Jim asks: "Knowing that water and moisture should always weigh the same, why do clouds form at different altitudes? What makes a cirrus cloud different from a stratus cloud?"
Clouds are grouped into three different levels in the sky based on altitude.
Low-level clouds, which include cumulus and stratus clouds, are 6,500 feet or below.
Mid-level clouds are between 6,500 and 23,000 feet.
High-level clouds, like cirrus clouds, are between 16,500 and 45,000 feet high.
As for stratus clouds and cirrus clouds, they're both one of three basic shapes of clouds.
Stratus is Latin for "layer". Those clouds form in layers and often cover the entire sky. They're much wider than they are thick, and they kind of look like a blanket or a mattress.
Another way to describe the way they look is a layer of fog that never reaches the ground. In fact, fog that lifts from the ground is actually a layer of low stratus clouds.
Cirrus is Latin for "curl" because those are clouds of wispy curls. Some people think they look like a child's hair.
Those clouds usually form about 18,000 feet and are thin because they form in higher levels of atmosphere where little water vapor is present.
The third type of cloud, cumulus, is Latin for "heap". They're basically heaps of separated cloud masses. They have flat bottoms and cauliflower tops.