By day we looked up and it was blue, with the sun in it and, dimly, the moon. When the sun descended, blue became black, and the moon and stars were moving in it. We called it whatever we called it in our divers tongues. Sky. We see it still, but differently now because of what we have learned.

Some of us once saw the stars as holes in the sky where light came through. Some of us located sun, moon, stars and planets on several concentric spheres. The sun, we learned, does not revolve around the earth, nor does anything else except the moon. The sky is not an object and the blue is something that happens to the light. Now we know: moon around our earth, planets, asteroids, comets, etc. around our sun, stars around the galactic center, stars with planets in orbit, galaxies further than we could once imagine. We have not finished learning about these things; we are at the beginning of learning.

We began a little while ago to learn that the earth is indeed surrounded by concentric spheres, not blue or black: the ionosphere, parts of which reflect some radio waves, making them available beyond the line of sight; the ozone layer that keeps out harmful radiation, except what comes in through the holes; the magnetosphere with its radiation belts; the layers of the atmosphere, troposphere, stratosphere, mesosphere, thermosphere; and so on.

Some of us and some of our machines have penetrated and gone beyond earth's sky.

This is a metaphor for truth, and an example of it.