SIRTF's Delta II in visible and infrared light

This side-by-side comparison image shows SIRTF's Delta II rocket in the 
late afternoon before launch. On the left is a photograph in visible light, 
while on the right is a false color infrared image showing the launch 
vehicle in the way SIRTF would see it.

The coldest surfaces in the infrared image are blue/black while the hottest 
ones are yellow/white. The comparison between these two images reveals many 
interesting features of infrared light.

In many places the infrared image almost mimics a photographic negative, 
with light objects in the visible photograph looking dark in the infrared 
and vice versa. This is not a simple photographic effect, but a result of 
the fact that darker surfaces absorb sunlight more efficiently and become 
hotter than lighter surfaces. 

This thermal evidence of light absorption is very obvious on the Delta 
rocket, where the white surfaces are cooler than the darker ones. Upon 
close examination, this is even obvious on the lettering and designs on the 
various labels on the rocket and adjacent tower. In all of these places the 
heat patterns in the infrared image highlight the darker colors.

The very hottest surfaces in the picture are seen near the lower left side: 
the dark interior of a hatchback car, a dark camera on a tripod, and even 
the dark blue portion of an American flag in the distance.

The infrared image also reveals a variety of features that can not be seen 
at all in the visible photograph. The rocket payload faring containing 
SIRTF is kept air conditioned, and several cool bands associated with this 
cooling can be seen on the upper white portion of the rocket. Also, the 
division between the lower empty fuel tanks and second stage rocket can be 
seen just below this as a cooler segment of the blue tube. 

Even the gantry in the foreground at the upper left shows warmer bands on 
the metal surface where braces run on the back side; in the visible photo 
there is no sign of these hidden structures.