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.