Noctilucent clouds are rare, high-altitude clouds that form in the upper atmosphere, typically around 80 kilometers (50 miles) above the Earth's surface. They are composed of ice crystals and are most visible during twilight when the sun is below the horizon, illuminating them from below. These clouds appear as glowing, bluish-white wisps and are often seen in polar regions during summer months. These clouds are thought to be linked to climate change and may indicate changes in atmospheric conditions. Their formation requires specific conditions, including low temperatures and the presence of water vapor, making them a fascinating subject for scientists studying the Earth's atmosphere.