eli5: cloudy weather but two shadows?


In some cloudy weather the car in front of me casts shadows to both left and right, but not back and front. The shadows are independent of the direction of the road but always perpeddicular to the road side. What is happening?

In: 1

For one, there are shadows off the back and front, they are just smaller and less noticeable.

It has to do with how light scatters through the clouds. On a clear day the light travels (relatively) straight down to the ground, hitting you uniformly, and casting a nice neat shadow on the ground.

But on cloudy day, those clouds scatter the light, making individual photons bounce around and change direction.

This means when you are standing there, some of the light hitting the left side of your face might have bounced off a cloud a mile to your left to come hit your left side, while the light hitting the right side of your face may have bounced off a cloud a mile to your right to come get your right side.

If you stack that up, you’ll find that the long side of the car is going block more of those erratic bounced photons than the short sides will, blocking relatively more light, creating a darker shadow.