eli5: How are we accurately able to study far off cosmic objects if our primary source of information is from light (that sometimes has traveled to us for 1000’s of years). Am I missing something?
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Light carries a lot of information!
I mean if you have fiber optic Internet, then light is carrying the information of the entire Internet to you!
Light even carries the signature of what a star is made of, if you breakdown the spectrum of light emitted by a distant star.
It’s just the way light works.
Why does light work that way? Nobody can really explain why light/photons exist in our universe: they just do, and again, they carry a sh * t ton of valuable info!
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EX:
If you shine a giant spotlight through a stained glass window, and another giant spotlight through a clear glass pane…
You’ll then be able to tell which one is shining through the stained glass window from countless miles and miles away.
In that way, the series of light waves/photons that reach your eyes, taken all together carry an imprint from the source from which they came from.
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Also if a distant object is larger than a star… Much larger than a star…
Say the size of a nebula or galaxy (light years across), then you can begin to get very detailed and intricate images of that cosmic object.
I mean, you’ve probably seen NASA photos of distant galaxies and nebulas right?
So that right there answers your question really well: just by looking at the photo of such a vast object, you can tell a lot about the object and its structure, shape, and even see how it’s an outward explosion, or whatever…
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NOTE: with our current telescope technology and resolving power, the distant object has to be INSANELY huge/vast to get that kind of detailed picture from so far away.
Again the object has to be multiple light years in size.
An object that large is so vast, that the human brain can’t really truly fully fathom or contemplate such a largeness.
Suffice to say, such cosmic objects are HUGE!
They would take our fastest space probes millions of years to cross–that’s how big they are.
So ya: if you’re looking at an object that big, then you’re going to see some stuff!
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As for the part of your question about light travelling for 1000’s of years…
Well, with these types of vast objects, it’s more like the light beam has travelled hundreds of thousands of years, to millions of years, to even upwards of 13 billion years!
So ya: the photon of light just travels through the vastness of space and keeps going and going until it hits something: like your telescope lens and photo sensor, or your eyeball.
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