What does UV mean?

Answer 1

"UV" stands for "ultra-violet". We measure light in colors; red light has the least energy, and violet has the most. Light that has even less energy than red light is called "infra-red" or IR; this means "below red". Light that has even more energy than violet is called "ultra-violet", or UV; this means "above violet".

The electromagnetic spectrum covers everything from radio to microwaves to heat to light to X-rays to gamma rays, as you go up the spectrum increasing in frequency and energy. UV and IR are the bands just above and just below the "visible light" spectrum.

Electromagnetic radiation of ALL frequencies is emitted by the Sun, but each star has its own peak of color and radiation. We evolved here on Earth, in an atmosphere that selectively absorbs and blocks some frequency ranges. The most transparent is the band that we call "visible light"; our eyes evolved to see these frequencies BECAUSE they were the most useful ones for life HERE, on the Earth. If we ever meet aliens in space, the chances are that they will "see" in different bands, because THEIR atmosphere will be different than ours; if they even HAVE an atmosphere like Earth does.