The first indication of a successful liftoff is an extremely bright light from the ignition of the Solid Rocket Motors. (The Space Shuttle Main Engines burn pure hydrogen and are not as visible.) Because sound travels much more slowly than light, the noise generated by the launch—which we didn't hear at all due to the prevailing winds—takes much longer to arrive. There is also a noise suppression system, in which 300,000 gallons of water are dumped on the launch pad; the absorption of energy by the water turning into steam reduces that available to make noise and vibrations that damage launch pad facilities. In this photo you can clearly see the orange-colored external tank between the two SRBs; the Shuttle orbiter itself is on the other side.
Copyright 2011, Garrett Wollman. All rights reserved. Photograph taken 2011-02-24.