Astronomy
In the year 134 B.C., a temporary star blazed out in the constellation Scorpio. It was observed by a man of extraordinary genius, and furnished the incentive to one of his most memorable works. This was the construction, on essentially modern principles, of a catalogue of 1,08...
In the year 134 B.C., a temporary star blazed out in the constellation Scorpio. It was observed by a man of extraordinary genius, and furnished the incentive to one of his most...
2. CHAPTER II.On March 13, 1781, an event occurred without precedent in the history of astronomy. A new member of the sun’s immediate retinue was disclosed. A hard-worked music-teacher at Bat...
3. CHAPTER I.It is a common remark that we are creatures of circumstances, and in no sense is this truer than in its application to the conditions under which we view the heavenly bodies. At...
4. CHAPTER II.APPARENT MOVEMENTS OF THE SUN.—During any day on which we may observe the sun, it will be seen to rise at a certain place on the horizon, gradually ascend into the heavens to a...
5. CHAPTER III.TWO MEASUREMENTS REQUISITE.—In order to make a more precise study of the movements of the heavenly bodies, it is essential that we should have some very definite means of specif...
6. CHAPTER IV.EXACT SHAPE OF THE ORBIT.—It will be clear that if we made our annual journey in a circle we should always be at the same distance from the sun, and the apparent size of that lu...
7. CHAPTER V.SUN-DIAL TIME.—The changing directions of shadows thrown by the sun have been utilised from very remote periods for the measurement of time, the instrument usually employed bein...
8. CHAPTER VI.THE MOON’S REVOLUTION.—Apart from the changes in the appearance of the moon due to the ever-varying phases, the first fact which strikes the attentive observer is that the moon...
9. CHAPTER VII.APPARENT MOVEMENTS OF PLANETS.—It has already been pointed out that like the sun and moon, the planets also have an apparent movement with respect to the more distant stars. Mer...
10. CHAPTER VIII.ECLIPSES OF THE MOON.—As the various members of the solar system shine only by virtue of the light which they receive from the sun, they will cease to be visible if by any means...
11. CHAPTER IX.DETERMINATION OF LATITUDE.—In order that we may precisely define our situation upon the terrestrial sphere, we have seen that two measurements are necessary, namely, latitude an...
12. CHAPTER X.GEODESY.—We have already seen that the earth is a sphere, or of some form which differs but little from a sphere, and a rough method of determining its size, on this supposition...
13. CHAPTER XI.PARALLAX.—The problem of determining the distance of a heavenly body resolves itself into a measurement of its _parallax_, that is, of the apparent change of its position brough...
14. CHAPTER XII.MASS AND WEIGHT.—As a matter of daily experience, we know that a certain effort is required to prevent a body from falling to the ground, and the larger the bulk of any particul...
15. CHAPTER XIII.THE TIDES.—The familiar phenomena of the tides are of such importance to commerce in so many parts of the world that they have been carefully investigated from very early times....
16. CHAPTER XIV.GRADUATED CIRCLES.—Astronomy is essentially a science of precision, and the progress of our knowledge has to a large extent been dependent upon the increasing power of accuratel...
17. CHAPTER XV.THE REFRACTING TELESCOPE.—The function of a telescope is two-fold. First, to magnify the heavenly bodies, or, what comes to the same thing, to make them look as if they were nea...
18. CHAPTER XVI.THE MERIDIAN CIRCLE.—The accurate registration of the positions of the heavenly bodies is one of the most important functions of an astronomical observatory. When the apparent p...
19. CHAPTER XVII.So far we have been concerned with instruments which enable us to ascertain the positions, dimensions, and appearances of the various orders of heavenly bodies; but we can go fu...
20. CHAPTER I.The solar system consists of one supereminent body, with a train of miscellaneous attendants. By its immense gravitative power, their movements are so governed that they not onl...
21. CHAPTER II.The sun is an immense reservoir of radiant energy. For our daily uses we have no other store worth mentioning to draw upon, our fuel being the embalmed sun-heat of former ages;...
22. CHAPTER III.“What we ordinarily call the sun,” wrote the late Mr. Ranyard, “is only the bright spherical nucleus of a nebulous body.”[13] But it is only when the interposing moon cuts off t...
23. CHAPTER IV.The Interior Planets are those which revolve within the earth’s orbit. They are two in number—Mercury and Venus. Mercury, with a diameter of three thousand miles, is the smalles...
24. CHAPTER V.The earth occupies a critical position in the solar system. Its greater distance from the sun preserved it from the fate of Mercury and Venus. The influence of solar tidal frict...
25. CHAPTER VI.The furthest terrestrial planet from the sun is Mars, the “star of strength.” No other heavenly body, except the moon, is so well placed for observation from our position in spa...
26. CHAPTER VII.Between the orbits of Mars and Jupiter is interposed a huge gap. On one side of it lie the terrestrial planets; on the other, the “major planets”—orbs belonging to a different o...
27. CHAPTER VIII.Jupiter is by far the most important member of the solar family. The aggregate mass of all the other planets is only two-fifths of his, which 316 earths would be needed to count...
28. CHAPTER IX.Nearly twice as far from the sun as Jupiter revolves a planet, the spacious orbit of which was, until 1781, supposed to mark the uttermost boundary of the solar system. The mean...
29. CHAPTER X.The four giant planets, closely allied as they are, and strongly distinguished in physical constitution from the terrestrial planets, divide again of themselves into two sub-gro...
30. CHAPTER XI.In the fourth year of the 101st Olympiad (373 B.C.), the Greeks were startled by a celestial portent. They did not, at that time, draw fine distinctions, and posterity would hav...
31. CHAPTER XII.Comets reflect sunlight, and also emit light of their own. But the combination was scarcely thought of as possible until the spectroscope gave its verdict. The first analysis of...
32. CHAPTER XIII.At Madrid, on the morning of February 10, 1896, the sunshine was at 9.30 overpowered by a vivid flash of bluish light, succeeded by a violent explosion. Much glass was broken, a...
33. CHAPTER I.The study of the sidereal heavens is one of surpassing interest, and tends to raise our minds above the sordid things of time and the petty affairs of the little planet on which...
34. CHAPTER II.Many of the stars when examined with a good telescope are seen to be double, some triple, and a few quadruple, and even multiple. These when viewed with the naked eye, or even a...
35. CHAPTER III.The determination of the distances of the stars from the earth has always formed a subject of great interest to astronomers. The earlier observers appear to have thought that th...
36. CHAPTER IV.Double and multiple stars may be either optical or real. Optical double stars are those in which the component stars are merely apparently close together, owing to their being s...
37. CHAPTER V.To ordinary observers, the light of the stars seems to be constant. Even to those who are familiar with the constellations, the stars appear to maintain their relative brillianc...
38. Chapter III., the motion of a star in the line of sight can beascertained by measuring displacements in the positions of the spectral lines. Now, if the diminution in Algol’s light is due to a dark body revolving round it, and periodically...
39. CHAPTER VI.Clusters of stars and nebulæ are frequently classed together in one group. But this is incorrect. The term nebulæ should be restricted to those objects which the spectroscope sh...
40. CHAPTER VII.The construction of the visible universe is one of great interest, but of considerable difficulty. If we reflect that in viewing the starry heavens we are placed at the centre o...