🌈 Light and colour

A mirror has a very smooth, shiny surface that bounces light back in a neat, organised way instead of scattering it, which is exactly why you can see a clear reflection of yourself in it. Light from you hits the mirror and bounces straight back to your eyes at a matching angle, so your reflection lines up perfectly with the real you. A rough or bumpy surface would scatter that same light in every direction, which is why only smooth surfaces make good mirrors.

Our eyes have tiny colour-sensing parts inside them, and everyone's eyes are built just a little bit differently, so the exact same colour can look slightly different from one person to the next. Lighting also changes how a colour appears, the same shirt can look bright blue in sunlight and almost grey in dim light. A small number of people cannot easily tell red and green apart, this is called colour blindness, and it happens when those colour-sensing parts work a bit differently.

Light travels in straight lines, incredibly fast, until it hits something that blocks, bends or bounces it. That is exactly why shadows have sharp, straight edges instead of curving around objects, the light simply cannot bend around a shape blocking its path. Light travels so fast that it could circle the entire Earth about seven times in just one second, which is why a light switch seems to light up a room instantly.

Some special materials can soak up light energy while the lights are on, then slowly release that stored energy back out as a soft glow once it goes dark. Glow-in-the-dark stars and stickers need to actually be "charged" under a bright light first before they will glow later, and the glow always fades as the stored energy runs out. That is different from something like a firefly, which makes its own glow using a chemical reaction inside its body, without needing to be charged by any outside light at all.