At low altitudes, fluffy cotton-like cumulous and dark-gray nimbostratus clouds garnish the sky, changing daily. Higher in the atmosphere, clouds become thinner and wispier, like cirrus clouds.

Some clouds may be slightly darker than background sky and others may be slightly brighter, but it is those differences that reveal their presence as obscuring dark nebulae. This small, wispy dark ...

He added that the cloud "grows so tall, but stays so narrow, that it blocks light from the setting sun and casts a shadow across the sky." Cappucci also said the dark band seen in the clip is ...