30
The Sky of the Satellites

Thanks to the Voyager space probes we have learned a great deal about the four large Galilean satellites * of Jupiter: the volcanoes of Io, the cracked glacier that covers Europa, the frozen craters of Ganymede and Callisto.

Yet if we could imagine ourselves on the surface of any of these worlds and somehow protected from the harsh conditions, it would probably not be the surfaces that would hold our attention most, not the volcanoes, not the craters, not the cracked glaciers. It would be the skies.

Consider Callisto, the farthest of the Galileans, 1,171,000 miles from Jupiter's center.Thanks to Jupiter's tidal effect, Callisto, like the other Galileans, faces one side always to Jupiter, as our moon faces one side always to us.This means that Callisto rotates on its axis, relative to the universe generally, in the same time it revolves about Jupiter—once in 16.69 days.

Standing on Callisto, we would see the sun make one complete circle in that time, which means it would move considerably more slowly in Callisto's sky than in our own.On Callisto, the time from sunrise to sunset would be some 200 hours rather than the average of 12 hours that the sun stays in Earth's sky.

The three Galilean satellites that are closer to Jupiter than Callisto is revolve about Jupiter more quickly, hence rotate more quickly, and therefore see the sun move more rapidly across the sky.On Ganymede, the sun moves from rising to setting in 84 hours; on Europa, in 42.7 hours; on

____________________
*
They were first seen by Galileo in 1610.

-151-

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The Roving Mind
Table of contents

Table of contents

  • The Roving Mind *
  • Contents vii
  • Foreword Isaac Asimov: Science Popularizer, Skeptic, and Rationalist xi
  • A Celebration of Isaac Asimov — a Man for the Universe xv
  • Introduction 1
  • Part I the Religious Radicals *
  • 1: The Army of the Night *
  • 3: The Reagan Doctrine 20
  • 4: The Blind Who Would Lead 24
  • 5: Creeping Censorship 27
  • 6: Losing the Debate 29
  • Part II Other Aberrations 30
  • 7: The Harvest of Intelligence *
  • 8: That Old-Time Violence 37
  • 9: Little Green Men or Not? 40
  • 10: Don'T You Believe? 43
  • 11: Open Mind? 47
  • 12: The Role of the Heretic 49
  • Part III Population *
  • 13: The Good Earth is Dying *
  • 14: The Price of Survival 66
  • 15: Letter to a Newborn Child 72
  • Part IV Science: Opinion 74
  • 16: Technophobia *
  • 17: What Have You Done for Us Lately? 84
  • 18: Speculation 88
  • 19: Is It Wise for Us to Contact Advanced Civilizations? 92
  • 20: Pure and Impure 97
  • 21: Do We Regulate Science? 104
  • 22: For Public Understanding of Science 107
  • 23: Science Corps 110
  • 24: Science and Beauty 113
  • 25: Art and Science 116
  • 26: The Fascination of Science 120
  • 27: Sherlock Holmes as Chemist 127
  • Part V Science: Explanation 132
  • 28: The Global Jigsaw *
  • 29: The Inconstant Sun 139
  • 30: The Sky of the Satellites 151
  • 31: The Surprises of Pluto 157
  • 32: Neutron Stars 160
  • 33: Black Holes 162
  • 34: Faster Than Light 165
  • 35: Hyperspace 169
  • 36: Beyond the Universe 175
  • 37: Life on Earth 183
  • Part VI the Future 188
  • 38: Transportation and the Future *
  • 39: The Corporation of the Future 200
  • 40: The Future of Collecting 208
  • 41: The Computerized World 214
  • 42: The Individualism to Come 228
  • 43: The Coming Age of Age 237
  • 44: The Decade of Decision 244
  • 45: Do You Want to Be Cloned? 251
  • 46: The Hotel of the Future 256
  • 47: The Future of Plants 262
  • 48: Bacterial Engineering 266
  • 49: Flying in Time to Come 272
  • 50: The Ultimate in Communication 278
  • 51: His Own Particular Drummer 285
  • 52: The Future of Exploration 295
  • 53: Homo Obsoletus? 300
  • 54: Volatiles for the Life on Luna 307
  • 55: Touring the Moon 312
  • 56: Life on a Space Settlement 317
  • 57: The Payoff in Space 324
  • Part VII Personal *
  • 58: I Am a Signpost *
  • 59: The Word-Processor and I 334
  • 60: A Question of Speed 337
  • 61: A Question of Spelling 340
  • 62: My Father 344
  • Acknowledgments 348
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