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cutaway diagram showing the earths interior as it would look if you cut intothe planet with a large knife and carefully withdrew a wedge representing about a quarter ofits bulk。
its hard to believe that there was ever a time when i had not seen such an illustrationbefore； but evidently i had not for i clearly remember being transfixed。 i suspect； in honesty；my initial interest was based on a private image of streams of unsuspecting eastboundmotorists in the american plains states plunging over the edge of a sudden 4；000…mile…highcliff running between central america and the north pole； but gradually my attention did turnin a more scholarly manner to the scientific import of the drawing and the realization that theearth consisted of discrete layers； ending in the center with a glowing sphere of iron andnickel； which was as hot as the surface of the sun； according to the caption； and i rememberthinking with real wonder： 〃how do they know that？〃i didnt doubt the correctness of the information for an instant…i still tend to trust thepronouncements of scientists in the way i trust those of surgeons； plumbers； and otherpossessors of arcane and privileged information…but i couldnt for the life of me conceive how any human mind could work out what spaces thousands of miles below us； that no eye hadever seen and no x ray could penetrate； could look like and be made of。 to me that was just amiracle。 that has been my position with science ever since。
excited； i took the book home that night and opened it before dinner…an action that i expectprompted my mother to feel my forehead and ask if i was all right…and； starting with the firstpage； i read。
and heres the thing。 it wasnt exciting at all。 it wasnt actually altogether prehensible。
above all； it didnt answer any of the questions that the illustration stirred up in a normalinquiring mind： how did we end up with a sun in the middle of our planet？ and if it isburning away down there； why isnt the ground under our feet hot to the touch？ and why isntthe rest of the interior melting…or is it？ and when the core at last burns itself out； will some ofthe earth slump into the void； leaving a giant sinkhole on the surface？ and how do you knowthis？ how did you figure it out？
but the author was strangely silent on such details…indeed； silent on everything butanticlines； synclines； axial faults； and the like。 it was as if he wanted to keep the good stuffsecret by making all of it soberly unfathomable。 as the years passed； i began to suspect thatthis was not altogether a private impulse。 there seemed to be a mystifying universalconspiracy among textbook authors to make certain the material they dealt with never strayedtoo near the realm of the mildly interesting and was always at least a longdistance phone callfrom the frankly interesting。
i now know that there is a happy abundance of science writers who pen the most lucid andthrilling prose…timothy ferris； richard fortey； and tim flannery are three that jump out froma single station of the alphabet （and thats not even to mention the late but godlike richardfeynman）…but sadly none of them wrote any textbook i ever used。 all mine were written bymen （it was always men） who held the interesting notion that everything became clear whenexpressed as a formula and the amusingly deluded belief that the children of america wouldappreciate having chapters end with a section of questions they could mull over in their owntime。 so i grew up convinced that science was supremely dull； but suspecting that it needntbe； and not really thinking about it at all if i could help it。 this； too； became my position for along time。
then much later…about four or five years ago…i was on a long flight across the pacific；staring idly out the window at moonlit ocean； when it occurred to me with a certainunfortable forcefulness that i didnt know the first thing about the only planet i was evergoing to live on。 i had no idea； for example； why the oceans were salty but the great lakeswerent。 didnt have the faintest idea。 i didnt know if the oceans were growing more saltywith time or less； and whether ocean salinity levels was something i should be concernedabout or not。 （i am very pleased to tell you that until the late 1970s scientists didnt know theanswers to these questions either。 they just didnt talk about it very audibly。）and ocean salinity of course represented only the merest sliver of my ignorance。 i didntknow what a proton was； or a protein； didnt know a quark from a quasar； didnt understandhow geologists could look at a layer of rock on a canyon wall and tell you how old it was；didnt know anything really。 i became gripped by a quiet； unwonted urge to know a littleabout these matters and to understand how people figured them out。 that to me remained thegreatest of all amazements…how scientists work things out。 how does anybody know howmuch the earth weighs or how old its rocks are or what really is way down there in thecenter？ how can they know how and when the universe started and what it was like when itdid？ how do they know what goes on inside an atom？ and how； e to that…or perhapsabove all…can scientists so often seem to know nearly everything but then still cant predict anearthquake or even tell us whether we should take an umbrella with us to the races nextwednesday？
so i decided that i would devote a portion of my life…three years； as it now turns out…toreading books and journals and finding saintly； patient experts prepared to answer a lot ofoutstandingly dumb questions。 the idea was to see if it isnt possible to understand andappreciate…marvel at； enjoy even…the wonder and acplishments of science at a level thatisnt too technical or demanding； but isnt entirely superficial either。
that was my idea and my hope； and that is what the book that follows is intended to be。
anyway； we have a great deal of ground to cover and much less than 650；000 hours in whichto do it； so lets begin。
PART I LOST IN THE COSMOS
？灏忚/t锛竧｜澶╁爞
they鈥檙e all in the same plane。
they鈥檙e all going around in the same direction。 。 。 。
it鈥檚 perfect； you know。
it鈥檚 gorgeous。
it鈥檚 almost uncanny。
…astronome