EXPANDING UNIVERSE

For a long time, it was widely believed that the universe was static or stationary which however not true. Our universe has been expanding since the day it was created. Even great physicists like Einstein and Sir Isaac Newton believed that the universe was static. If our universe was static then our universe would have collapsed into a small ball due to gravity, as there would have been no force to retaliate the gravitational force. The discovery that the universe is expanding was made by no other than Edwin Hubble. He had no direct way to prove that the universe was expanding as he couldn't simply just measure the distance of other galaxies from us constantly as they were very far away and seemed to be fixed at one point. So he used indirect ways to prove it. The apparent brightness of a star depends on two factors how far it is from us and its luminosity. Conversely, if we knew the luminosity of stars in other galaxies we could work out their distance by measuring their apparent brightness. Hubble argued that certain types of stars always had the same luminosity. thus we could calculate the distance to that galaxy. if we could do this several times and our calculations always gave the same estimate we could be confident about our answer(he worked out distances of nine galaxies like this ). Hence this way he proved that our universe was expanding. 

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YOURS SARTHAK RAWAT AND PHEONIX(my super smart bird )