Sunday, December 11, 2016


from 1001 things everyone should know about science by james trefil

"the sun is a very ordinary star."

"it is likely that there is a black hole at the center of the galaxy. astronomers studying radiation coming from the center of our galaxy (in the constellation sagittarius) have come to the conclusion that something very strange is going on there. they see a large empty space in the center, free of gas but surrounded by swirling, chaotic threads of material. from the motion of this material, they conclude that there must be a massive object at the center of the galaxy -- several million times bigger than the sun. the best candidate for such an object would be a large black hole."

"859: the separation of charges in a thundercloud produces the lightning bolt. the large negative charge in the lower face of the clouds repels electrons from objects in the ground underneath it. the result is a 'shadow' of the cloud in the ground -- a region of positive charge. these charges follow along underneath the cloud, running up and down trees and buildings as they do so.

a lightning bolt begins when the charge in the cloud gets strong enough to ionize the air in its immediate vicinity. it opens a passage of ionized air several hundred feet long, called a 'leader.' because ionized air is a good conductor, the negative charge runs down into the leader. this process is repeated -- another leader is formed -- and the chain of leaders makes its way almost to the ground. about 100 feet above the ground, it is met by a leader formed by the positive charges coming up to meet it. the result of all this activity is a jagged path of conducting material between the negative charge in the clouds and the positive charge on the ground. with nothing to stop it, the positive charge runs up to the cloud, neutralizing the negative charges there. we perceive this motion of charge as a lightning stroke. the energy dissipated because of the resistance in the ionized path heats the air and pushes it away. the air then returns into this partial vacuum and creates a thunderclap."

"895: almost all the heavy elements in your body were made in supernovae somewhere. all elements heavier than iron, and most of the atoms of elements heavier than helium, are made in supernovae and then returned to the interstar medium when the supernova explodes. there they wait until they are taken up in the formation of a new star and (perhaps) planets. the sun and the earth were formed from this sort of enriched gas 4.6 billion years ago. the calcium in your bones, the iron in your blood, and the carbon in your tissues all got their start inside a star somewhere, and most likely inside a supernova."

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