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138 BCE
The Big Bang
The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today. -
Period: 138 BCE to
Big history
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136 BCE
Stars Light Up
Stars shine because they are extremely hot (which is why fire gives off light — because it is hot). The source of their energy is nuclear reactions going on deep inside the stars. In most stars, like our sun, hydrogen is being converted into helium, a process which gives off energy that heats the star.
