In the Preface, I gave my “short list” of the truly essential facts about astronomy and the nature of science. Now that you have spent many months studying astronomy, this list, which probably did not mean very much to you back then, will have assumed much more meaning. Here it is again.

Three BIG FACTS about the Universe

The Universe is very big

It is probably impossible to appreciate the immensity of the astronomical Universe. If we represent the entire Earth by a dot a mere 1/25th of an inch (1 millimeter) across, the Sun would by 40 feet (12.2 meters) away, and the nearest star a full 1840 miles (2961 kilometers) distant. Our Milky Way Galaxy would be an astonishing 46 million miles (about 74 million kilometers) in diameter. Beyond this lies the void of intergalactic space and untold billions of other galaxies. We have never found an end to these oceanic immensities. Indeed, the Universe might be infinite in extent.

The Universe is very old

It is also probably impossible to appreciate the immensity of the age ofthe cosmos. Our Earth is more than four billion years old: that is thousands of times longer than the span of time our human race has been in existence. If we shrink the lifetime of a person to a single minute, the Big Bang occurred nearly four centuries ago.

We are not the center of the Universe

Nothing about the Earth is unique. Our home planet lies in the outskirts of our Galaxy. We revolve about the Sun, which orbits about the Galaxy, which itself moves through space. Immense numbers of other planets revolve around their home stars.