Tis the Season for Night Shining Clouds
A bright display of noctilucent clouds last night prompts me to remind northerners to look north at this prime season for night shining clouds.
Noctilucent clouds (NLCs) can be seen only in summer and are best in the few weeks before and after (mostly after) summer solstice. I shot all these images in the middle of the night. Indeed, the two images above and just below are from 3 am on the morning of June 27.
NLCs are high altitude clouds at the edge of space some 80 kilometres above the Earth, far above any normal weather clouds. Their height allows sunlight streaming over the pole to illuminate them all night long.
Their cause is a mystery. They may form by water vapour condensing on meteoric dust particles.
They look luminescent, as if glowing on their own. But these are not auroras. They shine only by reflected sunlight.
And they have complex structures, with intricate waves and ripples.
And they move very slowly, as this time-lapse from June 17 shows.
Readers living at a latitude between 45° and 55° are best situated to see “NLCs.” From farther south the clouds will be below the horizon. From farther north the sky may be too bright with twilight and the angle of illumination wrong for optimum viewing.
For more information, check the Wikipedia article.
Unlike auroras, there is no predicting when they might appear. Some nights when it is clear where you are, no NLCs appear. Perhaps that’s because of cloud much farther north blocking the path of light from the Sun on the other side of the planet to the clouds on our side of the Earth.
But by the end of July NLC season is coming to an end as the Sun drops farther below the northern horizon at night, and the nights get darker.
So over the next four weeks, look low in the north for night shining clouds.
— Alan, June 27, 2016 / © 2016 Alan Dyer / www.amazingsky.com