ONE HUNDRED QUESTIONS AND ANSWERS ON “RECREATIONS IN ASTRONOMY,” CHAPTERS I TO VII, BOTH INCLUSIVE—CREATIVE PROCESSES, CREATIVE PROGRESS, ASTRONOMICAL INSTRUMENTS, CELESTIAL MEASUREMENTS; THE SUN; THE PLANETS, AS SEEN FROM SPACE; SHOOTING-STARS, METEORS, AND COMETS.

By ALBERT M. MARTIN, General Secretary C. L. S. C.

1. Q. What are the two laws of the attraction of gravitation? A. (1) Gravity is proportioned to the quantity of matter, and (2) the force of gravity varies as the square of the distance from the center of the attracting body.

2. Q. What is the original form of matter? A. Gas.

3. Q. What is inertia? A. If a body is at rest, inertia is that quality by which it will forever remain so, unless acted upon by some force from without; and if a body is in motion, it will continue on at the same speed, in a straight line, forever, unless it is quickened, retarded, or turned from its path by some other force.

4. Q. What is the result of the action of attraction and inertia upon two revolving bodies? A. They circle about each other as long as these forces endure.

5. Q. What would be the solution of the problem of a simple revolution of one world about another in a circular orbit? A. It would always be at the same distance from its center, and going with the same velocity.

6. Q. In the case of the moon, how many causes are there that interfere with such a simple orbit? A. Over sixty.

7. Q. What is heat? A. A mode of motion.

8. Q. Through what do all the light and heat of the sun that appear upon our earth come? A. Through space that is two hundred degrees below zero, and through utter darkness.

9. Q. At what velocity does light travel? A. One hundred and eighty-five thousand miles per second.

10. Q. What is the highest velocity we can give a rifle ball? A. Two thousand feet a second.

11. Q. How long does it take light to travel from the sun to the earth? A. About eight minutes.

12. Q. What is light? A. The result of undulations in ether.

13. Q. What are the different effects we call color? A. They are simply various velocities of vibration.

14. Q. How does sunlight melt ice? A. In the middle, bottom, and top at once.

15. Q. What is the effect of dark heat on ice? A. It only melts the surface.

16. Q. What can you say of the passage of the heat of the sun and the heat of a furnace or stove through glass? A. Nearly all the heat of the sun goes through glass without hindrance; only a small portion of the heat of a furnace or stove goes through the same substance.

17. Q. If our air were as pervious to the heat of the earth as it is to the heat of the sun, how cold would the temperature of the earth become every night? A. Two hundred degrees below zero.

18. Q. What is said of worlds so distant as to receive from the sun only a thousandth part of the heat we enjoy? A. They may have atmospheres that retain it all.

19. Q. What is probable as to the temperature of Mars? A. It is probable that Mars, that receives but one-quarter as much heat as the earth, has a temperature as high as ours.

20. Q. What two radically different kinds of telescopes are made? A. The refracting telescope, and the reflecting telescope.

21. Q. Why is the refracting telescope so called? A. Because it is dependent on the refraction of light through glass lenses.

22. Q. Why is the reflecting telescope so called? A. Because it acts by reflecting the light from a concave mirror.

23. Q. What is the loss of light in the use of each kind of telescope? A. In passing through glass lenses it is about two-tenths. By reflection it is often one-half.

24. Q. In view of this peculiarity, among others, what is held as to the comparative quality of the two kinds of telescopes? A. That a twenty-six inch refractor is fully equal to any six-foot reflector.

25. Q. What is the weight of the Lord Rosse reflecting telescope? A. It has a metallic mirror weighing six tons, and a tube forty feet long, which, with its appurtenances, weighs seven tons more.

26. Q. What is a spectrum? A. A collection of the colors which are dispersed by a prism from any given light.

27. Q. If the light is sunlight what is the spectrum called? A. A solar spectrum.

28. Q. What is a spectroscope? A. An instrument to see these spectra.

29. Q. What are some of the amazing discoveries made by the spectroscope within a few years? A. In chemistry it reveals substances never known before. It tells the chemical constitution of the sun, the movements taking place, the nature of comets, and nebulÆ.

30. Q. By the spectroscope what do we know of the atmospheres of some of the other planets? A. We know that the atmospheres of Venus and Mars are like our own, and that those of Jupiter and Saturn are very unlike.

31. Q. From what are all our standards of time taken? A. From the stars.

32. Q. From what are the positions of the stars reckoned? A. As so many degrees, minutes and seconds from each other, from the zenith, or from a given meridian, or from the equator.

33. Q. How far apart are the stars called the Pointers in the Great Bear? A. Five degrees.

34. Q. To mistake the breadth of a hair, seen at a distance of one hundred and twenty-five feet, would cause how much of an error in the measurement of the distance of the sun from the earth? A. Three millions of miles.

