Okay, I need some discussion. I love love love reading about the universe and such. All the stars and planets out there, it’s amazing to me! But I’ve never been able to understand light years. Like, we could be looking at something in the sky and be all “Ooooh that’s a bright star!” But it’s 100 light years away and for all we know the star is actually dead and we are seeing the light as it had been traveling to us but died previously. This just goes right over my head. How do we just determine all these objects in the sky are so far… how do we know how far the light from thst object has been traveling? Please help lol! How do we also see planets so far away… I know we have amazing technology but damn… that’s insane to be able to see objects just so far away! I also think there must be some form of life out there. There’s no way we are the only planet with something living on it! Thanks for your input!
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> How do we just determine all these objects in the sky are so far… how do we know how far the light from thst object has been traveling?
Generally distances to any object in space are determined using the [distance ladder](https://en.wikipedia.org/wiki/Cosmic_distance_ladder), so named because using each “rung” of the ladder requires that you first get to the one before it. For nearby stars (100 ly is considered nearby), we only need the first “rung” of the ladder, known as parallax. As the Earth orbits the sun throughout the year, stars that are close to us will appear to drift slightly compared to the background of, say, galaxies that are *millions* of lightyears away. To understand what this is, try holding your thumb up with your arm extended with a wall behind it. Close your left eye, and then close your right eye, and watch as your thumb “moves” across the wall behind it. If you know the distance between your eyes and the angle that your thumb moves, you can calculate the length of your arm. Astronomers can see the same movement in nearby stars, and can do the same calculation to determine distance.
> How do we also see planets so far away…
Usually astronomers *don’t* see planets themselves. Most exoplanets are discovered when they pass in front of their star, and the star dims slightly. Rarely, though, if some exo-solar system is oriented so that we’re looking “down” on it, astronomers can block the light from the star and very faint light from planets orbiting the star. The [Wikipedia page](https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets) has a pretty good graphic of this; there’s a very dark region in the middle, and surrounding that there’s some light moving around. With powerful enough telescopes, astronomers are able to detect that light
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