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The Earth is a planet. It spins once a day and circles the Sun once a year, as the other planets do, with the Sun near the center of it all.

If the air carried them along, they would never seem to move at all. But we see them move in every direction.

The air might turn with the Earth and carry the clouds and the birds along, so they wouldn’t be left behind.

If the Earth spun once a day from west to east, it would outrun everything not standing on it. Clouds, birds, and anything thrown would always seem to drift westward, and we would never see them move east.

Each planet rides on a small circle, an epicycle, whose center travels along a larger one around the Earth. On the near side of its epicycle, the planet moves against the larger circle’s motion, so it seems to drift backward.

Every so often, a planet seems to stop, drift backward among the stars for weeks, and then move on. A planet that simply circled the Earth would never do that.

The Earth stands still at the center of the universe. The Moon, the Sun, and the planets circle it.

The stars are so far away that, next to their distance, the Earth’s orbit is like a point. Their shift is far too small to see.

If the Earth circled the Sun, we would see the stars from different places over the year, so they would seem to shift back and forth. They don’t.

The Sun and the stars stand still. The Earth circles the Sun, which lies in the middle of its orbit, and spins as it goes.