We showed people what they looked like in ultraviolet, & wondered aloud if they wanted to put on some damn sunscreen already.
Music: ‘Summer in the City – Starcadian remix’ by Freedom Fry.
Astronomer Phil Plait explains:
The genius part here was giving people sunscreen. The camera detects UV from the Sun that’s reflected off people’s skin; the point of sunscreen is to absorb that UV so it doesn’t even reach the skin. Since no UV is reflected from sunscreen, it appears black in the video, even though in visible light it looks white. It looks like people are smearing crude oil on their faces, which is pretty funny.
I contacted Leveritt, and he informed me that he used an AstroDon UVenus filter and a camera with a CMOS detector. Looking that information over, I think he was detecting light around a wavelength of 330–380 nanometers, smack dab in the UVA range.
It’s fascinating to see how skin looks different there. Melanin, a pigment in the skin, absorbs ultraviolet light much more than visible, so in the video patches of melanin—freckles!—look very dark. Glass blocks UV light quite well, especially in modern eyeglasses which are coated with a layer specifically designed to protect our eyes from solar UV. In the video it’s obvious that works.
Interestingly, some people’s teeth are very reflective in UV, and others’ weren’t. Plaque, resins in fillings or crowns, food, and enamel all absorb different amounts and colors of UV, probably accounting for those differences, too.