One model assumes that the planets move on some "circle on a circle" to get retrograde motion, the other shows that this would come naturally from mutually concentric orbits of different peiods.

Because the scale adopted was large, the terrestrial planets - Resurgam included - were crammed into the middle; a tight scribble of concentric orbits banded around the star Delta Pavonis.

We were opposite the middle of North America, which told me that Laz was a more than competent pilot; had we been in the usual twenty-four-hour orbit, concentric with Earth's equator, we would have been over the equator at ninety west, i.e., over the Galapagos Islands.

When Voyager 1 scanned the Solar System from beyond the outermost planet, it saw, just as Copernicus and Galileo had said we would, the Sun in the middle and the planets in concentric orbits about it.

Surrounding the rings, Earthbound observers understood were the concentric orbits of the five moons then known: Miranda, Ariel, Umbriel, Titania, and Oberon.

The outermost human scout vessels, which Abulurd had placed in concentric orbits farther and farther from the infested planet, came in at last, cutting off the robotic ship's escape and opening fire.

Like a densely packed school of sharks, circling and circling, the machine battleships cruised along in overlapping concentric orbits.

They're in two different orbits, mind you, concentric orbits, one almost two thousand miles outside the other.

A model of successive views of an outer planet as seen from an inner planet as they revolve in concentric orbits about a sun.