These penumbras may not be perceptible, but they affect the appearance of the shadows.

For instance, the shadow of the fourth is perceptibly larger but less black than that of the third, though the third is the larger satellite.
In transit the first satellite moves fastest, the fourth slowest, the others in their order.

The shadow moves just as fast (appreciably) as the satellite it belongs to.

Sometimes the shadow of the satellite may be seen to overtake (apparently) the disc of another.

In such a case the shadow does not pass over the disc, but the disc conceals the shadow.
This is explained by the fact that the shadow, if visible throughout its length, would be a line reaching slantwise from the satellite it belongs to, and the end of the shadow (that is, the point where it meets the disc) is _not_ the point where the shadow crosses the orbit of any inner satellite.