听力原文： There is probably nothing more mysterious and wonderful-looking in the sky than the Milky Way, stretching like a band of jewels from one end of the sky to the other. Long, long ago, when people gazed at this sight, they were filled with wonder just as you are today. But since they didn't know what it was, they made up all sorts of strange and beautiful conjectures of the Milky Way. For example, in early Christian times, people thought it was a way along which the servants of God went up to heaven. Some imagined it was an opening in the heaven, so that we here on earth could have a glance of the magnificent inside. Knowing the facts about the Milky Way, as we do today, doesn't take away any of the wonder of it. The facts are just as amazing as any 'made-up' idea! Our galaxy is roughly like a watch, round and flat. If you could get above it and look down on it, it would look like a very large watch. But we are inside the galaxy, and when we look up we are looking towards the edge from inside the 'watch'. So we' see that edge around us. And since there are millions of stars in it, they appear to us as the Milky Way. Do you know that there are at least 3,000,000,000 stars in the galaxy? And here is an idea of its size. It takes eight minutes for light from the sun to reach the earth. For light from the middle point of the galaxy to reach the sun, it takes about 27,000 years! The galaxy turns about its center like a wheel. From our position in it, it takes about 200,000,000 years just to make one round. Long, long ago, people didn't know what the Milky Way was, so they explained it ______.