Many Skies: Alternative Histories of the Sun, Moon, Planets, and Stars

Chapter 6. We Are Alone

52 6 WE ARE ALONE The Sun was setting on that bleak November day. In another hour the sky would be dark. On overcast nights we could see a modicum of light from natural and artificial illumination from the ground, but on clear nights the world and the sky are totally dark. No moons or planets act to illuminate the night because none exist. Only the stars remain. On occasion the Aurora Borealis and Aurora Australis shine near the magnetic north and south poles, respectively, in our upper atmosphere. Our spacecraft venture only into inner-earth orbits since there is no need to go farther into the black void. Physics is a rich field but astronomy is not; even the word, along with its erstwhile soulmate, astrology, appeared rarely. Both words are based on astri, the Latin word for stars, but in this world there are no measures for the stars. Here we assume a solar system devoid of everything except the Earth and the Sun. No other planets move about in the sky and no moon accompanies our world because no Mars-sized blob of condensed matter crashed into the proto-Earth to wrench from it the material that later consolidated into our Moon. How likely is such an arrangement? I leave to those who work with models of newly formed planetary systems the question of whether a gas cloud can condense into a single star and a single planet with no significant residue left over. Now that dozens of large Jupiter-sized planets have been clamoring for our attention by tugging on the primary stars they are orbiting and pulling at them like a small dog on a leash, we find that most stars seem to be members of binaries or multiple star systems; it may be that such a lone planet circling a lone star may apply in fact to only a tiny minority of cases, if any. The sky would appear no different from the sky we see on many a clear night whenever the Moon is not above the horizon. Every night would appear the same except for the slow seasonal changes due to our revolution around the Sun; thus, the winter constellations would in time give way to those of spring and later the ones of summer and autumn. No visible planets would amble across the sky, but none are visible on many nights now as it is. But despite this mutual commonplace , we will find that the bunch of other planets formed along with the Earth and the Sun 4.6 billion years ago have enriched our lives in many ways. Perhaps the most significant difference occurs in a consideration of the history of science and ideas in general. For example, astrology might have been discarded centuries ago because it would at most be limited to the simplistic sun-sign variety, the kind that appears in most newspaper columns. No Saturn would be lurking in the seventh house to complicate the simple horoscope; no Jupiter would be in quadrature with Mercury, ever ready to forecast momentous events, good or evil. Astrology at this sparing level might never have attained its present high degree of popularity. However, charlatans would still be able to manipulate many other pseudosciences ready to fill its place; tea leaves, phrenology, and the tarot cards would still be available to attract the gullible and their money. The science in astronomy also takes a completely different turn. From classic times, when Pythagoras explained the nature of eclipses and shortly thereafter, Aristotle and Eudoxus imagined a solar system of interconnected shells accounting for each planet’s motions, the planets and the way they are seen to move became the principal medium in which modern science was born. Neither their geocentricity nor later the more complex cosmos of Ptolemy, nor the heliocentric planetary system introduced by Nicolaus Copernicus could be imagined. Whether the Earth or the Sun did the moving would remain a moot point until very late in the post-medieval world. Only when the aberration of starlight and the direct measure of stellar parallax could be mastered using the improved instrumentation in the eighteenth and nineteenth centuries could the problem be settled. The astronomical unit is by far the most important distance in the universe, since the measurements of distances to every object within or without the solar system, save only the Moon, all depend on its accuracy. Yet it could hardly be well determined even today, since...