Cirrusly happy birthday original pen and ink and watercolour illustration by Rosie Brooks

Cirrus clouds are a type of high-altitude cloud that form at an altitude of 20,000 feet (6,000 meters) or higher. They are thin, wispy clouds that are composed of ice crystals and have a feathery appearance. Cirrus clouds are typically white or light gray in color and often form in long, streaky formations that stretch across the sky.

Cirrus clouds are formed when moist air is lifted to high altitudes, where it encounters cold temperatures and freezes into ice crystals. These ice crystals grow and become more numerous as they are carried by the wind, forming the characteristic wispy strands of cirrus clouds.

Because cirrus clouds are composed of ice crystals, they can sometimes indicate the presence of high-altitude turbulence or severe weather, such as thunderstorms or high winds. However, in general, cirrus clouds are considered harmless and are often associated with fair weather conditions.

Cirrus clouds are an important part of the Earth's climate system, as they play a role in regulating the planet's energy balance by reflecting sunlight back into space. They are also a popular subject for photographers and artists due to their unique appearance and the way they interact with the changing colors of the sky during sunrise and sunset.