@wee-pics Walter, the sun is BIG! About 1,000,000 miles in diameter at the solar equator. The parallel lines are sunlight between shadows cast by the clouds. From the Earth's perspective, all sunlight can thus be thought of as parallel, even though it isn't at all
Anyway, many kinds of clouds are a bit of a mystery. The cause of high level stratus clouds (50,000 to 80,000 feet) was only discovered about 15-18 months ago.
They are caused by the interaction between the solar wind (solar radiation) and interstellar radiation effecting the upper atmosphere at times when our Sun is quiescent or during Solar Minima.