Noctilucent clouds are rare, high-altitude clouds that form in the mesosphere, about 50 to 85 kilometers above the Earth's surface. They are composed of ice crystals and are typically visible during twilight when the sun is below the horizon, illuminating them from below. These clouds appear as glowing, bluish-white wisps in the sky. These clouds are most commonly observed in polar regions during summer months, but they can occasionally be seen at lower latitudes. Noctilucent clouds are thought to be influenced by climate change, as they may form more frequently due to increased water vapor in the upper atmosphere.