark lines as a ray 124 00:08:46.039 --> 00:08:50.320 of sunlight, and most naturally, for a ray of moonlight 125 00:08:50.440 --> 00:08:53.159 really is nothing more or less than a ray of 126 00:08:53.240 --> 00:08:57.519 sunlight reflected from the moon. But in a ray of 127 00:08:57.600 --> 00:09:00.720 starlight the lines were found to be in time different, 128 00:09:01.240 --> 00:09:03.480 and this alone is enough to do away with the 129 00:09:03.519 --> 00:09:07.159 idea of the lines being due to something in our air. 130 00:09:07.960 --> 00:09:13.320 Starlight and sunlight, both alike journey through Earth's atmosphere. Every 131 00:09:13.360 --> 00:09:17.720 star has its own particular spectrum, sometimes bands of color, 132 00:09:18.200 --> 00:09:22.399 like our sun's spectrum with fine dark lines. Only the 133 00:09:22.600 --> 00:09:25.639 arrangement of lines is never the same as those of 134 00:09:25.679 --> 00:09:28.440 our sun, and it is never the same in any 135 00:09:28.480 --> 00:09:33.559 two stars. These dark lines in sunlight and starlight tell 136 00:09:33.639 --> 00:09:38.080 us much and briefly, as follows. If the light of 137 00:09:38.120 --> 00:09:41.759 a white hot metal, either solid or liquid, is allowed 138 00:09:41.799 --> 00:09:44.960 to pass through the slit and prism of a spectroscope, 139 00:09:45.440 --> 00:09:49.159 bands of bright color are seen, one passing into another, 140 00:09:49.639 --> 00:09:53.919 as with the solar spectrum, but under ordinary conditions of 141 00:09:53.960 --> 00:09:57.679 bodies in a gaseous state, the spectrum does not consist 142 00:09:57.759 --> 00:10:01.480 of broad, hazy bands of color, but of sharp bright 143 00:10:01.720 --> 00:10:07.159 lines and mark this. Each particular gas has its own 144 00:10:07.320 --> 00:10:12.759 especial lines, always occupying the same position. A chemist knows 145 00:10:12.799 --> 00:10:16.000 to a certainty how many lines will be seen in 146 00:10:16.039 --> 00:10:20.080 the case of iron gas, or sodium gas or hydrogen gas, 147 00:10:20.480 --> 00:10:25.519 and where each line will fall. But suppose mark this again, 148 00:10:26.080 --> 00:10:28.519 that the light comes either from a solid or a 149 00:10:28.600 --> 00:10:32.480 liquid or a highly compressed gas, and passes on its 150 00:10:32.480 --> 00:10:35.919 way through a gas medium at a lower temperature, such 151 00:10:35.919 --> 00:10:40.399 as a gas flame or glowing gas atmosphere. In such 152 00:10:40.399 --> 00:10:42.960 a case, when the ray has gone through slit and 153 00:10:43.080 --> 00:10:46.360 prism and has spread out its spectrum of color bands, 154 00:10:46.879 --> 00:10:50.759 dark lines will be seen in those bands. These dark 155 00:10:50.840 --> 00:10:54.360 lines are gas or breaks in the light. They mean 156 00:10:54.399 --> 00:10:58.759 the absence of part of the sunlight or starlight for 157 00:10:58.840 --> 00:11:01.559 the gas through which that light has traveled on its way. 158 00:11:01.639 --> 00:11:05.519 Hitherwood has absorbed or captured part of the light, and 159 00:11:05.639 --> 00:11:09.840 only part has been free to continue its journey. A 160 00:11:09.960 --> 00:11:13.159 ray of light from the Sun's photosphere has to pass 161 00:11:13.240 --> 00:11:16.919 through the Sun's atmosphere of gases, and as it passes, 162 00:11:17.480 --> 00:11:20.919 each gas in the solar atmosphere takes possession of some 163 00:11:21.120 --> 00:11:24.960 part of it, producing dark lines which are peculiar to 164 00:11:25.000 --> 00:11:29.600 that gas. In consequence of this, hundreds of tiny breaks 165 00:11:29.600 --> 00:11:32.720 are formed in the solar spectrum where the much robbed 166 00:11:32.840 --> 00:11:36.519 ray falls. If the light of a sodium flame is 167 00:11:36.600 --> 00:11:40.559 passed through the spectroscope, two bright lines are always seen, 168 00:11:41.240 --> 00:11:45.360 always in the same position. But in the Sun's coloured spectrum, 169 00:11:45.519 --> 00:11:49.000 those two lines are dark, for the sodium in the 170 00:11:49.039 --> 00:11:53.639 Sun's atmosphere has absorbed or stolen exactly that part of 171 00:11:53.679 --> 00:11:57.879 the sunlight which would have given the two bright sodium lines. 