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.