The above distances are merely approximate and are subject to further
revision. A "light-year" is the distance that light, travelling at the
rate of 186,000 miles per second, would cover in one year.]
In this simple outline we have not touched on some of the more debatable
questions that engage the attention of modern astronomers. Many of these
questions have not yet passed the controversial stage; out of these will
emerge the astronomy of the future. But we have seen enough to convince
us that, whatever advances the future holds in store, the science of the
heavens constitutes one of the most important stones in the wonderful
fabric of human knowledge.