Did you not consider (the work of) your Fosterer, how He stretches the shade (which ultimately ends in night)? And had He willed he could have made it stationary. Then We have made the sun its guide,
The shadows depend on the position of the sun, in the morning and evening they arelong. Night is actually the shadow of the earth which is withdrawn at day time when the earth does not cover the sun. The force which counter acts gravity is consciousness or being awake. The moment we lose consciousness we fall down. At night the gravitational pull of the earth and the sun are on the same side with respect to us, this increased gravity might be helping us in falling asleep. In the morning these two pulls are on the opposite sides and they might be helping us in keeping awake or being conscious. It is probably by this method Allah (SWT) takes away the soul or consciousness during sleep 39:42.