>>What would the shadow and light of the contrail from a plane look like when it flies parallel to the ground, vs. what would the shadow and light of the contrail from a missile look like when it flies perpendicular to the ground?<<
That is one of the things that convinced me this is a contrail. You notice in the op snapshot that there is a dark streak just “above” the contrail that goes all the way to the right alongside the contrail. This is what happens when the clouds (and in this case, clouds and haze) at one level is below the contrail. Because both are parallel to the earth, you get a shadow that looks like the contrail’s reverse image mate. In this case, the clouds are not all that much lower than the contrail, so the shadow is close. I’ve seen situations where the shadow was in a layer of clouds far lower than the contrail and there is a significant gap, but the contrail and shadow are always parallel, as in this case.
If it were a missile launch, it COULD be parallel, depending on the angle of the sun in relation to your viewing angle, but generally speaking the shadow is usually not parallel and can range from parallel to perpendicular to the plume. It also adjusts in shape based on altitude.
I’m making it too complicated. Sorry...
-PJ