172 00:11:59.159 --> 00:12:02.600 The spectrum of our means not two, but hundreds of 173 00:12:02.600 --> 00:12:06.960 bright lines in the solar spectrum. These hundreds of lines 174 00:12:07.000 --> 00:12:10.320 are dark because the iron gas in the atmosphere of 175 00:12:10.360 --> 00:12:13.440 the Sun has absorbed all that part of the light 176 00:12:13.559 --> 00:12:18.600 ray on its journey from the radiant photosphere. Therefore, when 177 00:12:18.679 --> 00:12:21.559 certain dark lines are apparent in the spectrum of the 178 00:12:21.639 --> 00:12:24.960 Sun or of a star, we know that the metal 179 00:12:25.000 --> 00:12:29.720 which always shows exactly corresponding bright lines is present in 180 00:12:29.759 --> 00:12:33.840 the atmosphere of that sun or star. By the same mode, 181 00:12:34.039 --> 00:12:37.519 the make of comets, of nebulae, and of other heavenly 182 00:12:37.559 --> 00:12:42.559 bodies can be tested and examined. This may give just 183 00:12:42.639 --> 00:12:45.720 a faint idea of the first principles of a new 184 00:12:45.840 --> 00:12:50.480 grand branch of astronomy, included under the head of spectrum analysis. 185 00:12:51.240 --> 00:12:54.679 The science is a science of itself, however, and one 186 00:12:54.840 --> 00:12:59.960 full of complexity. Chemistry and astronomy here walk hand in hand, 187 00:13:00.080 --> 00:13:04.879 and the spectroscope alone can decide whether any particular star 188 00:13:05.360 --> 00:13:09.480 is in fact a sun. If the rainbow tinted ribbon 189 00:13:09.519 --> 00:13:13.360 of light is there crossed by thin dark lines due 190 00:13:13.399 --> 00:13:16.799 to the stellar atmosphere through which each ray has passed 191 00:13:17.159 --> 00:13:21.240 after quitting the photosphere, then that star may be counted 192 00:13:21.279 --> 00:13:26.320 a true sun. Such stars constitute the majority among the 193 00:13:26.360 --> 00:13:31.279 hosts of Heaven, yet variety without limit is found. In 194 00:13:31.320 --> 00:13:34.399 one star, the light from the photosphere is almost lost, 195 00:13:34.919 --> 00:13:39.480 almost absorbed by the surrounding atmosphere. In another, the light 196 00:13:39.559 --> 00:13:43.720 of the atmosphere so overpowers that of the photosphere that 197 00:13:43.879 --> 00:13:47.320 only bright gas lines are seen in the spectroscope, the 198 00:13:47.399 --> 00:13:53.200 continuous color band being comparatively faint. Besides telling us of 199 00:13:53.240 --> 00:13:56.480 the make of the stars, the spectroscope also speaks to 200 00:13:56.600 --> 00:14:00.720 us of their motions. A very tiny shift movement of 201 00:14:00.759 --> 00:14:04.279 the little dark lines or bright lines to right or 202 00:14:04.399 --> 00:14:09.000 left is sufficient. From this can be calculated with it 203 00:14:09.080 --> 00:14:13.360 is believed astonishing exactness the rate at which a star 204 00:14:13.519 --> 00:14:17.440 is rushing towards us or rushing away from us. For 205 00:14:17.559 --> 00:14:20.600 if the star is nearing our earth, the light waves 206 00:14:20.639 --> 00:14:23.960 coming from him are pressed together, so to speak, hurrying 207 00:14:24.000 --> 00:14:27.879 one upon another, while if the star is retreating, the 208 00:14:27.960 --> 00:14:31.720 light waves are affected in a reverse manner, delayed or 209 00:14:31.759 --> 00:14:35.840 pulled apart, if such a term may be used. By 210 00:14:35.879 --> 00:14:40.039 this method, also stars are discovered so dim as to 211 00:14:40.080 --> 00:14:43.720 be not only utterly invisible to the naked eye, but 212 00:14:43.960 --> 00:14:50.120 undiscoverable by the telescope. End of Section twenty seven.