unimaginably remote galaxy, blazing as bright as hundreds of billions of stars and creating a fireball that expands and cools for months. We're lucky that they rarely strike close to home. The last supernova in our own galaxy exploded in 1604, rivaling Jupiter's brightness in the night sky and deeply impressing Johannes Kepler, the pioneering astronomer. A nearby supernova--within a few light-years--would bathe the Earth in lethal radiation. Yet the legacy of supernovas is as close as our own bodies. The carbon in our cells, the oxygen in the air, the silicon in rocks and computer chips, the iron in our blood and our machines--just about every atom heavier than hydrogen and helium--was forged inside ancient stars and strewn across the universe when they exploded billions of years ago. Eager to understand our origins and, in some cases, simply wild about things that go bang, astronomers have been struggling for
mille käigus tekib plii. Kosmoses toimub kaks protsessi - Aeglane (slow-s) ja kiire (rapid-r). Mõlemad protsessid toimuvad tähtede sees või nende ümber. Aeglases (s) protsessis toimub plii loomine aastate või sajandite vältel. Pika aja jooksul muutuvad vähem stabiilsed tuumad beetakiirguse all stabiilseteks tuumadeks. Beetakiirguse abil moodustub plii isotoop massiga 204, 205, jne. Kiires (r) protsessis toimub plii loomine enne tuuma langundamist. Selliseid tekkeid saab juhtuda Supernovas või kahe neutron tähe ühendumisel. Kiire protsess ei võimalda nii palju plii tegemist, kui aeglane protsess, sest kiire protsess lõpeb, kui tuumas on 126 neutroni ja rohkem juurde ei mahu. Maal on haruldane leida puhast pliid. Plii on tekkinud teiste metallide mineraalidest. Plii maake võib leiduda hüdrotermilistes veenides ja vulkaanides. Maa elu jooksul on jäänud algusest saadik plii mineraale maakoorde, mida on tänapäeval võimalik lihtsalt kätte saada. (wikipedia.ee)
Such occurrences made lasting impressions on all men, whether scientist or not. After all, this was an age in which men believed their fate to be written in the stars and now those stars were changing. What Brahe and Kepler had seen were supernovas, the explosions of old stars. Kepler, even more than Copernicus, was literally carried away by the strange relationship between numbers and the properties of the natural world. In his books, one theme is presented repeatedly: "Nature loves simplicity." From his friend Brahe, Kepler learned that it was necessary to take more accurate measurements while observing the movement of the heavenly bodies. In the end, Kepler determined the three laws of
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