This is a photo of an F-14 Tomcat just as it was breaking the sound barrier on a humid day. What you are seeing is the water vapor in the air being compressed into a cloud around the aircraft by the shockwave created as the aircraft passed through the sound barrier.
Click on the photo if you want to download a short video clip of an F-14 Tomcat breaking the sound barrier. The file size is fairly large so expect it to take a few minutes to download if you're using a dial up modem. Your Windows Media player should launch automatically and then you can save it to a file after it's completed downloading if you want to save it. You can download the latest Windows Media player from the Microsoft Update page at no charge.
The F-117 Nighthawk Stealth Fighter
The A-10 Thunderbolt (Warthog)
The F-22 Raptor
The Lockhead Experimental Tactical Fighter
The F-15 Eagle
The F-16 Fighting Falcon
Another sound barrier being broken. This time by an F-18
The B-1 Bomber (Lancer)
The B-2 Stealth Bomber (Spirit)