ELi5: How does the whole light year thing work? How does something happen a long time ago that we know of yet we can still see it and have to wait for it to happen again (like those exploding star things on tt)
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Light is very fast, literally the fastest thing in the universe. It seems instant to us tiny humans but space is so big that light actually takes a long time to get around. So a light year is just the distance that light travels in a year. That’s why when you look at the stars in the sky you’re not actually seeing them in “real time” per se. You’re actually seeing how they were hundreds, thousands, or even millions of years ago because of how long the light from the star takes to reach Earth. In fact, you can actually tell how delayed what you’re seeing is if you know how many light years away something is. For example, if you’re looking at a star 1000 light years away, that means you’re actually seeing it as it was 1000 years ago, because the light took 1000 years to go the distance from the star to Earth.
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