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  • Print publication year: 2014
  • Online publication date: February 2014

Preface

Summary

Our Sun is a fairly ordinary star, a bit brighter than most but not exceptionally so. There are many stars much bigger and brighter, while most stars are smaller and fainter. The Sun is not an especially variable or active star, and it has no enormous chemical or magnetic peculiarities. It is not a very young star, nor is it old and nearing the end of its life. It is, in short, truly exceptional in only one way: it is very close to the Earth – in fact, at just the right distance to make life as we know it possible.

Most of us do not worship the Sun as did many in ancient civilizations, but we certainly should not take for granted the light and heat that it provides. Left to itself, the Earth would be a fantastically frigid rock at near absolute-zero temperature. If the Sun had been slightly more massive, its high temperature would have made the Earth's surface hot enough to melt lead. A smaller Sun would have left the Earth unbearably cold and possibly subject to high levels of radiation, since smaller stars tend to have higher levels of activity, giving off devastating ultraviolet and x-rays. Distance also matters. Had the Earth been closer, we might be as infernally hot as Venus; farther away and we might have been as cold and arid as Mars. We are in the position of Goldilocks, living at just the right distance from a just-right star.