The Hidden Ocean
Right now, you are surrounded by water, even if you can't see it. This water exists as an invisible gas called 'water vapor.' We don't notice it until the air becomes 'saturated,' meaning the invisible sponge is full. The riddle of the morning dew is a story about what happens when the air is forced to 'squeeze' that sponge.
The Cold Surface Trick
Think about a cold glass of lemonade on a hot summer day. Within minutes, the outside of the glass is covered in droplets. That water didn't leak through the glass; it came from the air! When the warm air in the room touched the cold surface of the glass, it cooled down instantly. Since cold air can't hold as much water as warm air, it dumped its moisture right onto the glass.
Nighttime Cooling
During the day, the ground and the grass soak up heat from the Sun. But as soon as the Sun goes down, the Earth begins to radiate that heat back into space. Objects like grass, leaves, and car roofs cool down much faster than the air itself. By the early morning, the grass is often many degrees colder than the atmosphere surrounding it.