Originally inspired by mirages and other types of natural phenomena like the twinkling of stars at night where the density of gas (as well as liquid), scientists in the 1860s devised an optical technique called Schlieren photography (the German word for ‘streak’) to isolate distorted light rays from factors such as heat, chemical reaction, and force.  Here is a hi-speed photo of a woman shooting a rifle in a Schlieren optical setup (a diagram for the setup can be found farther down the post)

Pretty friggun rad eh?!  Some of the most well known examples of Schlieren photography (and  related Shadowgraphs) are burning flames, and the billowing plumes of hot air that are only visible through this optical trickery.  Here is an example of a Bunsen Burner being lit by a blow torch with a colored gel/filter:

Yet another shot of the ordinarily invisible forces that come from the firing of a bullet:

Here is what a set-up for Schlieren has historically looked like, although there are a variety of methods to achieve a similar effect.

A Stanford Physics slow-motion video of a matchstick being struck (and subsequently blown out), used the incredibly unique and fluid forms of hot gases to win an award last year, see it below!

And here is a video from the Science Channel’s programming that explains the science behind it a bit better:

And some more ‘streaky’ candy from an NPR special on the subject of Schlieren:

More information on the science / physics behind it can be found here. 

Let’s send you off with a few more intriguing images:

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beware, and thanks for lookn! :}