Other Worlds | Page 2

and spectroscopic revelations--Changes of opinion--Desirability of a popular presentation of the latest facts--The natural tendency to regard other planets as habitable--Some of the conditions and limitations of the problem--The solar system viewed from outer space--The resemblances and contrasts of its various planets--Three planetary groups recognized--The family character of the solar system
CHAPTER II
MERCURY, A WORLD OF TWO FACES AND MANY CONTRASTS 18
Grotesqueness of Mercury considered as a world--Its dimensions, mass, and movements--The question of an atmosphere--Mercury's visibility from the earth--Its eccentric orbit, and rapid changes of distance from the sun--Momentous consequences of these peculiarities--A virtual fall of fourteen million miles toward the sun in six weeks--The tremendous heat poured upon Mercury and its great variations--The little planet's singular manner of rotation on its axis--Schiaparelli's astonishing discovery--A day side and a night side--Interesting effects of libration--The heavens as viewed from Mercury--Can it support life?
CHAPTER III
VENUS, THE TWIN OF THE EARTH 46
A planet that matches ours in size--Its beauty in the sky--Remarkable circularity of its orbit--Probable absence of seasons and stable conditions of temperature and weather on Venus--Its dense and abundant atmosphere--Seeing the atmosphere of Venus from the earth--Is the real face of the planet hidden under an atmospheric veil?--Conditions of habitability--All planetary life need not be of the terrestrial type--The limit fixed by destructive temperature--Importance of air and water in the problem--Reasons why Venus may be a more agreeable abode than the earth--Splendor of our globe as seen from Venus--What astronomers on Venus might learn about the earth--A serious question raised--Does Venus, like Mercury, rotate but once in the course of a revolution about the sun?--Reasons for and against that view
CHAPTER IV
MARS, A WORLD MORE ADVANCED THAN OURS 85
Resemblances between Mars and the earth--Its seasons and its white polar caps--Peculiar surface markings--Schiaparelli's discovery of the canals--His description of their appearance and of their duplication--Influence of the seasons on the aspect of the canals--What are the canals?--Mr. Lowell's observations--The theory of irrigation--How the inhabitants of Mars are supposed to have taken advantage of the annual accession of water supplied by the melting of the polar caps--Wonderful details shown in charts of Mars--Curious effects that may follow from the small force of gravity on Mars--Imaginary giants--Reasons for thinking that Mars may be, in an evolutionary sense, older than the earth--Speculations about interplanetary signals from Mars, and their origin--Mars's atmosphere--The question of water--The problem of temperature--Eccentricities of Mars's moons
CHAPTER V
THE ASTEROIDS, A FAMILY OF DWARF WORLDS 129
Only four asteroids large enough to be measured--Remarkable differences in their brightness irrespective of size--Their widely scattered and intermixed orbits--Eccentric orbit of Eros--the nearest celestial body to the earth except the moon--Its existence recorded by photography before it was discovered--Its great and rapid fluctuations in light, and the curious hypotheses based upon them--Is it a fragment of an exploded planet?--The startling theory of Olbers as to the origin of the asteroids revived--Curious results of the slight force of gravity on an asteroid--An imaginary visit to a world only twelve miles in diameter
CHAPTER VI
JUPITER, THE GREATEST OF KNOWN WORLDS 160
Jupiter compared with our globe--His swift rotation on his axis--Remarkable lack of density--The force of gravity on Jupiter--Wonderful clouds--Strange phenomena of the great belts--Brilliant display of colors--The great red spot and the many theories it has given rise to--Curious facts about the varying rates of rotation of the huge planet's surface--The theory of a hidden world in Jupiter--When Jupiter was a companion star to the sun--The miracle of world-making before our eyes--Are Jupiter's satellites habitable?--Magnificent spectacles in the Jovian system
CHAPTER VII
SATURN, A PRODIGY AMONG PLANETS 185
The wonder of the great rings--Saturn's great distance and long year--The least dense of all the planets--It would float in water--What kind of a world is it?--Sir Humphry Davy's imaginary inhabitants of Saturn--Facts about the rings, which are a phenomenon unparalleled in the visible universe--The surprising nature of the rings, as revealed by mathematics and the spectroscope--The question of their origin and ultimate fate--Dr. Dick's idea of their habitability--Swedenborg's curious description of the appearance of the rings from Saturn--Is Saturn a globe of vapor, or of dust?--The nine satellites and "Roche's limit"--The play of spectacular shadows in the Saturnian system--Uranus and Neptune--Is there a yet undiscovered planet greater than Jupiter?
CHAPTER VIII
THE MOON, CHILD OF THE EARTH AND THE SUN 212
The moon a favorite subject for intellectual speculation--Its nearness to the earth graphically illustrated--Ideas of the ancients--Galileo's discoveries--What first raised a serious question as to its habitability--Singularity of the moon's motions--Appearance of its surface to the naked eye and with the telescope--The "seas" and the wonderful mountains and craters--A terrible abyss described--Tycho's mysterious rays--Difference between lunar and terrestrial volcanoes--Mountain-ringed valleys--Gigantic cracks in the lunar globe--Slight force of gravity of the moon and some interesting deductions--The moon a world of giantism--What kind of atmospheric gases can the moon contain--The question of water and of former oceans--The great volcanic