Huygens’ principle is not an easy physical concept to grasp and I've often tried to avoid it (if possible). But at last making this animation made it a little clearer (to me).[br]You can control:[br]v1 and v2 (light speeds in the media 1 and 2)[br][math]\delta[/math]=distance between adjacent light rays[br]nr: number of rays[br][math]\alpha[/math]:angle of incidence (with respect to the horizontal line)[br]You'll probably need to adjust the font size and layout to match your screen resolution.[br]Gif in twitter:[br][br][url=https://twitter.com/sfera314/status/1495725283751649280?s=20&t=TB13K_u9BlM_upvy0uvSPQ]https://twitter.com/sfera314/status/1495725283751649280?s=20&t=TB13K_u9BlM_upvy0uvSPQ[br][br][/url]