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Originally Posted by skyline5k
I have no problem seeing a supernova tonight and saying that it happened tonight. Just wanted to make sure I was understanding the distances involved.
Cas A exploded in 1680 for the record, but actually occurred about 10,000 years ago. That's what I was looking for. Cheers!
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You are understanding the distances involved correctly.
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On that note, the Sloan Great Wall (link), is around one billion light years from Earth. Therefore, many of the objects making up the wall may or may not even be there today.
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That's where it gets weird and almost philosophic. And it has to do with what your mean by "today" (and I'm not being a smart mouth
). Unless and until there is some sort of faster-than-light travel, we can really only interpret today, at least with regard to a specific star or object, as what we see today.
But on the other hand, when we talk about generalized things, such as what was the structure of galaxies in the very early Universe, looking at objects 10 billion light years away (and thus 10 billion years ago) is sort of looking at the past.
At least that's my take on it.