Hello again. Haven't been here for a while. Tom Bishop's explanation serves, however a much more accurate one:
Parts of the atmosphere, due to their relative pressures, temperatures and densities, act as mirrors. These high-pressure atmospheric reflecting pockets usually hang around at low altitude, usually so close to the ground you do not notice them. The reason the top of the smoke column is illuminated is simply because the conspiracy equip the shuttle's solid rocket boosters with slow-burning magnesium as well as other materials to simulate the effect, thus maintaining the illusion of a round Earth.
The main reason for the conspiracy is that there is a centuries-old bet between the nations, basically Europe bet America and Russia they couldn't convince the world was spherical without the truth leaking out. (This bet is between secret governments, obviously) and America and Russia don't want to end it, because they would have to pay Europe so much money they would be bankrupt. Recently, China took up the bet too.