Noctilucent clouds illuminate the night sky this summer
- Noctilucent clouds are formed in the mesosphere, at altitudes of 47-53 miles above Earth.
- These clouds are most often visible after sunset from late May to August in the northern hemisphere.
- The occurrence of noctilucent clouds highlights the complexity of Earth's atmosphere and its interaction with meteoric dust.
In the northern hemisphere, noctilucent clouds, Earth's highest clouds, begin to appear during late spring and summer months. These clouds, formed at altitudes of 47 to 53 miles (76 to 85 kilometers) in the mesosphere, are often visible after sunset under the right conditions. The prime viewing period lasts from late May to August, especially on clear nights, making it a remarkable celestial event for observers. What sets these clouds apart is their beautiful bluish glow at twilight, which can be seen with the naked eye without any special equipment. Noctilucent clouds are the result of a unique combination of conditions. They form in the coldest region of Earth’s atmosphere where water vapor interacts with meteoric dust from shooting stars. The dust—composed of sodium and iron atoms—settles on tiny ice crystals created in the extreme cold of the mesosphere, which can drop to temperatures as low as -120°C (-184°F). This process not only accounts for their formation but also contributes to their distinct shimmering appearance in the night sky. Researchers have noted that these clouds can reflect sunlight for extended periods, allowing them to be seen after sunset. When viewed, what observers perceive are the ripples reflecting within the icy formations. This optical phenomenon has attracted interest from scientists and skywatchers alike, especially since the arrival of NASA's Aeronomy of Ice in the Mesosphere (AIM) mission in 2007, focusing on how these formations relate to climate change and solar cycles. The mission aims to gain insight into whether changes in the mesosphere indicate broader climatic shifts on Earth. The best chances to observe these clouds occur far from the equator. In regions farther north, such as parts of Europe and Canada, the likelihood of witnessing this ethereal spectacle increases. As more people become interested in astronomy and the natural phenomena visible from Earth, noctilucent clouds serve as a stunning reminder of our planet's dynamic atmosphere and the subtle balances that govern it. This phenomenon invites awe and curiosity, encouraging both scientific inquiry and public interest in atmospheric science.