This week's question comes from Morning Brief reader Brenda: "Why don’t clouds just disperse if they are water vapor? Why do clouds have edges and maintain a semisolid appearance?"

A fun question to think about, actually. So the clarification comes from the fact that clouds are not actually made of water vapor.

While yes, water vapor is quite plentiful in the atmosphere, clouds are formed when air cannot hold any more water vapor, so it actually condenses and cools into tiny water droplets. Lots and lots of tiny, TINY water droplets. Like 0.02 millimeters small. For reference, a credit card is about 1 millimeter thick.

Particles this small are fascinating to me because they are able to be suspended in midair. Also fun to think about is that clouds are constantly shifting and changing. Tiny liquid water droplets may evaporate again as new water vapor cools and condenses, replacing evaporated water droplets. It is all so amazing.

These water droplets can collide and smash into each other, growing in size. Eventually, they get so big that they fall as rain. Should enough of that happen, the cloud will begin to fall apart and disperse. Another way to make a cloud disperse is to increase the temperature. Warmer air can hold more water vapor, so if you heat the air up, liquid water will evaporate back into water vapor. At least until you cool the air back down and it can't hold more water. This pattern is ongoing constantly.

You can also add dry air into a cloud. When you do this, it allows for more evaporation because the dry air pulls the air parcel away from the saturation point the air needs to be at to form clouds. That point is called the dew point, and if you add dry air, you end up un-saturating the air.

So now, why do clouds have edges?

Well, it is all about that saturation point, which is fluid and dynamic. Certain parts of the atmosphere have different saturation points, so a big parcel of air may be hitting saturation points in one area and not in another. The edge of the cloud serves as a boundary between saturation and unsaturation. In the unsaturated area, you have invisible water vapor. But, on the saturated side, you have tiny water droplets — clouds. This is why you can see clouds grow and shrink before your eyes. The atmosphere is dynamic and is bringing outside factors to a cloud constantly.

Also, we have to think about how many water droplets are in the cloud. The thicker the cloud, say a puffy cumulus cloud, the more droplets. These droplets are scattering incoming light, which is what makes them look so well defined.