What if Earth had several moons or massive rings like Saturn?  What if the Sun were but one star in a double-star or triple-star system?  What if Earth were the only planet circling the Sun?
These and other imaginative scenarios are the subject of Arthur Upgren's inventive book
Many Skies: Alternative Histories of the Sun, Moon, Planets, and Stars.
Although the night sky as we know it seems eternal and inevitable, Upgren reminds us that, just as easily, it could have been very different.
Had the solar sytem happened to be in the midst of a star cluster, we might have many more bright stars in the sky.  Yet had it been located beyond the edge of the Milky Way galaxy, we might have no stars at all.  If Venus or Mars had a moon as large as ours, we would be able to view it easily with the unaided eye.  Given these or other alternative skies, what might Ptolemy or Copernicus have concluded about the center of the solar sytem and the Sun?
This book not only examines the changes in science that these alternative solar, stellar, and galactic arrangements would have brought, it also explores the different theologies, astrologies, and methods of tracking time that would have developed to reflect them. Our perception of our surroundings, the number of gods we worship, the symbols we use in art and literature, even the way we form nations and empires are all closely tied to our particular (and accidental) placement in the universe.
Many Skies
, however, is not merely a fanciful play on what might have been.  Upgren also explores the actual ways that human interferences such as light pollution are changing the night sky.  Our atmosphere, he warns, will appear very different if we have belt of debris circling the globe and blotting out the stars, as will happen if advertisers one day pollute space with brilliant satellites displaying their products.
From fanciful to foreboding, the scenarios in
will both delight and inspire reflection, reminding us that ours is but one of many worldviews based on our experience of a universe that is as much a product of accident as it is of intention.