By now you have probably begun to appreciate that the Universe is far larger than you had previously imagined. This is not to be unexpected. Unexpected were the breakthroughs made in the early 20th century into understanding how the Universe came to exist, and what it will look like in the future. The Universe consists of billions of galaxies. Each galaxy containing 100s or 1000s of millions of stars. Stars can be seen because they emit light (and other electro-magnetic (EM) radiation). All EM radiation travels at the speed of light.
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