When Spitzer launched Monday, 25 August 2003 at 1:35:39 a.m. EDT from Cape Canaveral Air Force Station in Florida, members of the Spitzer team were poised two miles away with an infrared camera. At that distance, the Delta II Heavy rocket carrying Spitzer was barely a speck, but in the infrared, the heat in the rocket's plume is extremely bright.
This clip shows the launch of Spitzer in the infrared, including the cooling of the plume after the rocket flies out of frame. The reason it looks like the clouds light up and come down to meet the rocket is because the clouds are reflecting (scattering) the bright infrared light of the hot rocket engines below.
Video Credit: NASA/JPL-Caltech
Spitzer in Space
Artist Concept - Spitzer Cover Ejection