Plume of engine combustion products

The plume of engine combustion products is visible only when it turns out to be "sufficiently dense"according to the beam of vision. If such a plume gets between the sun and the observer, it may look like a dark cloud. But the rocket has absolutely round engine nozzles, and the technogenic cloud turns out to be exceptionally correct in shape.

Moreover, if an observer (for example, on an airplane) moves along or across an "invisible" rocket plume, he will see amazing pictures — the sudden appearance of a dark or (depending on the position of the Sun) a fireball, the transformation of the ball into an ellipse-dish, and even "disappearance without a trace".