The Highest Altitude Cloud: Cirrus

Cirrus clouds are the type of clouds that form at the highest altitudes in the sky. These clouds are thin, wispy, and often have a feathery appearance. They are composed of ice crystals and can be found at altitudes of around 20,000 feet (6,000 meters) to over 40,000 feet (12,000 meters) above the Earth's surface.

Explanation:
To understand why cirrus clouds form at higher altitudes, it is important to know how clouds are formed in the first place. Clouds are formed when moist air rises and cools, causing the water vapor in the air to condense into tiny droplets or ice crystals. The altitude at which this condensation occurs determines the type of cloud that forms.

1. Cirrus Clouds:
Cirrus clouds form at high altitudes, usually above 20,000 feet. They are composed of ice crystals and are thin and wispy in appearance. Cirrus clouds are often seen as white, delicate strands or feathery patches in the sky. They are commonly referred to as "mare's tails" due to their resemblance to the tail of a horse.

2. Stratus Clouds:
Stratus clouds, on the other hand, form at lower altitudes. They are flat, featureless clouds that cover the entire sky like a blanket. Stratus clouds are usually gray or white and can bring light rain or drizzle. They are often associated with stable weather conditions.

3. Nimbus Clouds:
Nimbus clouds, also known as cumulonimbus clouds, are massive and vertically developed clouds that can extend through a wide range of altitudes. They are associated with thunderstorms and can reach heights of up to 50,000 feet. Nimbus clouds are characterized by their anvil-shaped tops and can produce heavy rain, lightning, and even tornadoes.

4. Cumulus Clouds:
Cumulus clouds are large, fluffy clouds with a rounded shape. They typically form at lower altitudes and are often associated with fair weather. Cumulus clouds can grow vertically and develop into cumulonimbus clouds, which are associated with thunderstorms.

Conclusion:
In summary, cirrus clouds are the highest altitude clouds in the sky. They form at altitudes above 20,000 feet and are composed of ice crystals. Cirrus clouds have a thin, wispy appearance and are often seen as delicate strands or feathery patches in the sky.