The Earth is really, really old. Over 4 1/2 billion years old, in fact. How do we begin to comprehend a number that large? It helps to put it on a more fathomable scale. Watch to see where Earth's ...

The dots moving across the right side of the animation show how quickly each object travels 150 kilometers. As you can see, Earth's rotation is relatively slow, whereas the Milky Way is barreling ...