NLC: Noctilucent Clouds

NLC (Noctilucent Clouds): Mysterious Nighttime Clouds

Noctilucent clouds (NLCs), also known as night-shining clouds, are the highest clouds in Earth’s atmosphere, forming at altitudes of about 76-85 km (47-53 miles) in the mesosphere. These rare atmospheric phenomena occur when water vapor condenses onto tiny particles of cosmic or volcanic dust at high altitudes. NLCs primarily appear in polar regions, although they can occasionally be seen at lower latitudes.

Period of Occurrence

NLCs are most commonly observed during the summer months, from June to August in the Northern Hemisphere and from November to February in the Southern Hemisphere. The best time to see them is at night, just after sunset or before sunrise, when the Sun is below the horizon but still illuminates these high-altitude clouds.

Scientific Facts

• Altitude: NLCs form at an altitude of approximately 80 kilometers (50 miles), making them the highest clouds on Earth.
• Temperature: These clouds form in extremely cold conditions, with temperatures in the mesosphere dropping to around -120°C (-184°F).
• Composition: NLCs are composed of tiny ice crystals that condense on dust particles, creating their characteristic silvery-blue appearance.

Curiosities

• Polar Mesospheric Clouds: NLCs are also known as polar mesospheric clouds (PMCs) because of their formation in the polar regions of the mesosphere.
• Recent Discovery: NLCs were first observed in 1885, shortly after the eruption of Krakatoa, leading some scientists to speculate that volcanic ash may have contributed to their formation.
• Brightness: The brightness and frequency of NLCs have increased over the past few decades, possibly due to climate change and the increasing presence of methane in the atmosphere, which leads to more water vapor in the upper atmosphere.

Viewing Tips

To observe NLCs, look towards the twilight sky in the direction of the Sun’s recent setting or upcoming rise. These clouds are most visible from higher latitudes, though they can sometimes be seen as far south as 40° latitude. Binoculars can enhance the viewing experience, but NLCs are generally visible to the naked eye.