Light rays refract when passing through pockets of transparent fluids with different indices of refraction such as ordinary air pockets of varying temperature. This phenomenon makes night stars twinkle, distorts views above hot asphalt roads and hot barbeque grills, and provides an opportunity for visualizing the normally invisible movement of transparent gases and liquids. Schlieren and shadowgraph imaging allows for visualizing transparent gas density variations, allowing ordinarily unseen phenomena to be imaged and experimented with in real time. Traditional Schlieren systems require expensive equipment (DSLR camera, telephoto lens, several high-quality mirrors, an adjustable knife edge) and are difficult to align, while shadowgraph systems trade simplicity for image sensitivity. We outline a simplified classroom shadowgraph system that uses only a single telescope mirror, an LED flashlight, and an iPad to teach topics in high school science.

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Seeing the Invisible: Schlieren Imaging in SLOW MOTION
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What Does Sound Look Like? | SKUNK BEAR
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The light must be a single white LED as multiple LEDs will cause “shadowing” and “ghosting” effects.
6.
We successfully tested an iPad Air, iPad Mini (2nd Generation) iPad Pro 10.5 in, iPhone SE, iPhone 7, LG V10, Samsung Galaxy S6, Microsoft Surface 3, and Ipevo Ziggi-HD Document Camera.
7.
The concentric circle in the center of the mirror is due to the manufacturing process, but provides a valuable reference during setup. Given the choice, opt for a mirror with this “defect.”
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