Wednesday, June 26, 2013

Night Dwellers

Never assume that what you can’t see isn’t there. Human beings by nature can only witness a fraction of what is out there, limited by our own biology and chemistry. Even the nearest stars (excluding our Sun) seem to disappear after sunrise but that doesn’t question their existence in whole now does it? At dusk, the stars reemerge, as they have done so for hundreds, thousands, millions, even billions of years, claiming their presence in the cosmos. And just as the stars have deemed themselves as night dwellers, at least from a human’s perspective, other bodies above us have also made reputations of shining at night; in this case, polar mesospheric clouds.

These clouds, also referred to as Noctilucent Clouds, exist approximately 80-85 km (≈50-53 miles) above the Earth’s surface near the coldest part of the atmosphere, the mesosphere. They become visible when tiny water particles (about 1/10,000 mm in diameter) in the upper atmosphere freeze into ice and reflect the sunlight. Polar Mesospheric clouds oftentimes appear in bluish hues because the stratospheric ozone layer absorbs most of the red light.

The formula for the development of these clouds in simple: low temperatures, water vapor, and a surface/nuclei for the water crystal to grow on. Once these criteria have been met, science takes over and with enough frozen water vapor and light the noctilucent clouds come to life. Next time you step outside and bear witness to these magnificent blankets that hover the horizon, thank the sun and the conditions of Earth’s upper atmosphere. Without either, the presence and existence of polar mesospheric clouds would be in question.

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