The cylinder containing the orbits of the stars is almost as much a symbol as the figure of Necessity turning the spindle;--for the outermost rim is the sphere of the fixed stars, and nothing is said about the intervals of space which divide the paths of the stars in the heavens.

The description is both a picture and an orrery, and therefore is necessarily inconsistent with itself.

The column of light is not the Milky Way--which is neither straight, nor like a rainbow--but the imaginary axis of the earth.

This is compared to the rainbow in respect not of form but of colour, and not to the undergirders of a trireme, but to the straight rope running from prow to stern in which the undergirders meet.
The orrery or picture of the heavens given in the Republic differs in its mode of representation from the circles of the same and of the other in the Timaeus.

In both the fixed stars are distinguished from the planets, and they move in orbits without them, although in an opposite direction: in the Republic as in the Timaeus they are all moving round the axis of the world.