Cypher,
This is from the FAQ section of
Heavens-Above Home Page
Q.Why are satellites not visible in the middle of the night? A.Satellites are only visible when they are lit by the sun, but the observer on the ground is already in darkness. These conditions are met only when the sun is below the observer's horizon, but not too far down or the satellites themselves are also in the earth's shadow. So normally, satellites are only visible a few hours after sunset, or before sunrise. In the middle of the night the sun is simply too far below the horizon to light them. In summer however, especially at latitudes far north or south, the sun is never too far down, even at midnight, and satellites can be seen the whole night through.