35. Q. By means of a microscope how many lines ruled on a glass plate are we able to count within an inch? A. One hundred and twelve thousand.

36. Q. What angle does the smallest object that can be seen by a keen eye make? A. An angle of forty seconds.

37. Q. By putting six microscopes on the scale of the telescope on a mural circle, what degree of exactness are we able to reach? A. An exactness of one-tenth of a second, or one-thirty-six hundredth of an inch.

38. Q. In astronomical work how small measurements of time are made? A. To the minute fractional parts of a second.

39. Q. What is the personal equation of an observer? A. The time that it takes him to observe a thing and record it, which is substracted from all his observations in order to get at the true time.

40. Q. What is the parallax of a body? A. The angle that would be made by two lines coming from that body to the two ends of any conventional base, as the semi-diameter of the earth.

41. Q. What is the parallax of the moon, and also of the sun, with the semi-equatorial diameter of the earth for a base? A. That of the moon 57 seconds, and that of the nun 8.85 seconds.

42. Q. Taking the diameter of the earth’s orbit, 184 millions of miles, as a base, what can you say of the parallax of the stars? A. They have no apparent parallax on so short a base.

43. Q. What does Prof. Airy say of the orbit of the earth as seen from the nearest star? A. It would be the same as a circle six-tenths of an inch in diameter, seen at the distance of a mile.

44. Q. In what way has the approximate distance of a few of the stars been determined? A. By comparisons of the near and far stars one with another.

45. Q. Which is the nearest star? A. The brightest star in Centaur, never visible in our northern latitudes, which has a parallax of about one second.

46. Q. Which is the next nearest star? A. No. 61 in the Swan, or 61 Cygni, having a parallax of thirty-four one-hundredths of a second.

47. Q. On how many stars have approximate measurements been made? A. About eighteen in all.

48. Q. How long does it take light, traveling at the rate of 185,000 miles a second, to come from the nearest star, Alpha Centauri, to the earth? A. Three and one-fourth years.

49. Q. How long does it take light to come from the Pole Star to the earth? A. Forty-five years.

50. Q. In naming these enormous distances what astronomical unit is used? A. The distance of the earth from the sun, ninety-two and a half millions of miles.

51. Q. In measuring the distance from Alpha Centauri, the nearest star, how many times would this unit be used? A. Two hundred and twenty-six thousand times.

52. Q. What is said of the stars being near or far according to their brightness? A. They are not near or far according to their brightness. 61 Cygni is a telescopic star, while Sirius, the brightest star in the heavens, is twice as far away from us.

53. Q. What is the zodiacal light? A. It is a dim, soft light, somewhat like the milky-way, seen on clear moonless nights in March or April, in the western sky soon after sunset, often reaching, well defined, to the Pleiades.

54. Q. What are the indications as to the cause of this light? A. That it is caused by a ring of small masses of meteoric matter surrounding the sun, revolving with it and reflecting its light, and extending beyond the earth’s orbit.

55. Q. As we approach nearer the sun what is the first material substance with which we meet? A. The corona.

56. Q. Describe the corona. A. It rises from one to three hundred thousand miles from the surface, and the appearance consists of reflected light sent to us from dust particles or meteoroids about the sun.

57. Q. What is the region of discontinuous flame below the corona called? A. The cromosphere.

58. Q. What are some of the materials composing the cromosphere? A. Hydrogen is the principal material of its upper part; iron, magnesium, and other metals, some of them as yet unknown on earth, in the denser parts below.

59. Q. When only are the corona and cromosphere visible? A. Only during total eclipses, or by the aid of the spectroscope.

60. Q. What is all that we ordinarily see with the eye or telescope of the sun? A. The shining surface called the photosphere on which the cromosphere rests.

61. Q. What is the diameter of the photosphere, or the visible and measurable part of the sun? A. Eight hundred and sixty thousand miles.

62. Q. How many globes like the earth would it require to measure the sun’s diameter? A. One hundred and eight.

63. Q. What is the volume of the sun as compared with that of the earth? A. It is 1,245,000 times greater.

64. Q. What is the density of the sun as compared with that of the earth? A. It is only one-fourth as great.

65. Q. What is the mass of the sun as compared with that of all the planets, asteroids, and satellites of the solar system put together? A. It is seven hundred times as great.

66. Q. What are some of the opinions as to the surface of the sun? A. That it is hot beyond all estimate is indubitable. Whether it is solid or gaseous we are not sure.

67. Q. What on the surface of the sun have been objects of earnest and almost hourly study on the part of eminent astronomers for years? A. The spots.

