Our astronomer writes: In his book Wind, Sand and Stars, Antoine de Saint Exupéry tells the story of a group of Bedouin from the Sahara brought to metropolitan France. This was in the days of the French colonies in North Africa, and the intent was to impress them with the greatness of the civilization of Europe (or at least its power) so they would stop fighting against it. On their return, they said Paris, iron bridges, locomotives, everything was “very big.” They’d learned that Frenchmen seemed to be satisfied by the phrase and used it to buy some peace. In fact they did not comprehend what their guides had tried to show them.

I find that, in explaining astronomy to the public (including students in introductory classes) there is a temptation to play to the “ooh and ahh factor,” to try to impress one’s audience with big numbers to show how different it is from normal experience. (Sometimes there is the unspoken subtext: “Look at me, how good I am to be able to work with huge numbers!”) But if we are not very careful we may, in the end, only leave the vague impression that astronomy is “very big.”

Well, the universe is a big place. But we’re not going to walk there, so there is little point in pacing off its distances. The point is to use numbers the way scientists do, to get a grasp of things that are too big, small, long or strange to understand without them.

Let’s look at one example. The Sun is about 25,000 light-years from the center of the Milky Way Galaxy, an unimaginably far distance, about which it is moving in an approximately circular orbit at 220 kilometers per second, an unimaginably fast speed. Even at this speed one orbit takes some 220 million years, an unimaginably long time. The Sun, a G-type star, is about 5 billion years old, even more unimaginable (if there are degrees of impossibility); a much bigger and brighter O-type star can live for maybe 6 million years before exploding in a supernova. Even this last, smallest number is many times the whole period homo sapiens has been around as a species, much less any particular member of it. We have here a stack of impossibly big numbers.

To make sense of this, take hold of that 220 million years that the Sun takes to circle the Galaxy. It is now our standard of time. An O-type star is a very short-lived thing: it will hardly complete a few percent of one orbit before exploding. If the orbit is the face of an analog clock, the star will not quite go from noon to 12:02. The Sun, by contrast, has made about 23 orbits already, and should make another 23 before transforming itself into a Red Giant.

Similarly unimaginable numbers occur throughout physics, chemistry and related sciences.  I will not try to speak for biology, but scientists there must face a similar tension: the tempation to emphasize the strange as opposed to making it something to understand.

For the quantitative sciences, let numbers be a tool for gasping the universe, rather than a way of convincing our audience only that it’s “very big.”