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Kindle Notes & Highlights
by
Carl Sagan
The known is finite, the unknown infinite; intellectually we stand on an islet in the midst of an illimitable ocean of inexplicability. Our business in every generation is to reclaim a little more land. —T. H. Huxley, 1887
The dimensions of the Cosmos are so large that using familiar units of distance, such as meters or miles, chosen for their utility on Earth, would make little sense. Instead, we measure distance with the speed of light. In one second a beam of light travels 186,000 miles, nearly 300,000 kilometers or seven times around the Earth. In eight minutes it will travel from the Sun to the Earth. We can say the Sun is eight light-minutes away. In a year, it crosses nearly ten trillion kilometers, about six trillion miles, of intervening space. That unit of length, the distance light goes in a year, is
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If we were randomly inserted into the Cosmos, the chance that we would find ourselves on or near a planet would be less than one in a billion trillion trillion* (1033, a one followed by 33 zeroes).
A galaxy is composed of gas and dust and stars—billions upon billions of stars. Every star may be a sun to someone.
There are some hundred billion (1011) galaxies, each with, on the average, a hundred billion stars. In all the galaxies, there are perhaps as many planets as stars, 1011 × 1011 = 1022, ten billion trillion. In the face of such overpowering numbers, what is the likelihood that only one ordinary star, the Sun, is accompanied by an inhabited planet? Why should we, tucked away in some forgotten corner of the Cosmos, be so fortunate? To me, it seems far more likely that the universe is brimming over with life. But we humans do not yet know.
Blue stars are hot and young; yellow stars, conventional and middle-aged; red stars, often elderly and dying; and small white or black stars are in the final throes of death. The Milky Way contains some 400 billion stars of all sorts moving with a complex and orderly grace.
Each star system is an island in space, quarantined from its neighbors by the light-years.
Human beings, born ultimately of the stars and now for a while inhabiting a world called Earth, have begun their long voyage home.