68. Q. To what must the speed of the orbital revolution of the planets be proportioned? A. To the distance from the sun.

69. Q. What is the orbital speed of Mercury, and what that of Neptune? A. That of Mercury is about twenty-nine and a half miles in a second, and that of Neptune about three and one-third miles a second, or nearly nine times as slow.

70. Q. How do the periods of the axial revolution, which determine the length of the day, vary with the four planets nearest the sun? A. They vary only half an hour from that of the earth.

71. Q. In what time do Jupiter and Saturn revolve? A. In ten and ten and a quarter hours respectively.

72. Q. What is the density of Jupiter and Saturn as compared with the earth? A. That of Jupiter is about one-fourth and that of Saturn is about one-eighth that of the earth.

73. Q. How much less is the polar diameter of Jupiter than the equatorial? A. Five thousand miles.

74. Q. If we represent the sun by a globe two feet in diameter, how could we represent the comparative size of the five planets nearest the sun? A. Vulcan and Mercury by mustard seeds, Venus and Earth by peas, and Mars by one half the size.

75. Q. How could the comparative size of the other planets be represented? A. Asteroids, by the motes in a sunbeam; Jupiter, by a small-sized orange; Saturn, by a smaller one; Uranus, by a cherry; and Neptune, by one a little larger.

76. Q. Applying the principle that attraction is in proportion to the mass, what would a man weighing one hundred and fifty pounds on the earth weigh on Jupiter, and what on Mars? A. On Jupiter he would weigh three hundred and ninety-six pounds, and on Mars only fifty-eight pounds.

77. Q. How are the seasons of the planets caused? A. By the inclination of its axis to the plane of its orbit.

78. Q. What is said of the day and night of Jupiter? A. The sun is always nearly over the equator of Jupiter, and every place has nearly its five hours day and five hours night.

79. Q. How do the seasons of Earth, Mars and Saturn compare? A. They are much alike, except in length.

80. Q. How long are Saturn’s seasons? A. Each is seven and a half years long. The alternate darkness and light at the poles is fifteen years long.

81. Q. In what form are the orbits of the planets? A. Not in the form of exact circles, but a little flattened into an ellipse, with the sun always in one of the foci.

82. Q. What is that point called where a planet is nearest the sun, and what where it is farthest from it? A. The point nearest the sun is called the perihelion, and the farthest point the aphelion.

83. Q. What is the plane of the ecliptic? A. It is the plane of the earth’s orbit extended to the stars.

84. Q. What is said of the densities, sizes, and relations of the collections of matter smaller than the planets, scattered through space in the solar system? A. They are of various densities, from a cloudlet of rarest gas to solid rock; of various sizes, from a grain’s weight to little worlds; of various relations to each other, from independent individuality to related streams millions of miles long.

85. Q. By what names are they known when they become visible? A. Shooting-stars, meteors, and comets.

86. Q. How far above the surface of the earth do shooting-stars appear and disappear? A. They appear about seventy-three miles above the earth, and disappear about twenty miles nearer the surface.

87. Q. What is their velocity? A. Their average velocity is thirty-five miles a second, and it sometimes rises to one hundred miles a second.

88. Q. What does Prof. Peirce state as the result of his investigation in regard to meteors? A. That the heat which the earth receives directly from meteors is the same in amount which it receives from the sun by radiation, and that the sun receives five-sixths of its heat from the meteors that fall upon it.

89. Q. When the bodies are large enough to bear the heat, and the unconsumed center comes to the earth, what are they called? A. Aerolites or air-stones.

90. Q. What is said of the distribution of these bodies through space? A. They are not evenly distributed through space. In some places they are gathered into systems which circle round the sun in orbits as certain as those of the planets.

91. Q. How many such systems of meteoric bodies has it been demonstrated that the earth encounters in a single year? A. More than one hundred.

92. Q. What are comets? A. They are clouds of gas or meteoric matter, or both, darting into the solar system from every side, at every plane of the ecliptic, becoming luminous with reflected light, passing the sun, and returning again to outer darkness.

93. Q. What appendage do comets usually have? A. A tail, which follows the comet to perihelion, and precedes it afterwards.

94. Q. What is the character of the orbits of some comets? A. Very enormously elongated. One end may lie inside the earth’s orbit, and the other end be as far beyond Neptune as that is from the sun.

95. Q. How many comets have been visible to the naked eye since the Christian era? A. Five hundred.

96. Q. How many have been seen by telescopes since their invention? A. Two hundred.

97. Q. How is the number of comets belonging to our solar system estimated by some authorities? A. By millions.

98. Q. What is the comet last seen in 1852, previously separated into two parts, called? A. Biela’s lost comet.

99. Q. How near did the great comet of 1843 pass to the sun? A. It passed nearer than any other known body. It almost grazed the sun.

100. Q. What was one of the most magnificent comets of modern times? A. Donati’s comet of 1858.