Why does the cloud in a straight line as if someone draw a line in the sky with a straight edge?

Question

My cousin took one of the pictures below (the middle) in the evening in BKK and she confirmed that she took it with her phone. I’ve been trying to explain it. I thought it had to do with hot air and the buildings. At first I thought where there was no cloud the air was hotter (which dispersed the cloud away). All those buildings used AC so they absorbed the heat from the sun all day, but on the street between the building not much heat(from the sun) was absorbed so this heat was reflected up into the air and dispersed the cloud. But looking at the wider picture, this explanation still makes no sense. It’s something in the sky!!! Can anyone come up with a good explanation?

electromagnetic radiation thermodynamics visible light

Bob Jacobsen · Answer

The Sun is so low to the horizon that it’s illuminating the high, wispy clouds from underneath. Where it’s dark, something (probably a cumulus cloud) is blocking that light.

The thin cloud in the resulting shadow is still there if you look closer, but it’s much harder to see because it’s not illuminated.

The line is so straight because Sun's light is just barely grazing the bottom of the wispy clouds.  That line is the geometric projection of only the bit of the cloud that's throwing the shadow at just the right altitude.

Why does the cloud in a straight line as if someone draw a line in the sky with a straight edge?

One Answer

Add your own answers!

Ask a Question