A Schlieren image of a balloon popping. To increase the schlieren effect, the balloon is filed with pure carbon dioxide gas. The carbon dioxide gas has a different index of refraction than air, so the mixing can be clearly seen when the balloon is popped. The schlieren image identifies areas of different temperature by using the change in the index of refraction of a fluid due to a change in temperature. This image was captured using a high speed flash with a duration of 1/1,000,000th of a second.